bluuebunny/crossref_metadata_2025 huggingface dataset:
Avian olfactory receptor gene repertoires: evidence for a well-developed sense of smell in birds?
Authors: Steiger Silke S , Fidler Andrew E , Valcu Mihai , Kempenaers Bart
Published: July 2008

Among vertebrates, the sense of smell is mediated by olfactory receptors (ORs) expressed in sensory neurons within the olfactory epithelium. Comparative genomic studies suggest that the olfactory acuity of mammalian species correlates positively with both the total number and the proportion of functional OR genes encoded in their genomes. In contrast to mammals, avian olfaction is poorly understood, with birds widely regarded as relying primarily on visual and auditory inputs. Here, we show that in nine bird species from seven orders (blue tit,Cyanistes caeruleus; black coucal,Centropus grillii; brown kiwi,Apteryx australis; canary,Serinus canaria; galah,Eolophus roseicapillus; red jungle fowl,Gallus gallus; kakapo,Strigops habroptilus; mallard,Anas platyrhynchos; snow petrel,Pagodroma nivea), the majority of amplified OR sequences are predicted to be from potentially functional genes. This finding is somewhat surprising as one previous report suggested that the majority of OR genes in an avian (red jungle fowl) genomic sequence are non-functional pseudogenes. We also show that it is not the estimated proportion of potentially functional OR genes, but rather the estimated total number of OR genes that correlates positively with relative olfactory bulb size, an anatomical correlate of olfactory capability. We further demonstrate that all the nine bird genomes examined encode OR genes belonging to a large gene clade, termed γ-c, the expansion of which appears to be a shared characteristic of class Aves. In summary, our findings suggest that olfaction in birds may be a more important sense than generally believed.
Summation of perceptual cues in natural visual scenes
Authors: To M , Lovell P.G , Troscianko T , Tolhurst D.J
Published: July 2008

Natural visual scenes are rich in information, and any neural system analysing them must piece together the many messages from large arrays of diverse feature detectors. It is known how threshold detection of compound visual stimuli (sinusoidal gratings) is determined by their components' thresholds. We investigate whether similar combination rules apply to the perception of the complex and suprathreshold visual elements in naturalistic visual images. Observers gave magnitude estimations (ratings) of the perceived differences between pairs of images made from photographs of natural scenes. Images in some pairs differed along one stimulus dimension such as object colour, location, size or blur. But, for other image pairs, there were composite differences along two dimensions (e.g. both colour and object-location might change). We examined whether the ratings for such composite pairs could be predicted from the two ratings for the respective pairs in which only one stimulus dimension had changed. We found a pooling relationship similar to that proposed for simple stimuli: Minkowski summation with exponent 2.84 yielded the best predictive power (
r
=0.96), an exponent similar to that generally reported for compound grating detection. This suggests that theories based on detecting simple stimuli can encompass visual processing of complex, suprathreshold stimuli.
Environmental variation at the onset of independent foraging affects full-grown body mass in the red fox
Authors: Soulsbury Carl D , Iossa Graziella , Baker Philip J , Harris Stephen
Published: July 2008

The period following the withdrawal of parental care has been highlighted as a key developmental period for juveniles. One reason for this is that juveniles cannot forage as competently as adults, potentially placing them at greater risk from environmentally-induced changes in food availability. However, no study has examined this topic. Using a long-term dataset on red foxes (Vulpes vulpes), we examined (i) dietary changes that occurred in the one-month period following the attainment of nutritional independence, (ii) diet composition in relation to climatic variation, and (iii) the effect of climatic variation on subsequent full-grown mass. Diet at nutritional independence contained increased quantities of easy-to-catch food items (earthworms and insects) when compared with pre-independence. Interannual variation in the volume of rainfall at nutritional independence was positively correlated to the proportion of earthworms in cub diet. Pre-independence cub mass and rainfall immediately following nutritional independence explained a significant proportion of variance in full-grown mass, with environmental variation affecting full-grown mass of the entire cohorts. Thus, weather-mediated availability of easy-to-catch food items at a key developmental stage has lifelong implications for the development of juvenile foxes by affecting full-grown mass, which in turn appears to be an important component of individual reproductive potential.
Trim11 modulates the function of neurogenic transcription factor Pax6 through ubiquitin–proteosome system
Authors: Tuoc Tran Cong , Stoykova Anastassia
Published: July 2008

