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Structure Evolution (structure + evolution)
Selected AbstractsThe basidiomycete genus Polyporus , an emendation based on phylogeny and putative secondary structure of ribosomal RNA moleculesFEDDES REPERTORIUM, Issue 7-8 2004D. Krüger The fungal genus Polyporus is an assemblage of white-rotting lignicolous basidiomycetes. It has undergone considerable expansion and contraction over a period of two and three quarter centuries. Current generic circumscription of Polyporus has kept the genus non-monophyletic. Species of Polyporus infrageneric group Polyporellus are closely related to some species of Lentinus. We introduce data for ITS2 spacer rRNA secondary structure evolution by quasi-independent comparison with large subunit rRNA phylogeny, and suggest a fraction of primary nuclear rDNA ITS sequence data as novel taxonomic character. A major taxonomic shift is suggested, supported by molecular and morphological characters, and allowing inclusion of species with gilled hymenophores in Polyporus. Two new names are proposed: Polyporus phyllostipes D.Krüger, nom. nov. and Polyporus gerdai D.Krüger, nom. nov. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) Die Gattung Polyporus (Basidiomycetes) , eine Emendation auf der Basis von Phylogenie und mutmaßlicher sekundärer Struktur der ribosomalen RNA-Moleküle Die Pilzgattung Polyporus, eine Gruppe Weißfäule erregender holzbewohnender Basidiomyceten, wurde über nahezu drei Jahrhunderte vielfach expandiert und verkleinert. Bei der derzeitigen Gattungsumschreibung von Polyporus gilt die Gattung als nicht-monophyletisch. Arten der Polyporus -Gruppe Polyporellus sind eng verwandt zu einigen Lentinus- Arten. Anhand quasi-unabhängigem Vergleich mit der Phylogenie der rRNA der großen Untereinheit (LSU) stellen wir Daten zur Evolution der ITS2 Spacer rRNA vor, und schlagen ein ITS Kern-rDNA-Fragment als taxonomisches Merkmal vor. Unterstützt mit molekularen und morphologischen Daten wird eine grundlegende taxonomische Verschiebung vorgeschlagen, welche Arten mit Lamellen-Hymenophoren in Polyporus erlaubt. Zwei neue Namen werden vorgeschlagen: Polyporus phyllostipes D.Krüger, nom. nov. und Polyporus gerdai D.Krüger, nom. nov. [source] Modeling and experimental studies on combustion characteristics of porous coal char: Volume reaction modelINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 5 2010Anup Kumar Sadhukhan A generalized single-particle model for the prediction of combustion dynamics of a porous coal char in a fluidized bed is analyzed in the present work using a volume reaction model (VRM). A fully transient nonisothermal model involving both heterogeneous and homogeneous chemical reactions, multicomponent mass transfer, heat transfer with intraparticle resistances, as well as char structure evolution is developed. The model takes into account convection and diffusion inside the particle pores, as well as in the boundary layer. By addressing the Stefan flow originated due to nonequimolar mass transfer and chemical reactions, this work enables a more realistic analysis of the combustion process. The model, characterized by a set of partial differential equations coupled with nonlinear boundary conditions, is solved numerically using the implicit finite volume method (FVM) with a FORTRAN code developed in-house. The use of a FVM for solving such an elaborate char combustion model, based on the VRM, was not reported earlier. Experiments consisting of fluidized-bed combustion of a single char particle were carried out to determine the internal surface area of a partially burned char particle and to enable model validation. Predicted results are found to compare well with the reported experimental results for porous coal char combustion. The effects of various parameters (i.e., bulk temperature and initial particle radius) are examined on the dynamics of combustion of coal char. The phenomena of ignition and extinction are also investigated. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 42: 299,315, 2010 [source] Application of the random pore model to the carbonation cyclic reactionAICHE JOURNAL, Issue 5 2009Gemma Grasa Abstract 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 [source] Microstructure and Molecular Interaction in Glycerol Plasticized Chitosan/Poly(vinyl alcohol) Blending FilmsMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 10 2009Songmiao Liang Abstract Exploring some basic interactions in blending systems is of great significance for designing a blend with controlled structure and properties. This work attempts to analyze microstructure and molecular interaction in glycerol plasticized chitosan/poly(vinyl alcohol) blends by atomic force microscopy, differential scanning calorimetry and ATR-FTIR spectroscopy. Our results show that the blending films are aggregated by spherical chitosan/poly(vinyl alcohol) blending nanoparticles. The size and aggregation behavior of these particles are closely related to glycerol content. The presence of glycerol gives rise to a continuous closing in Tg of poly(vinyl alcohol) and chitosan components, suggesting an improved miscibility of the blend. Strong hydrogen bonding interaction in the blend is observed and further distinguished by peak resolution. Moreover, more interesting evidence on the effect of glycerol in the blends is provided by monitoring the structure evolution of the blend at different blending steps using atomic force microscopy. The formation of strong hydrogen bonding network among glycerol molecules and polymer matrix was considered as the main driving force to result in the changes in the microstructure and miscibility of the blend. [source] Magnetic study of Hitperm alloys (Fe0.5Co0.5)1,x ,y ,zMxByCuz (M = Hf, Zr, Nb)PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 7 2006Abstract A family of the Hitperm alloys (Fe0.5Co0.5)1,x ,y ,zMxByCuz (M = Hf, Zr, Nb) produced