Mass transfer around prolate spheroidal drops in an extensional flow

Mass transfer in the continuous phase around a small eccentricity prolate spheroidal drop in an axisymmetric extensional creeping flow and at large Peclet numbers was investigated theoretically. The results show that, at very short times, the total quantity of solute transferred to or from the drop represents, at O(Ca¹), mass transfer by diffusion only around a sphere. For long times, or at steady‐state, the total quantity of solute transferred is, at O(Ca¹), slightly smaller than that of a spherical drop, and it decreases with an increase of the capillary number or the viscosity ratio. © 2012 Canadian Society for Chemical Engineering     

Mathematical Modeling of Drying of Liquid/Solid Slurries in Steady State One-Dimensional Flow

ABSTRACT

A mathematical model of simultaneous mass, heat and momentum transfer for two-phase flow of a gas and a solid/liquid slurry was developed. The model was applied to calculation of the drying process of coal-water slurry droplets in a gas medium in a steady one-dimensional flow. The model was based on the well-known two-stage drying process for slurry droplets. After the first period of drying, in which the evaporation rate is controlled by the gas phase resistance, the evaporating liquid diffuses through the porous shell (crust) and then, by convection, into the gas medium. Inside the dry external crust of the drop, a wet central core forms, which shrinks as evaporation proceeds. The temperature of the slurry droplet rises. The process ends when the temperature of the dry outer crust reaches the coal ignition temperature in the case of combustion or when the moisture of the particle reaches the final required moisture. The developed model was based on one-dimensional balance equations of mass, energy and momentum for the liquid/solid and gas phases. The system of governing equations was represented by first-order differential equations and solved simultaneously. The numerical solution of the governing equations was obtained using Gear's method. The model permitted calculation     

Arabidopsis thaliana Plants with Different Levels of Aliphatic- and Indolyl-Glucosinolates Affect Host Selection and Performance of Bemisia tabaci

Generalist insects show reduced selectivity when subjected to similar, but not identical, host plant chemical signatures. Here, we produced transgenic Arabidopsis thaliana plants that over-express genes regulating the aliphatic- and indolyl- glucosinolates biosynthetic pathways with either a constitutive (CaMV 35S) or a phloem-specific promoter (AtSUC2). This allowed us to examine how exposure to high levels of aliphatic- or indolyl-glucosinolates in homogenous habitats (leaf cage apparatus containing two wild-type or two transgenic leaves) and heterogeneous habitats (leaf cage apparatus containing one wild-type and one transgenic leaf) affects host selection and performance of Bemsia tabaci, a generalist phloem-feeding insect. Data from homogenous habitats indicated that exposure to A. thaliana plants accumulating high levels of aliphatic- or indolyl-glucosinolates negatively affected the performance of both adult females and nymphs of B. tabaci. Data from heterogeneous habitats indicated that B. tabaci adult females selected for oviposition plants on which their offspring perform better (preference-performance relationship). However, the combinations of wild-type and transgenic plants in heterogeneous habitats increased the period of time until the first choice was made and led to increased movement rate on transgenic plants, and reduced fecundity on wild-type plants. Overall, our findings are consistent with the view that both performance and selectivity of B. tabaci decrease in heterogeneous habitats that contain plants with closely-related chemical signatures.     

Feeding Responses of Free-flying Honeybees to Secondary Compounds Mimicking Floral Nectars

The role of secondary compounds (SC) in deterring herbivores and pathogens from vegetative parts of plants is well established, whereas their role in plant reproductive organs such as floral nectar is unclear. The present study aimed to reveal the response of free-flying honeybees to naturally occurring concentrations of four SC in floral nectar. We selected nicotine, anabasine, caffeine, and amygdalin, all of which are found in nectar of various plants. In repeated paired-choice experiments, we offered 20% sucrose solution as control along with test solutions of 20% sucrose with various concentrations of the above SC. Except for anabasine, naturally occurring concentrations of SC did not have a deterring effect. Furthermore, low concentrations of nicotine and caffeine elicited a significant feeding preference. SC can, therefore, be regarded as postingestive stimulants to pollinators, indicating that the psychoactive alkaloids in nectar may be a part of their mutualistic reward. Further studies are needed to test our hypothesis that psychoactive alkaloids in nectar impose dependence or addiction effects on pollinators.     

Neurodevelopmental Disorders Associated with PSD-95 and Its Interaction Partners

The postsynaptic density (PSD) is a massive protein complex, critical for synaptic strength and plasticity in excitatory neurons. Here, the scaffolding protein PSD-95 plays a crucial role as it organizes key PSD components essential for synaptic signaling, development, and survival. Recently, variants in DLG4 encoding PSD-95 were found to cause a neurodevelopmental disorder with a variety of clinical features including intellectual disability, developmental delay, and epilepsy. Genetic variants in several of the interaction partners of PSD-95 are associated with similar phenotypes, suggesting that deficient PSD-95 may affect the interaction partners, explaining the overlapping symptoms. Here, we review the transmembrane interaction partners of PSD-95 and their association with neurodevelopmental disorders. We assess how the structural changes induced by DLG4 missense variants may disrupt or alter such protein–protein interactions, and we argue that the pathological effect of DLG4 variants is, at least partly, exerted indirectly through interaction partners of PSD-95. This review presents a direction for functional studies to elucidate the pathogenic mechanism of deficient PSD-95, providing clues for therapeutic strategies.     

Transversal thermal patterns in packed‐bed reactors with simple kinetics: Bifurcation criterion and simulations

We derive a new criterion for transversal instability of planar fronts based on the bifurcation condition dV_f/dK|_K=0 = 0, where V_f and K are the front velocity and its curvature, respectively. This refines our previously obtained condition, which was formulated as α = (ΔT_adPe_T)/(ΔT_mPe_C) > 1 to α > 1 + |δ|, where ΔT_ad and ΔT_m are the adiabatic and maximal temperature rise, respectively, Pe_C and Pe_T are the axial mass and the heat Pe numbers, respectively, and δ is a small parameter. The criterion is based on approximate relations for ΔT_m and V_f, which account for the local curvature of a propagating front in a packed bed reactor with a first‐order activated kinetics. The obtained relations are verified by linear stability analysis of planar fronts. Simulations of a simplified 2D model in the form of a thin cylindrical shell are in good agreement with the critical parameters predicted by dispersion relations. Three types of patterns were detected in simulations: “frozen” multiwave patterns, spinning waves, and complex rotating–oscillating patterns. We map bifurcation diagrams showing domains of different modes using the shell radius as the bifurcation parameter. The possible translation of the 2D cylindrical shell model results to the 3D case is discussed. © 2010 American Institute of Chemical Engineers AIChE J, 2011     

Hydrotreating processes for catalytic abatement of water pollutants

Opportunities and problems in application of catalytic hydrotreating processes, which are presented a viable approach in the abatement of water pollutants, are discussed. Analysis of the hydrodechlorination (HDC) and hydrodenitrification (HDN) using Pd-based catalysts supported on various materials like granulated activated carbon (GAC), fibrous activated carbon cloths (ACCs) or glass fiber cloths (GFCs) studied recently in our laboratory suggests the following perspectives:

Exhaustive regeneration of Pd/GAC saturated with p-chlorophenol can be achieved in a two-step approach, incorporating gas-phase HDC by hydrogen followed by oxidation by air.

Pd/ACC catalysts are good candidates for the liquid-phase HDC showing activity higher than that of Pd/GAC or Pd/GFC; the high adsorption capacity of Pd/ACC lead suggesting its use in a technology with periodic adsorption and HDC, in similarity to adsorption with regeneration of GAC.

Pd/GFC and Pd–Cu/GFC are promising catalyst for removal of nitrites and nitrates, showing activity and selectivity that compares favorably with those of powdered catalysts.

Characterisation of electrodeposited nanocrystalline Ni–Mo alloys

Ni–Mo nanocrystalline layers were electrodeposited using direct current from citrate–ammonia solutions. The quartz crystal microbalance investigation confirms that the discharge process starts with hydrogen evolution before the onset of the alloy deposition. The grain size was estimated from X-ray line broadening. It decreases when the molybdenum content is increased. It is smaller for layers deposited at pH 9.5 than 8.5. The microhardness exhibits a maximum close to 800 Vickers for _Mo around 17 wt%. For higher _Mo a softening is observed showing a deviation from Hall-Petch behaviour due to small grain size. In deaerated hydrochloric solutions, the layers show a large passivation domain without any pitting. The corrosion currents as well as the passivation currents, higher than for the bulk Hastelloy B alloy, decrease when _Mo is increased.     

A urine patch framework to simulate nitrogen leaching on New Zealand dairy farms

On New Zealand dairy farms, it is the nitrogen excreted directly onto pasture, particularly urine, that drives nitrogen (N) leaching from the farm. A new framework (UPF: Urine Patch Framework) is presented that post-processes the results of a whole farm model and runs a mechanistic soil model to simulate the urine patches. Two alternative methods to simulate the spatial distribution of urine patches were implemented and compared (Grid: spatially explicit, and Probabilistic: based on the probability of different temporal urination patterns). This paper describes the implementation of these two methods in connection with a Whole Farm Model; and compares the N leaching predictions with observed data. Two examples are provided, one analyzing the impact of urine patch overlap and another, the relative risk of N leaching at different times of urinary N deposition. The model showed good correlation and predictive ability between simulated annual N leaching results and observed data [R² = 94 %, mean relative prediction error (MRPE) = 10 % for Grid and R² = 72 %, MRPE = 20 % for Probabilistic]. The two methods produced similar results across an 8-year period for monthly and annual N leaching (R² = 96 %, MRPE = 10 % and R² = 86 %, MRPE = 8 %; respectively). Only 8 % of the paddock area was covered with multiple urinations during 1 year, but as much as 39 % of the total urine volume was deposited on overlapped patches. Systematically removing all urinary N for 1 month in either May or June reduced N leaching by approximately 20 %. Avoiding urinary N deposition during autumn or early winter could be highly effective in mitigating N leached during the following winter.     

The combined influence of Mg and Ca on microstructural evolution of alumina

The solubility limits of Ca and Mg co-doped in alumina at 1600°C were determined by equilibrating alumina saturated with Ca and Mg. This resulted in the formation of MgAl₂O₄ (Mg spinel), CaO·6Al₂O₃ (CA6), Ca₂Mg₂Al₂₈O₄₆ (CAM-II), and alumina grains saturated with Mg and Ca. Under these conditions, the amount of Ca and Mg in the alumina grains represents the solubility limits. The solubility limits were measured using a fully standardized wavelength dispersive spectrometer mounted on a scanning electron microscope. In the co-doped state, the solubility limit of Ca in alumina was 32 ± 13 ppm, and the solubility limit of Mg in alumina was 210 ± 43 ppm. The presence of Ca results in an increase of the solubility limit of Mg in alumina from 132 to 210 ppm, suggesting that the increased Mg in solution results in more Mg excess at the alumina grain boundaries, thus contributing to a decreased grain-boundary mobility by solute-drag.