The transcription factor Pax6 is an important developmental regulator. Spatiotemporal control of Pax6 expression during embryogenesis is crucial for regulating distinct aspects of cortical development. Here, we report that Trim11, a member of the TRIM/RBCC protein family of E3 ubiquitin ligases, interacts with Pax6 and mediates Pax6 degradation via the ubiquitin–proteasome system. Trim11 overexpression decreases endogenous Pax6 protein levels and represses Pax6 functions, including Pax6-dependent transactivation and neurogenesis. Abrogation of endogenous Trim11 expression in the developing cortex increases the level of insoluble forms of Pax6 and enhances apoptosis. We provide evidence that the B30.2 domain of Trim11 is essential for the clearance of insoluble cell proteins. Furthermore, we show that the expression of Trim11 is directly regulated by Pax6 in developing cortex in vivo. Our findings indicate that an autoregulatory feedback loop between Trim11 and Pax6 maintains a balance between the levels of Pax6 and Trim11 proteins in cortical progenitors, having an essential role for the Pax6-dependent neurogenesis.
Anterograde and retrograde amnesia of place discrimination in retrosplenial cortex and hippocampal lesioned rats
Authors: Haijima Asahi , Ichitani Yukio
Published: July 2008

Retrograde and anterograde amnesic effects of excitotoxic lesions of the rat retrosplenial cortex (RS) and hippocampus (HPC) were investigated. To test retrograde amnesia, rats were trained with two-arm place discrimination in a radial maze 4 wk and 1 d before surgery with a different arm pair, respectively. In the retention test 1 wk after surgery, both lesion groups showed temporally ungraded retrograde amnesia. To test anterograde amnesia, animals were trained after surgery to discriminate three arm pairs successively within a day, and then after interposition of 1- to 4-wk intervals, one of these pairs, respectively, was tested for retention. RS-lesioned rats could acquire these pairs of place discriminations rapidly but showed a retention interval-dependent impairment in the retention test. Conversely, HPC-lesioned rats took more sessions to acquire these pairs than did the control group, and their retention was ∼70% of correct performance regardless of retention interval. Results suggest that RS and HPC have different roles in spatial memory and that RS is important for remote memory process.
Auxin RegulatesArabidopsisAnther Dehiscence, Pollen Maturation, and Filament Elongation
Authors: Cecchetti Valentina , Altamura Maria Maddalena , Falasca Giuseppina , Costantino Paolo , Cardarelli Maura
Published: July 2008

We provide evidence on the localization, synthesis, transport, and effects of auxin on the processes occurring late in Arabidopsis thaliana stamen development: anther dehiscence, pollen maturation, and preanthesis filament elongation. Expression of auxin-sensitive reporter constructs suggests that auxin effects begin in anthers between the end of meiosis and the bilocular stage in the somatic tissues involved in the first step of dehiscence as well as in the microspores and in the junction region between anther and filament. In situ hybridizations of the auxin biosynthetic genes YUC2 and YUC6 suggest that auxin is synthesized in anthers. In agreement with the timing of auxin effects, the TIR1, AFB1, AFB2, and AFB3 auxin receptor-encoding genes are transcribed in anthers only during late stages of development starting at the end of meiosis. We found that in tir1 afb triple and quadruple mutants, anther dehiscence and pollen maturation occur earlier than in the wild type, causing the release of mature pollen grains before the completion of filament elongation. We also assessed the contribution of auxin transport to late stamen developmental processes. Our results suggest that auxin synthesized in anthers plays a major role in coordinating anther dehiscence and pollen maturation, while auxin transport contributes to the independent regulation of preanthesis filament elongation.
Arabidopsis 10-Formyl Tetrahydrofolate Deformylases Are Essential for Photorespiration
Authors: Collakova Eva , Goyer Aymeric , Naponelli Valeria , Krassovskaya Inga , Gregory Jesse F. , Hanson Andrew D. , Shachar-Hill Yair
Published: July 2008

In prokaryotes, PurU (10-formyl tetrahydrofolate [THF] deformylase) metabolizes 10-formyl THF to formate and THF for purine and Gly biosyntheses. The Arabidopsis thaliana genome contains two putative purU genes, At4g17360 and At5g47435. Knocking out these genes simultaneously results in plants that are smaller and paler than the wild type. These double knockout (dKO) mutant plants show a 70-fold increase in Gly levels and accumulate elevated levels of 5- and 10-formyl THF. Embryo development in dKO mutants arrests between heart and early bent cotyledon stages. Mature seeds are shriveled, accumulate low amounts of lipids, and fail to germinate. However, the dKO mutant is only conditionally lethal and is rescued by growth under nonphotorespiratory conditions. In addition, culturing dKO siliques in the presence of sucrose restores normal embryo development and seed viability, suggesting that the seed and embryo development phenotypes are a result of a maternal effect. Our findings are consistent with the involvement of At4g17360 and At5g47435 proteins in photorespiration, which is to prevent excessive accumulation of 5-formyl THF, a potent inhibitor of the Gly decarboxylase/Ser hydroxymethyltransferase complex. Supporting this role, deletion of the At2g38660 gene that encodes the bifunctional 5,10-methylene THF dehydrogenase/5,10-methenyl THF cyclohydrolase that acts upstream of 5-formyl THF formation restored the wild-type phenotype in dKO plants.
Study of the chemical dependence of the effective pair potentials of Co–Pt alloy
Authors: Capitan M. J. , Lefebvre S. , Calvayrac Y. , Bessiere M. , Cenedese P.
Published: July 2008

