Application of the random pore model to the carbonation cyclic reaction

Calcium oxide has been proved to be a suitable sorbent for high temperature CO₂ capture processes based on the cyclic carbonation‐calcination reaction. It is important to have reaction rate models that are able to describe the behavior of CaO particles with respect to the carbonation reaction. Fresh calcined lime is known to be a reactive solid toward carbonation, but the average sorbent particle in a CaO‐based CO₂ capture system experiences many carbonation‐calcination cycles and the reactivity changes with the number of cycles. This study applies the random pore model (RPM) to estimate the intrinsic rate parameters for the carbonation reaction and develops a simple model to calculate particle conversion with time as a function of the number of cycles, partial pressure of CO₂, and temperature. This version of the RPM model integrates knowledge obtained in earlier works on intrinsic carbonation rates, critical product layer thickness, and pore structure evolution in highly cycled particles. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

Modification of conductivity of P3HT by addition of endometallo fullerene

Germanium endometallo fullerene was synthesized by arcing Ge‐impregnated graphite rod as anode and pure graphite rod as cathode. Photoluminescence (PL) and resistance measurements suggest that there are effective interactions at the interface of Ge endometallo fullerene and poly 3‐hexyl thiophene (P3HT). Four‐fold enhancement of conductance has been found by adding just one weight percentage of Ge endometallo fullerene in the P3HT matrix at room temperature. However, at lower and higher temperatures, the enhancement in conductivity is low compared with room temperature, indicating the efficient charge transfer across the interface at the temperature range of 300–350 K. Atomic force microscopy (AFM) images also confirm the fact that temperature makes the more ordered heterojunctions between P3HT and Ge endohedral metallofullerene, which, in turn, trigger charge separation across interfaces. A sharp quenching in PL intensity of P3HT at room temperature by adding Ge endometallo fullerene indicates a strong interaction between the two and this composite material can be useful in photovoltaic cell. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Evolution of Pt and Pt-Alloy Catalytic Surfaces Under Oxygen Reduction Reaction in Acid Medium

We review our recent work that employs a series of computational techniques including density functional theory, ab initio molecular dynamics, and classical molecular dynamics to investigate changes in the structure and electronic properties of Pt-based alloy catalysts under oxygen reduction reaction conditions in acid medium. We show density-functional theory-based correlations between surface segregation and the oxidation state of the subsurface atoms, and their effects on metal dissolution. Since the onset of Pt dissolution coincides with that of surface oxidation, surface reconstruction phenomena is evaluated using ab initio and classical molecular dynamics at increasing degrees of oxidation on extended surfaces and nanoparticles, including the effects of water and an acidic solution. Significant reconstruction and compositional changes are observed as the surface is modified by the presence of adsorbates and electrolyte components. Finally we discuss the consequences of dealloying and suggest an explanation for the enhanced activity observed experimentally in the resultant nanoporous structures.     

Saccharomyces cerevisiae YCRO17c/CWH43 encodes a putative sensor/transporter protein upstream of the BCK2 branch of the PKC1-dependent cell wall integrity pathway.

The Saccharomyces cerevisiae cwh43-2 mutant, originally isolated for its Calcofluor white hypersensitivity, displays several cell wall defects similar to mutants in the PKC1-MPK1 pathway, including a growth defect and increased release of beta-1,6-glucan and beta-glucosylated proteins into the growth medium at increased temperatures. The cloning of CWH43 showed that it corresponds to YCR017c and encodes a protein with 14-16 transmembrane segments containing several putative phosphorylation and glycosylation sites. The N-terminal part of the amino acid sequence of Cwh43p shows 40% similarity with the mammalian FRAG1, a membrane protein that activates the fibroblast growth factor receptor of rat osteosarcoma (FGFR2-ROS) and with protein sequences of four uncharacterized ORFs from Caenorhabditis elegans and one from Drosophila melanogaster. The C-terminus of Cwh43p shows low similarities with a xylose permease of Bacillus megaterium and with putative sugar transporter from D. melanogaster, and has 52% similarity with a protein sequence from a Schizosaccharomyces pombe cDNA. A Cwh43-GFP fusion protein suggested a plasma membrane localization, although localization to the internal structure of the cells could not be excluded, and it concentrates to the bud tip of small budded cells and to the neck of dividing cells. Deletion of CWH43 resulted in cell wall defects less pronounced than those of the cwh43-2 mutant. This allele-specific phenotype appears to be due to a G-R substitution at position 57 in a highly conserved region of the protein. Genetic analysis places CWH43 upstream of the BCK2 branch of the PKC1 signalling pathway, since cwh43 mutations were synthetic lethal with pkc1 deletion, whereas the cwh43 defects could be rescued by overexpression of BCK2 and not by high-copy-number expression of genes encoding downstream proteins of the PKC1 pathway However, unlike BCK2, whose disruption in a cln3 mutant resulted in growth arrest in G(1), no growth defect was observed in a double cwh43 cln3 mutants. Taken together, it is proposed that CWH43 encodes a protein with putative sensor and transporter domains acting in parallel to the main PKC1-dependent cell wall integrity pathway, and that this gene has evolved into two distinct genes in higher eukaryotes.     