in an argon atmosphere as amorphous ribbons with 0.025 mm thickness are investigated up to 1200 K. The partial replacement of Fe by Co with optimal Fe0.5Co0.5 ratio increases the Curie temperature of the amorphous phase and the magnetic moment per formula unit. The early stages of crystallization can be observed by magnetization measurements. Alloys subjected to the first controlled crystallization stage are built of bcc-(Fe,Co) nanocrystals that are homegeneously embedded in the amorphous matrix. Mean grain sizes are about 11 nm. These two-phase alloys exhibit good soft magnetic properties with the relatively low coercive fields up to 50 A/m. Hafnium and hafnium/zirconium mixture are found to be the best inhibitors of the nanograin growth resulting in the best soft magnetic parameters. Alloys with niobium exhibit lower thermal stability and higher coercive fields. The correlation between the structure evolution and the magnetic properties is analysed and discussed. Conditions for optimum heat treatment are also determined. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] A new method used to control the structure of high rate microcrystalline silicon thin filmsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 3-4 2010X. D. Zhang Abstract We report a systematic study of plasma heating effect on microcrystalline silicon (,c-Si:H) deposition. Normally, substrate surface temperature increases with time during a high rate deposition of ,c-Si:H thin film, especially under a high power and high pressure condition. We deposited ,c-Si:H films using a very high frequency discharge under the high pressure and high power condition at a fixed heater temperature or a profiled heater temperature. Raman spectra with different wavelength excitations showed that a proper heater temperature profiling during ,c-Si:H deposition is an effective method to modify the structure of ,c-Si:H films, which can control the structure evolution to form a uniform crystallinity along the growth direction and reduce the amorphous incubation layer thickness (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Structural changes of hexamethylenetetramine and undecanedioic acid co-crystal (HMT-C11) as a function of the temperatureACTA CRYSTALLOGRAPHICA SECTION B, Issue 3 2003Carlos Basílio Pinheiro HMT-C11 belongs to the family of adducts formed by the co-crystallization of N4(CH2)6 molecules (hexamethylenetetramine or HMT) and aliphatic dicarboxylic acids HOOC(CH2)n, 2COOH with 5 ,n, 13 (Cn). The adducts exhibit a layered structure in which the packing between HMT and Cn is determined by strong hydrogen bonds. The compounds in this family studied so far present thermotropic structural phase transitions and, depending on the chain length, disordered, twinned and modulated phases. The structure refinement of HMT-C11 based on X-ray diffraction experiments indicates three distinct phases from the melting point down to liquid nitrogen temperature: phase I is not crystalline; phase II is disordered (stacking fault) and its average structure is described in space group Bmmb; phase III is partially disordered and its symmetry is P21/c. The systematic study of the structure evolution of phase III upon cooling revealed that the disorder has a dynamic character (anharmonicity). The main structural change observed from 293,K down to 93,K is the increase of the tilting angle of the C11 chains relative to the layer plane and the rotation of the HMT molecules. Both HMT and C11 behave like rigid bodies in the temperature range investigated. The quality of the refinements leads to a conclusive model for the O,H,N hydrogen bonds linking HMT and C11. [source] The Effect of Trivalent Cations on the Performance of Mg-M-CO3 Layered Double Hydroxides for High-Temperature CO2 CaptureCHEMSUSCHEM CHEMISTRY AND SUSTAINABILITY, ENERGY & MATERIALS, Issue 8 2010Qiang Wang Dr. Abstract The effect of trivalent cations on the performance of Mg-M-CO3 (M=Al, Fe, Ga, Mn) layered double hydroxides (LDHs) for high-temperature CO2 capture is systematically investigated for the first time. We demonstrate that the M3+ determines the structure evolution of LDH derivatives under thermal treatment, and finally influences the CO2 capture capacity. Very different calcination temperatures are required for the different LDHs to obtain their maximum CO2 capture capacities. To have a clear understanding of the reason behind these big differences the physicochemical properties, thermal stability, and memory effect of the LDHs were investigated. Both the thermal stability and the memory effect of LDHs are greatly influenced by the type of trivalent cation. The CO2 capture capacities were also evaluated under various conditions. Another important finding of this work is that the quasi-amorphous phase obtained by thermal treatment at the lowest possible temperature gives the highest CO2 capture capacity. [source] Annealed crystallization of ultrafine amorphous NiB alloy studied by XAFSJOURNAL OF SYNCHROTRON RADIATION, Issue 2 2001Shiqiang Wei XAFS has been used to investigate the local structure evolutions of ultrafine amorphous NiB alloy during the annealed crystal-lization process. A nanocrystalline Ni phase with the local structure of crystalline Ni-like and a crystalline Ni3B, have been produced for ultrafine amorphous NiB alloy under the annealed temperature of 573 K. The results rule out Rojo et al.'s devitrification mechanism of Ni80B20 amorphous alloy in which they considered that an amorphous pure Ni phase is formed in the first exothermic process. However, our results are almost identical with Riveiro et al.'s conclusion in which the intermediate state is interpreted as two metastable crystalline phases of Ni3B and Ni-rich NiB alloy. With the annealed temperature going onto 773 K, the ultrafine NiB sample is further decomposed and crystallized into crystalline Ni with long-range order. [source] | |||||||||||||