Effective pair interaction potentials of Co–Pt alloy have been obtained from X-ray diffuse scattering measurements on short-range ordered Co3Pt and Co65Pt35single crystals. The present work presents the evolution of the interaction energies in the Co–Pt alloy when the Pt concentration varies from 25 to 35 at. %. The aim of this work was to provide data in order to improve the computation of the phase diagram by allowing a concentration dependence of the effective pair potentials. Different methods have been proposed for separating the contributions of local order and first-order displacements from the total diffuse intensity. A comparison of different methods of analysis of Co3Pt diffuse-scattering intensity data is reported in the Appendix of this article; it shows that the second-order displacement terms are almost zero near the transition temperature.
Structure of Taq DNA polymerase shows a new orientation for the structure-specific nuclease domain
Authors: Urs Usha K. , Murali Ramachandran , Krishna Murthy H. M.
Published: July 2008

Thermus aquaticus DNA polymerase I consists of the polymerase, the structure-specific nuclease and the vestigial editing nuclease domains. Three-dimensional structures of the native enzyme and its complex with DNA have already been reported. The structure of a complex with an inhibitory antibody has also been determined. The structure of the native enzyme in a different crystal form determined at 2.6 Å is reported here. Optimized anomalous diffraction measurements made at the holmium L
III edge were valuable in validating solutions obtained through molecular replacement. The structure of the polymerase domain is similar to those reported previously, while the relative orientation of the structure-specific nuclease domain is significantly different from those of the native enzyme and the DNA complex; it is, however, identical to that observed in the structure of the Fab complex. In the structures of the native enzyme and of the DNA complex reported previously, the active site of the structure-specific nuclease domain is too far from that of the polymerase domain, making it difficult to propose a structural model for the in vivo primer-excision and nick-translation activities of the enzyme. In the present structure, the two active sites are considerably closer. Taken together, the reported structure of the native enzyme, that of the Fab complex and the present structure imply that the different orientation of the structure-specific nuclease domain is probably a consequence of intrinsically high relative mobility between these two domains in this enzyme.
Toward the semisynthesis of multidomain transmembrane receptors: Modification of Eph tyrosine kinases
Authors: Singla Nikhil , Himanen Juha Pekka , Muir Tom W. , Nikolov Dimitar B.
Published: July 2008

Expressed protein ligation (EPL) is a protein engineering approach that allows the modification or assembly of a target protein from multiple recombinant and synthetic polypeptides. EPL has been previously used to modify intracellular proteins and small integral membrane proteins for structural and functional studies. Here we describe the semisynthetic site‐specific modification of the complete, multidomain extracellular regions of both A and B classes of Eph receptor tyrosine kinases. We show that the ectodomains of these receptors can be ligated to different peptides under carefully established experimental conditions, while their biological activity is retained. This work extends the boundaries of the EPL technique for semisynthesis of multidomain, extracellular, disulfide‐bonded, and glycosylated proteins and highlights its potential application for reconstituting entire single‐pass transmembrane proteins.
Recombination of protein fragments: A promising approach toward engineering proteins with novel nanomechanical properties
Authors: Balamurali M.M. , Sharma Deepak , Chang Anderson , Khor Dingyue , Chu Ricky , Li Hongbin
Published: July 2008

Combining single molecule atomic force microscopy (AFM) and protein engineering techniques, here we demonstrate that we can use recombination‐based techniques to engineer novel elastomeric proteins by recombining protein fragments from structurally homologous parent proteins. Using I27 and I32 domains from the muscle protein titin as parent template proteins, we systematically shuffled the secondary structural elements of the two parent proteins and engineered 13 hybrid daughter proteins. Although I27 and I32 are highly homologous, and homology modeling predicted that the hybrid daughter proteins fold into structures that are similar to that of parent protein, we found that only eight of the 13 daughter proteins showed β‐sheet dominated structures that are similar to parent proteins, and the other five recombined proteins showed signatures of the formation of significant α‐helical or random coil‐like structure. Single molecule AFM revealed that six recombined daughter proteins are mechanically stable and exhibit mechanical properties that are different from the parent proteins. In contrast, another four of the hybrid proteins were found to be mechanically labile and unfold at forces that are lower than the ∼20 pN, as we could not detect any unfolding force peaks. The last three hybrid proteins showed interesting duality in their mechanical unfolding behaviors. These results demonstrate the great potential of using recombination‐based approaches to engineer novel elastomeric protein domains of diverse mechanical properties. Moreover, our results also revealed the challenges and complexity of developing a recombination‐based approach into a laboratory‐based directed evolution approach to engineer novel elastomeric proteins.
Helix XI contributes to the entrance of the serotonin transporter permeation pathway
Authors: Torres‐Altoro Melissa I. , White Kellie J. , Rodríguez Gustavo J. , Nichols David E. , Barker Eric L.
Published: July 2008

