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Influence of glycerol on plasma electrolytic oxidation coatings evolution and on corrosion behaviour of coated AM50 magnesium alloy
No full textPEO coatings were obtained from base silicate electrolyte (bPEO) and glycerol added silicate electrolytes (gPEO) for different processing times. PEO coatings' evolution and their corrosion behavior were systematically studied as a function of PEO processing time. Smaller maximum pore size and higher pore density have been discerned for gPEO compared to bPEO for all the PEO processing time. Glycerol addition resulted in reduced coating thickness, promoted periclase, MgO, formation and suppressed forsterite, Mg2SiO4, amorphization. From electrochemical impedance spectroscopy study, it was found that gPEO had better corrosion resistance as compared to bPEO
Evaporative Crystallization of Spirals
No full textSpiral motifs are pervasive in nature, art, and technology due to their functional property of providing compact length. Nature is particularly adept at spiral patterning, and yet, the spirals observed in seashells, hurricanes, rams' horns, flower petals, etc. all evolve via disparate physical mechanisms. Here, we present a mechanism for the self-guided formation of spirals from evaporating saline drops via a coupling of crystallization and contact line dynamics. These patterns are in contrast to commonly observed patterns from evaporation of colloidal drops, which are discrete (rings, concentric rings) or continuous (clumps, uniform deposits) depending on the particle shape, contact line dynamics, and evaporation rate. Unlike the typical process of drop evaporation where the contact line moves radially inward, here, a thin film pinned by a ring of crystals ruptures radially outward. This motion is accompanied by a nonuniform pinning of the contact line due to crystallization, which generates a continuous propagation of pinning and depinning events to form a spiral. By comparing the relevant timescales of evaporation and diffusion, we show that a single dimensionless number can predict the occurrence of these patterns. These insights on self-guided crystallization of spirals could be used to create compact length templates
Real-Time Status Updates for Markov Source
No full textFor timely sensor update, the traditional approach is to send new information at every available opportunity. Recent research has shown that with limited receiver feedback, sensors can improve the update timeliness by transmitting differential information for slowly varying correlated sources. One can elect to transmit either the actual or the differential state information based on a differential encoding threshold for a general Markov source. This threshold captures the natural trade-off between differential transmission opportunities and the coding gains. Using matrix-geometric method, we find the limiting age distribution for a Markov source as a function of the encoding threshold, from which several other performance metrics of interest, such as mean age, peak age, and the probability of decoding failure can be derived
Correlated Electronic States of a Few Polycyclic Aromatic Hydrocarbons: A Computational Study
No full textIn recent years, polycyclic aromatic hydro-carbons (PAHs) have been studied for their electronic properties as they are viewed as nanodots of graphene. They have also been of interest as functional molecules for applications such as light-emitting diodes and solar cells. Since the last few years, varying structural and chemical properties corresponding to the size and geometry of these molecules have been studied both theoretically and experimentally. Here, we carry out a systematic study of the electronic states of several PAHs using the Pariser-Parr-Pople model, which incorporates long-range electron correlations. In all of the molecules studied by us, we find that the 2A state is below the 1B state and hence none of them will be fluorescent in the gaseous phase. The singlet-triplet gap is more than half of the singlet-singlet gap in all cases, and hence, none of these PAHs can be candidates for improved solar cell efficiencies in a singlet fission. We discuss in detail the properties of the electronic states, which include bond orders and spin densities (in triplets) of these systems
Large intrinsic magnetization in an epitaxial BiFeO3/NdGaO3 system
No full textWe report a comparative study of the crystal structure and magnetic properties between (001) oriented epitaxial BiFeO3 films grown on NdGaO3 and SrTiO3 substrates without any magnetic parasitic phase. The 15nm BiFeO3 film deposited on a NdCaO3 substrate shows substantially high magnetization (similar to 250 emu/cc) as compared to an identically thick BiFeO3 film (similar to 100 emu/cc) deposited on a SrTiO3 substrate. Detailed structural analysis revealed that the high magnetization is associated with a monoclinic (Cm) like distortion of the BiFeO3 crystal structure. We corroborated our experimental findings with first principles density functional theory calculations which suggested a saturation magnetization (266 emu/cc) close to the experimentally obtained one and a ferromagnetic ground state with the high spin moment in the Cm phase
Kolmogorov-Crespi Potential For Multilayer Transition-Metal Dichalcogenides: Capturing Structural Transformations in Moire Superlattices
No full textWe develop parameters for the interlayer Kolmogorov-Crespi (KC) potential to study structural features of four transition-metal dichalcogenides (TMDs): MoS2 WS2, MoSe2, and WSe2. We also propose a mixing rule to extend the parameters to their heterostructures. Moire super lattices of twisted bilayer TMDs have been recently shown to host shear solitons, topological point defects, and ultraflat bands close to the valence band edge. Performing structural relaxations at the density functional theory (DFT) level is a major bottleneck in the study of these systems. We show that the parametrized KC potential can be used to obtain atomic relaxations in good agreement with DFT relaxations. Furthermore, the moire superlattices relaxed using DFT and the proposed force field yield very similar electronic band structures
All optical dynamic nanomanipulation with active colloidal tweezers
No full textManipulation of colloidal objects with light is important in diverse fields. While performance of traditional optical tweezers is restricted by the diffraction-limit, recent approaches based on plasmonic tweezers allow higher trapping efficiency at lower optical powers but suffer from the disadvantage that plasmonic nanostructures are fixed in space, which limits the speed and versatility of the trapping process. As we show here, plasmonic nanodisks fabricated over dielectric microrods provide a promising approach toward optical nanomanipulation: these hybrid structures can be maneuvered by conventional optical tweezers and simultaneously generate strongly confined optical near-fields in their vicinity, functioning as near-field traps themselves for colloids as small as 40 nm. The colloidal tweezers can be used to transport nanoscale cargo even in ionic solutions at optical intensities lower than the damage threshold of living micro-organisms, and in addition, allow parallel and independently controlled manipulation of different types of colloids, including fluorescent nanodiamonds and magnetic nanoparticles
Facilitation of Nucleation of Polymorphic Solids due to the Presence of Multiple Metastable Phases: Effects of Nonclassical Surface Tension
No full textSurface tension plays an integral part in our discussions on the formation of new phases from melt, although a quantitative understanding of the surface tension is almost completely lacking, especially in the synthesis of polymorphic solids. This lacuna can be appreciated if we realize that even a semiquantitative understanding of the celebrated Ostwald's step rule does not exist. A dramatic lowering of the surface energy of a growing nucleus happens when the stable phase grows from melt in the presence of several amorphous metastable phases. The later phases have characteristics intermediate between the initial and final phases. This reduction in surface tension may dictate the rate of both nucleation and growth in a manner hitherto unexplored. In this work, an order parameter-based approach is developed and applied to quantify the effects of such metastable phases. Interestingly, the total surface energy between melt and stable solid phases displays a fractional dependence on the number of metastable phases (N-MS). At higher temperature, this effect is observed to be much stronger. This fractional dependence of surface energy is related to the curvature of free-energy surface (that varies with temperature, pressure, etc.), assumed plausible ordering of metastable phases in the interface, and has consequence in nanomaterial synthesis
Prediction of variation of oxides of nitrogen in plasma-based diesel exhaust treatment using artificial neural network
No full textDiesel exhaust treatment in plasma environment is a complex phenomenon mainly involving oxidation of several gaseous pollutants. With the help of artificial neural network, an attempt has been made in this paper to predict the variation of nitric oxide/nitrogen dioxide when the exhaust is subjected to discharge plasma. Electrical (power and frequency) and physical (engine load and flow rate) parameters have been considered as inputs of a three-layered artificial neural network model to track the performance of the treatment. Two different backpropagation algorithms named Bayesian regularization and Levenberg-Marquardt have been applied to compare the prediction performance. Bayesian regularization training algorithm shows better agreement with the experimental data than Levenberg-Marquardt in terms of root-mean-square error and correlation coefficient. Further, sensitivity analysis has been carried out to obtain an insight about the relative importance of input parameters on output parameters. This investigation shows that the applied input power is the most influential among the four input parameters from the point of variation of nitric oxide/nitrogen dioxide
Monsoon season local control on precipitation over warm tropical oceans
No full textUnderstanding local SST control on precipitation during monsoon is important for deducing climate change due to global warming, particularly for warm oceans. Studies of the relationship of the precipitation over tropical oceans with local sea surface temperature (SST), on the monthly scale, have shown that the propensity for precipitation is high for SST above a threshold of 27.5 C. However, for warm oceans with SST above the threshold such as the Bay of Bengal and South China Sea, for each SST, there is a large variation of precipitation and the SST-precipitation relationship is weak. On daily scale mean precipitation increases slightly with SST when precipitation lags SST by a few days, but the relationship between them is rather weak. But, when SST is above the threshold, for daily, pentad, 10-day and monthly time scales, and with or without time lag, the curve depicting the variation of mean precipitation with SST explains only a small fraction of precipitation variance and hence cannot be considered to be representative of the SST-precipitation relationship, or used to deduce the impact of SST on precipitation. On the other hand, the local control on precipitation is predominantly atmospheric dynamics with the relationship of variation of precipitation to low-level convergence on all timescales, being strong. This suggests that for warm oceans, the limiting resource for precipitation/convection is not SST but dynamics