Variable range hopping conduction in fully dense calcium cobalt oxide textured ceramics

Fully dense hot-pressed calcium cobalt oxide (Ca₃Co₄O₉) pellet exhibits textures with Lotgering factor of unity and supports the ideally aligned (00?l), l =?2, 3, 4, 5 crystallographic planes associated in the ceramics. The DC electrical conductivity of the Ca₃Co₄O₉ pellets connected to metal/Ca₃Co₄O₉-pellet/metal device structures in vertical and lateral configurations follow Mott's variable range hopping. The exhibition of anisotropic ratio of ~ 10 between the room temperature conductivity values in both the structures, reveal the presence of partially oriented textured grains in the currently developed Ca₃Co₄O₉ ceramics.     

Computational Fluid Dynamics Study of Flow Induced by a Grooved High‐Shear Impeller in an Unbaffled Tank

A detailed hydrodynamic characterization in the transitional flow regime of two variants of the Norstone Polyblade® high‐shear impeller (HSI), of industrial relevance, is presented. The study was carried out on a simulated Newtonian fluid using computational fluid dynamics (CFD). Measurements of power number were carried out to validate the simulation results. Hydrodynamic parameters considered of key importance in powder dispersion processes (i.e., viscous dissipation and effective circulation) were used to assess the impellers' performance. Furthermore, their performances were compared with reported data for two ring‐style HSIs of two and four rings, and power number measurements of a sawtooth (Cowles‐type) impeller.     

MULTIDISCIPLINARY FLOW/THERMAL AND INDUCED STRESSES IN CONVECTIVELY COOLED STRUCTURES

A multidisciplinary finite element methodology with stabilizing features to prevent undue oscillatory solution behavior for the velocities, pressure, and temperature fields and which subsequently permits computations of the resulting thermal loads for the associated stress analysis is described for convectively cooled structures subjected to high-intensity localized heating. Of particular interest are the influences of coolants that serve to cool the structure whose exposed skin is permitted to radiate to outer space. Of the three coolants investigated - namely, liquid hydrogen, water, and liquid sodium - it is observed that the liquid sodium serves as an effective coolant that is consistent with past related studies. The resulting thermally induced stresses arising from the assumption of elastic and a materially nonlinear elastoplastic model are also evaluated. The nonlinear model seems more realistic because of the situations encountered at high temperatures and as expected yields lower values of the stresses. Illustrative examples of a flat skin structure and a curved skin geometry representing the cowl leading edge are analyzed for the flow/thermal and induced stresses.     

A population dynamics approach for the water distribution problem

The water distribution system (WDS) is composed of several elements, where flow control is one of the most important components needed in order to provide a satisfactory level of service. In order to achieve an adequate level of water in the distribution tanks, we need to dynamically control the flow. Here, we propose a population dynamics approach in order to control tanks, by allocating in them the maximum uniform volume. The feedback interconnected systems reach a stable equilibrium point for both approaches presented (i.e. replicator and supply dynamics), and more specific an asymptotically stable equilibrium point for the replicator dynamics case. The stability analysis uses some passivity concepts and classic Lyapunov theory for a closed-loop system that combines the population dynamics (controller), and the WDS (process). We show via simulations the operation under different scenarios.