The sodium‐dependent transporters for dopamine, norepinephrine, and serotonin that regulate neurotransmission, also translocate the neurotoxin 1‐methyl‐4‐phenylpyridinium (MPP+). Previous studies implicated residues in transmembrane helix (TMH) XI of DAT as important sites for MPP+transport. We examined the importance of TMH XI residues F551 and F556 for MPP+translocation by human SERT. Mutations at hSERT F556, but not F551, reduced both 5‐HT and MPP+transport compared to wild type. However, F556S/hSERT showed a reduction in surface expression explaining the decrease of transport activity for 5‐HT, but did not account for the decrease in MPP+transport observed. Cysteine mutants at those positions confirmed the accessibility of hSERT/F556 to different methanethiosulfonate (MTS) reagents, suggesting its presence in a hydrophilic environment of the protein. In the presence of MTSET, current induced by 5‐HT and MPP+was inhibited at the F556C mutant. In agreement with our homology model of SERT, based on the leucine transporter (LeuTAa) fromAquifex aeolicusstructure, these results are consistent with the hypothesis that a portion of TMH XI lines the entrance into the substrate permeation pathway.
Three‐dimensional mid‐domain predictions: geometric constraints in North American amphibian, bird, mammal and tree species richness patterns
Authors: VanDerWal Jeremy , Murphy Helen T. , Lovett‐Doust Jon
Published: July 2008

The “mid‐domain effect” (MDE) has received much attention as a candidate explanation for patterns in species richness over large geographic areas. Mid‐domain models generate a central peak in richness when species ranges are placed randomly within a bounded geographic area (i.e. the domain). Until now, domain limits have been described mostly in one‐dimension, usually latitude or elevation, and only occasionally in two‐dimensions. Here we test 1‐D, 2‐D and, for the first time, 3‐D mid‐domain models and assess the effects of geometric constraints on species richness in North American amphibian, bird, mammal and tree species. Using spatially lagged simultaneous autoregressive models, empirical richness was predicted quite well by the mid‐domain predictions and the spatial autoregressive term (45–92% R2). However, our results show that empirical species richness peaks do deviate from those of the MDE predictions in 3 dimensions. Variation explained (R2) by MDE predictions generally increased with increasing mean range size of the different biotic groups (from amphibian, to tree, mammal and finally bird data), and decreased with increasing dimensions being accounted for in the models. The results suggest geometric constraints alone can explain much of the variation in species richness with elevation, specifically with respect to the larger‐range taxa, birds and mammals. Our analysis addresses many of the recent methodological criticisms directed at studies testing the MDE, and our results support the hypothesis that species diversity patterns are influenced by geometric constraints.
Parasite loads are higher in the tropics: temperate to tropical variation in a single host‐parasite system
Authors: Salkeld Daniel J. , Trivedi Mandar , Schwarzkopf Lin
Published: July 2008

Parasites are important selective forces upon the evolutionary ecology of their hosts. At least one hypothesis suggests that high species diversity in the tropics is associated with higher parasite abundance in tropical climates. Few studies, however, have directly assessed whether parasite abundance is higher in the tropics. To address this question, it is ideal, although seldom achievable, to compare parasite abundance in a single species that occurs over a geographical area including both temperate and tropical regions. We examined variation in blood parasite abundance in seven populations of a single lizard host species (Eulamprus quoyii) using a transect that spans temperate and tropical climates. Parasite prevalence (proportion of the host population infected) showed no geographical pattern. Interestingly though, parasite load was higher in lizard populations in the tropics, and was related to mean annual temperature, but not to rainfall. We speculate that in this system the relationship between latitude and parasite load is most likely due to variation in host life history over their geographic range.
Transparent, Conducting, Amorphous Oxides: Effect of Chemical Composition on Electrical and Optical Properties of Cadmium Germanates
Authors: Kikuchi Naoto , Hosono Hideo , Kawazoe Hiroshi , Oyoshi Kaiji , Hishita Shunichi
Published: July 2008

Amorphous cadmium germanate thin films with the chemical composition xCdO·(100 — x)GeO2 (}20, x, }80 mol%) were prepared by a radio‐frequency sputtering method in an ArO2 atmosphere. The electrical and optical properties of the as‐sputtered films and films after proton (H+) implantation were measured in the temperature range 300–6 K. The optical band gaps of the as‐sputtered films were 3.1 eV for all specimens; therefore, they were transparent to visible radiation. Direct‐current conductivities of all the films prepared were 10−9 S·cm−1 at room temperature. Upon proton implantation to a fluence of 2 × 1016cm−2, the conductivity of the film with x 78 at room temperature was enhanced to 210 S·cm−1, 11 orders of magnitude greater than the conductivity of the as‐sputtered film, and the conductivities remained almost constant to }6 K, whereas those of films with x, }55 remained at 10−9 S·cm−1. The carrier electron density and the mobility of carriers in the former films, both of which were evaluated from the Hall measurements, were }1 × 1020 cm−3 and 12 cm2V−1·s−1, respectively. Effects of the chemical composition on persistent photocurrents also were examined. Significant photocurrents were observed in the films with x· }50, and they were greatly enhanced in the films with x · }75. This result indicated that the bottom part of the conduction band, which was composed mainly of 5s orbitals of cadmium cations, was extended for the films with x · }75.
Microstructure Development in Al2O3‐Platelet‐Reinforced Ce‐ZrO2/Al2O3 Composites
Authors: Roeder Ryan K. , Trumble Kevin P. , Bowman' Keith J.
Published: July 2008

Composites containing Ce‐ZrO2, Al2O3, and aligned Al2O3 platelets were produced by centrifugal consolidation and pressureless sintering, followed by heat treatments at 1600°C for varied duration. Constituents in the consolidated microstructures were either uniformly distributed throughout or segregated into gradient layers, depending critically on platelet content. Quantitative image analysis was used to examine microstructure development with heat treatment. Changes in the volume fraction, dimensional anisotropy, and gradient of pores and platelets, as well as changes in the phase gradient, were quantified. Microstructure development was strongly dependent on the initial microstructure design attained from suspension processing.
High‐Resolution Electron Microscopy and Convergent‐Beam Electron Diffraction of Sintered Undoped Hydroxyapatite
Authors: Kleebe Hans‐Joachim , Brs E. F. , Bernache‐Assolant D. , Ziegler Gnter
Published: July 2008

Transmission electron microscopy (TEM) was used to characterize the microstructure of sintered undoped hydroxyapatite (OHAp). Conventional TEM observations were accom‐panied by high‐resolution electron microscopy (HREM) and convergent‐beam electron diffraction (CBED) studies. CBED analysis enabled the determination of the space group of the OHAp, P63/m. Densification of the material was performed by pressureless sintering at 1250°C for 30 min. The undoped sample was comprised of apatite as the only crystalline phase, in addition to a small volume fraction (4%) of closed porosity. In general, the observed microstructure was homogeneous and consisted of equiaxed apatite grains with an average grain diameter of }1–2μm. No indication of a residual amorphous phase, which may have formed during sintering, was observed at multigrain junctions. HREM studies on grain boundaries also revealed that no intergranular glass film was present along two‐grain junctions, indicating that densification proceeded without a liquid phase. A slightly disordered region at the interfaces was observed, suggesting an extended grain‐boundary structure.
Internal Oxidation of Ce3+‐BaTiO3 Solid Solutions
Authors: Makovec Darko , Kolar Drago
Published: July 2008

The reoxidation process in highly Ce3+‐doped BaTiO3 ceramics was studied using TEM. Samples of two different types of solid solutions, Ba1−XCe3+XTi1−X/4(VTi)X/4O3 and Ba1−XCe3+XTi4+1−XTi3+XO3, were prepared by sintering oxide mixtures in air and in a reducing atmosphere, respectively. The solid solutions were reoxidized by annealing in air at high temperatures (1000°—1100°C). As a result of internal oxidation of Ce3+ and Ti3+, fluorite CeO2 and monoclinic Ba6Ti17O40 phases were precipitated in the perovskite matrix. In Ba1−XCe3+XTi1−X/4(VTi)X/4O3 solid solution precipitates nucleate heterogeneously at grain boundaries and at extended defects inside the grains, whereas in Ba1−XCe3+XTi4+1−XTi3+XO3 solid solution precipitates are nucleated mainly homogeneously inside reoxidized perovskite grains. The form of the precipitates and their orientational relationship with the matrix, as well as the mechanism of internal oxidation, are discussed.
Ignition Phenomena and Reaction Mechanisms of the Self‐Propagating High‐Temperature Synthesis Reaction in the Titanium—Carbon—Aluminum System
Authors: Lee Wei‐Chang , Chung Shyan‐Lung
Published: July 2008

The effect of the addition of aluminum on the ignition and self‐propagating high‐temperature synthesis (SHS) reaction between titanium and carbon was experimentally investigated. Although TiC was the only product compound in the final product, the reaction between titanium and aluminum was believed to occur before the ignition of the reaction between titanium and carbon, as evidenced by a hump that appeared in the temperature profile during heating. The ignition temperature of the reaction between titanium and carbon was significantly decreased by the addition of aluminum. This was explained by the fact that the aluminum provides an easier route for reactant mass transfer, thus significantly increasing the reaction rate of the reaction between titanium and carbon. As the temperature was increased to beyond the melting point of aluminum during heating, aluminum melted and titanium dissolved into it. As the temperature was increased further (1050°C), the titanium‐containing aluminum spread over the carbon particles. Ignition is believed to have occurred by the reaction of titanium and carbon at the interface by the diffusion of titanium through the aluminum melt to the interface. The rate of heating and the density of the reactant compact also affected the ignition temperature. These were explained by their influence on the extent of the capillary spreading of the titanium‐containing aluminum melt on the carbon particles or by the formation of a TiAlx layer at the interface between the aluminum melt and the titanium particles. Fracture surfaces of the product showed three different types of morphology, i.e., discrete particles, groups of grains similar to sintered bodies, and unreacted reactant particles. A possible reaction mechanism was proposed that describes the ignition process and explains the formation of each type of product.
Interfacial Reaction of BaTiO3 Ceramics with PbO–B2O3 Glasses
Authors: Hirata Akihiko , Yamaguchi Takashi
Published: July 2008

Interfacial reactions of pure, lead‐, and zirconium‐substituted BaTiO3 ceramics with PbOB2O3 glasses were studied, with an emphasis on the effect of glass composition. Microstructures were analyzed by scanning electron microscopy and electron‐probe microanalysis aided with X‐ray diffractometry of powder mixtures in the system BaTiO3PbOB2O3 heated at 850°C. The interfacial microstructures were divided into two types, depending on the glass composition. The first type was characterized by precipitates of TiO2 dispersed in the glass matrix. Extended heating or limited glass volume resulted in the formation of a continuous layer of BaTi(BO3)2. The second type of microstructure was characterized by a lead‐rich perovskite phase, which developed at the glass/ceramic interfacial region. Growth kinetics for this phase denied the diffusion‐controlled mechanism. The substitution of lead in BaTiO3 enhanced the penetration of glass into the ceramics along the grain boundaries and developed a coreshell structure.
Coprecipitation and Hydrothermal Synthesis of Ultrafine 5.5 mol% CeO2‐2 mol% YO1.5ZrO2 Powders
Authors: Lin Jyung‐Dong , Duh Jenq‐Gong
Published: July 2008

Ultrafine 5.5 mol% CeO2—2 mol% YO1.5ZrO2 powders with controllable crystallite size were synthesized by two kinds of coprecipitation methods and subsequent crystallization treatment. The amorphous gel produced by ammonia coprecipitation and hydrothermal treatment at 200°C for 3.5 h results in an ultrafine powder with a surface area of 206 m2/g and a crystallite size of 4.8 nm. The powder produced by urea hydrolysis and calcination exhibits a purely tetragonal phase. In addition, the powders crystallized by hydrothermal treatment exhibit high packing density and can be sintered at lower temperature (,1400°C) with nearly 100% tetragonal phase achieved.
Microstructural Development of Silicon Carbide Containing Large Seed Grains
Authors: Kim Young‐Wook , Mitomo Mamoru , Hirotsuru Hideki
Published: July 2008

Fine (}0.1μm) β‐SiC powders, with 3.3 wt% large (}0.44μm) α‐SiC or β‐SiC particles (seeds) added, were hot‐pressed at 1750°C and then annealed at 1850°C to enhance grain growth. Microstructural development during annealing was investigated using image analysis. The introduction of larger seeds into β‐SiC accelerated the grain growth of elongated large grains during annealing, in which no appreciable β→α phase transformation occurred. The growth of matrix grains in materials with β‐SiC seeds was slower than that in materials with α‐SiC seeds. The material with β‐SiC seeds, which was annealed at 1850°C for 4 h, had a bimodal microstructure of small matrix grains and large elongated grains. In contrast, the material with α‐SiC seeds, also annealed at 1850°C for 4 h, had a uniform microstructure consisting of elongated grains. The fracture toughnesses of the annealed materials with α‐SiC and β‐SiC seeds were 5.5 and 5.4 MPa·1/2, respectively. Such results suggested that further optimization of microstructure should be possible with β‐SiC seeds, because of the remnant driving force for grain growth caused by the bimodal microstructure.
Dielectric Temperature Characteristics of Cerium‐Modified Barium Titanate Based Ceramics with Core—Shell Grain Structure
Authors: Park Yung , Kim Ho‐Gi
Published: July 2008

Various particle sizes of starting barium titanate were used to investigate the effect of chemical inhomogeneity on the dielectric temperature characteristics of a dilute solid solution of cerium‐modified barium titanate. Transmission electron microscopy and energy dispersive spectroscopy confirmed three distinct areas in the modified barium titanate: a grain core, a grain shell, and gradient regions. The grain size and volume fractions of the grain core were somewhat proportional to the particle size of the starting barium titanate. The dielectric temperature characteristics will be explained in the present paper in terms of the three inhomogeneous regions. Actually, the dielectric temperature characteristics of the large grains (3μm) proved to be a function of variation in the Tc values, whereas those of the small grains (,3μm) were a function of both the Tc values and the internal stress.
Laminated C‐SiC Matrix Composites Produced by CVI
Authors: Lackey W. Jack , Vaidyaraman Sundar , More Karren L.
Published: July 2008

A new type of composite, which consists of a reinforcement phase plus a matrix composed of many alternate thin layers of two different materials, has been prepared. CVI appears to be an appropriate process for the fabrication of this class of materials. We have successfully fabricated such a composite using the forced flow—thermal gradient CVI process. A carbon fibrous preform was infiltrated with alternate layers of C and SiC having thicknesses of 0.01 to 0.5μm. For a fixed cycle time, layer thicknesses increased with distance from the fiber surface. Crack deflection patterns indicate that the laminated matrix may contribute to mechanical toughness.
Elastic Properties of Laminated Calcium Aluminosilicate/Silicon Carbide Composites Determined by Resonant Ultrasound Spectroscopy
Authors: Liu Yongmei , He Yi , Chu Fuming , Mitchell Terence E. , Wadley Haydn N. G.
Published: July 2008

The elastic properties of unidirectional and 0°/90° crossply Nicalon‐SiC‐fiber‐reinforced calcium aluminosilicate (CAS/SiC) ceramic‐matrix composites have been measured using a resonant ultrasound spectroscopy (RUS) technique. This approach has allowed the nondestructive determination of the complete set of independent second‐order elastic stiffness constants of these ceramic composites. These stiffness data have been used to obtain the orientation dependence of Young's modulus and the shear modulus. The results are in reasonably good agreement with the limited experimental data obtained from mechanical testing. The RUS measurements reveal that the unidirectional CAS/SiC composite is well modeled by transverse isotropic symmetry, indicating relatively isotropic fiber spacing in the transverse plane. The analysis indicates that the overall elastic anisotropy is also small for unidirectional and 0°/90° laminated CAS ceramic‐matrix composites, a result that can be attributed to the relatively low modulus ratio of the Nicalon SiC fiber to the CAS matrix and to the moderate fiber volume fraction.
Sinter‐Forging of Nanocrystalline Zirconia: I, Experimental
Authors: Hague Douglas C. , Mayo Merrilea J.
Published: July 2008

Nanocrystalline (15 nm) yttria (3 mol%)‐stabilized zirconia (3Y‐TZP) was sinter‐forged under conditions of varying temperature (1050–1200°C), plastic strain rate (5 × 10−5 to 2 × 10−3s−1), and green density (33–48%), using constant‐crosshead‐speed tests, constant‐load (i.e., load‐and‐hold) tests, and constant‐loading‐rate tests. The densification and pore size evolution results indicate that plastic strain is largely responsible for elimination of large pores, while diffusional mechanisms control the elimination of small pores. Grain growth during sinter‐forging is observed to be dependent solely on porosity during intermediate‐stage sintering. Once the powder compact enters final‐stage sintering, however, both static (time‐ and temperature‐dependent) and dynamic (plastic‐strain‐dependent) grain growth take place, greatly accelerating the overall rate of grain growth. The use of fast strain rates to impose plastic strain before the onset of dynamic grain growth is proposed as a method of preserving small grain sizes during sinter‐forging.
Size and Charge Effects of Dopant M on the Unit‐Cell Parameters of Monoclinic Zirconia Solid Solutions Zr0.98M0.02O2 –δ(M = Ce, La, Nd, Sm, Y, Er, Yb, Sc, Mg, Ca)
Authors: Yashima Masatomo , Hirose Teruo , Kakihana Masato , Suzuki Yasuo , Yoshimura Masahiro
Published: July 2008

The crystal structure of monoclinic phase [P21/cZ= 4] has been refined by the Rietveld analysis of X‐ray powder diffraction data to study the size and charge effects of dopant Mn+on the unit‐cell parameters of monoclinic ZrO2−2 mol% MOn/2solid solutions (n= 4 for M = Ce;n= 3 for M = La, Nd, Sm, Y, Er, Yb, Sc; andn= 2 for M = Mg and Ca). For trivalent dopant (n= 3), the unit‐cell parametersam,bm,cmand unit‐cell volume increase and βmdecreases with an increase of dopant size. Unit‐cell volume increases with increasing of dopant chargen.
Hydrothermal‐Electrochemical Formation of BaTiO, Films: Electrochemical Characterization of the Early Stages of Growth
Authors: Vargas Tomás , Díaz Hugo , Silva Carmen I. , Fuenzalida Vctor M.
Published: July 2008

The formation mechanism of BaTiO, films produced by a hydrothermal‐electrochemical method was characterized using electrochemical techniques. Experiments were conducted in a three‐electrode electrochemical cell, with titanium foil as the working electrode and Ag/AgCl as the reference electrode, in a 0.25M Ba(OH)2 solution at 150°C. Hydrothermal‐electrochemical BaTiO, film formation is initially controlled by charge transfer related to the rate of electrochemical oxidation of titanium. The process later becomes mass transfer controlled, presumably related to the diffusion of Ba2+ ions across the built‐up BaTiO3 film. A relation between the mechanism of formation of BaTiO, films under both the hydrothermal‐electrochemical and the pure hydrothermal methods was established.
Preparation and Compressive Strength Behavior of Porous Ceramics with β‐Ca(PO3)2 Fiber Skeletons
Authors: Ota Yoshio , Kasuga Toshihiro , Abe' Yoshihiro
Published: July 2008

High‐strength calcium metaphosphate fibers, which are expected to show good biocompatibility, are extracted from crystallized products of ultraphosphate glasses by aqueous leaching. Porous ceramics with skeletons of β‐Ca(PO3)2 fibers for biomedical use are prepared by the sintering of the fibers. In the present work, porous ceramics having a large porosity of −70% were obtained. The compressive test of these porous ceramics showed that large strains of 0.2–0.3 are requisite for their fracture; the calcium phosphate porous ceramics in this work show much higher flexibility than conventional ceramics. The present work discusses the influence of the preparation conditions of the porous ceramics on their compressive strength behavior.
Differentiation between Pseudocubic and Cubic Phases in Y–ZrO2 Using Rietveld Analysis
Authors: Sanchez‐Bajo F. , Cachadiña Isidro , de Dios Solier Juan , Guiberteau* Fernando , Cumbrera Francisco L.
Published: July 2008

The precise microstructural characterization of the yttriapartially stabilized zirconia (Y‐PSZ) system by means of X‐ray diffractometry (XRD) experiments faces a serious challenge: the discrimination beween the cubic, c, and pseudocubic, t', phases. We show how the confusion between the two phases goes beyond a simple qualitative problem, because the relative abundances for all the present polymorphs can be substantially modified. This is particularly true for the amount of transformable tetragonal phase, which is of paramount importance for the design of zirconia‐based tough ceramics. Similarly, we show that a conclusive discrimination between c and I' phases is possible on the basis of XRD experiments by a careful application of the Rietveld method and by emphasizing some subtle details around the angular domain close to the {200} planes. The procedure is applied to samples of Y‐PSZ (4.7 mol%).
Photoacoustic Thermal Characterization of Lime‐Partially Stabilized Zirconia
Authors: Contreras Mara Eugenia , Serrato Juan , Zarate Juan , Pacheco Cuauhtemoc , Villasenor Luis
Published: July 2008

Photoacoustic and photothermal techniques are used to investigate the room‐temperature thermophysical properties of 9.4 mol% lime‐partially stabilized zirconia (Ca–PSZ) samples in the density range of 5.12 × 103−5.58 × 103 kg/m3. The open‐photoacoustic‐cell approach is used to measure thermal diffusivity, and the photothermal technique of continuous illumination of the sample in vacuum is used to measure the product of density and specific heat capacity. Thermal conductivity is shown to be the thermophysical parameter most sensitive to changes in porosity.
Synthesis of (La,Sr)MnO3–YSZ Composite Particles by Spray Pyrolysis
Authors: Fukui Takehisa , Oobuchi Takeshi , Ikuhara Yumi , Ohara Satoshi , Kodera Kaseki
Published: July 2008

(La0.8Sr0.2)0.9MnO3–YSZ composite particles were synthesized by spray pyrolysis. The mean particle size of the synthesized powders was about 1 pm and the particle size distribution was very narrow. The synthesized powders were composed of the perovskite (La,Sr)MnO3 and cubic phase YSZ. Each particle synthesized consisted of uniform and well‐dispersed line primary particles of (La,Sr)MnO3 and YSZ (0.1 μm particle size).
Fiber Coatings for SiC‐Fiber‐Reinforced BMAS Glass‐Ceramic Composites
Authors: Sun Ellen Y. , Nutt Steven R. , Brennan John J.
Published: July 2008

Interfaces in SK‐fiber‐reinforced glass‐ceramic matrix composites were modified by applying different coatings to the fibers and varying the coating thickness. Coatings of SiC/BN, