Numerical study of molten and semi-molten ceramic impingement by using coupled Eulerian and Lagrangian method

Large temperature gradients are present within ceramic powder particles during plasma spray deposition due to their low thermal conductivity. The particles often impinge at the substrate in a semi-molten form which in turn substantially affects the final characteristics of the coating being formed. This study is dedicated to a novel modeling approach of a coupled Eulerian and Lagrangian (CEL) method for both fully molten and semi-molten droplet impingement processes. The simulation provides an insight to the deformation mechanism of the solid core YSZ and illustrates the freezing-induced break-up and spreading at the splat periphery. A 30 μm fully molten YSZ particle and an 80 μm semi-molten YSZ particle with different core sizes and initial velocity ranging from 100 to 240 m/s were examined. The flattened degree for both cases were obtained and compared with experimental and analytical data

Spectral signatures of thermal spin disorder and excess Mn in half-metallic NiMnSb

Effects of thermal spin disorder and excess Mn on the electronic spectrum of half-metallic NiMnSb are studied using first-principles calculations. Temperature-dependent spin disorder, introduced within the vector disordered local moment model, causes the valence band at the $\Gamma$ point to broaden and shift upwards, crossing the Fermi level and thereby closing the half-metallic gap above room temperature. The spectroscopic signatures of excess Mn on the Ni, Sb, and empty sites (Mn$_\mathrm{Ni}$, Mn$_\mathrm{Sb}$, and Mn$_\mathrm{E}$) are analyzed. Mn$_\mathrm{Ni}$ is spectroscopically invisible. The relatively weak coupling of Mn$_\mathrm{Sb}$ and Mn$_\mathrm{E}$ spins to the host strongly deviates from the Heisenberg model, and the spin of Mn$_\mathrm{E}$ is canted in the ground state. While the half-metallic gap is preserved in the collinear ground state of Mn$_\mathrm{Sb}$, thermal spin disorder of the weakly coupled Mn$_\mathrm{Sb}$ spins destroys it at low temperatures. This property of Mn$_\mathrm{Sb}$ may be the source of the observed low-temperature transport anomalies.Comment: 5 pages, 7 figures, updated version with minor revisions and an additional figure, accepted in Phys. Rev. B (Rapid Communication

A numerical model for the fractional condensation of pyrolysis vapours

Experimentation on the fast pyrolysis process has been primarily focused on the pyrolysis reactor itself, with less emphasis given to the liquid collection system (LCS). More importantly, the physics behind the vapour condensation process in LCSs has not been thoroughly researched mainly due to the complexity of the phenomena involved. The present work focusses on providing detailed information of the condensation process within the LCS, which consists of a water cooled indirect contact condenser. In an effort to understand the mass transfer phenomena within the LCS, a numerical simulation was performed using the Eulerian approach. A multiphase multi-component model, with the condensable vapours and non-condensable gases as the gaseous phase and the condensed bio-oil as the liquid phase, has been created. Species transport modelling has been used to capture the detailed physical phenomena of 11 major compounds present in the pyrolysis vapours. The development of the condensation model relies on the saturation pressures of the individual compounds based on the corresponding states correlations and assuming that the pyrolysis vapours form an ideal mixture. After the numerical analysis, results showed that different species condense at different times and at different rates. In this simulation, acidic components like acetic acid and formic acids were not condensed as it was also evident in experimental works, were the pH value of the condensed oil is higher than subsequent stages. In the future, the current computational model can provide significant aid in the design and optimization of different types of LCSs

Starved State Dependent Modulation of Olfactory Receptor Neuron Function in Drosophila melanogaster larvae

The ability of olfactory neurons to locate food sources underlies survival in most species of the animal kingdom. This ability of olfactory neurons to process environmental information is often modulated by the animal’s internal state such as hunger. The peripheral end of the olfactory circuit consists of first order olfactory receptor neurons (ORNs), that synapse onto the second order projection neurons (PNs), and regulatory local neurons (LNs) that innervate ORNs and PNs. While a considerable amount of information has been generated, in various animal systems, regarding sensory neuron responses to food odorants and modulation of these responses by hunger, much less is known about the extent of modulation that exists among individual sensory neurons and its impact on driving behavioral output. We hypothesized that starvation differentially alters the sensitivity of individual first-order Olfactory Receptor Neurons (ORNs). To test this hypothesis, we exposed starved or non-starved third instar Drosophila larvae to specific odorants to analyze the effect of individual ORN activity on chemotaxis. We used two different behavioral paradigms to analyze the chemotaxis response of larvae to odorants. When tested with odorants that elicit strong physiological responses from individual ORNs, starved and non-starved larvae showed different behavioral responses in these behavioral paradigms. However, the extent of behavioral differences among starved and non-starved larvae varied when different odorants were tested in the assays. Further, we provide evidence that this modulation of ORN function by starvation is mediated by GABA signaling pathway. To investigate the molecular basis for this differential modulation, we used immunohistochemistry and gene expression analysis. We developed an antibody against the GABA (B) receptor to look at the localization of GABA receptors in the olfactory neurons. We found that GABA (B) receptors are localized at the ORN synapses. We used qRT-PCR analysis to identify other molecular players that are involved in starvation control. We conclude that an animal’s internal state such as hunger differentially modulates the functions of individual ORNs to impact olfactory information processing. Our results support recent studies from our lab and other groups that suggest that ORNs are functionally diverse. Overall, this research thesis has implications for understanding peripheral odor coding

Analysis of random packing of uniform spheres using the Monte Carlo simulation method

The study of random packing of spheres has had a long history. It particularly interests many researchers because randomly packed hard spheres exhibit some features of the properties of simple liquid, e.g. the packing density and the radial distribution. Many researchers have studied random packing both experimentally and also by using computer simulation. Monte Carlo simulation method was used to generate random loose packing of hard spheres. Packing characteristics like packing density, radial distribution function, co-ordination, angular distribution and fabric tensor have been computed for this packing system. The packing density for a system of 8000 particles with a diameter of 0. 15 was computed to be 0.582. The packing density obtained for random packing of loose spheres is in good agreement with Owe Berg [2], Tory [18] and about 2% less than the experimental values of Scott [9]. The radial distribution function for the 8000-particle system was also computed for the packing bed. The peak occurrence in the radial distribution plot was found to be in good agreement with Scott [9], Nolan [ 11 ] and Powell [ 17]. An average co-ordination number for the same size system was computed to be 6.71291 ±0.023433 which is in good agreement with Smith [12], Visscher [1], Nolan [11]. Angular Distribution of the particles was also found by computing the contact angles for all the spheres with their neighbors. The histogram of the contact angles shows that there is no preferred direction for the particles, which shows the packing is completely random and that there is no particular pattern in their arrangement. The fabric tensor was computed. The analysis of fabric tensor shows that all the planes in the packing assembly, generated by the Monte Carlo simulation, are principal planes. Similar situation exists in ideal fluid. Hence it is shown that the Monte Carlo simulated assembly can serve as model for ideal fluid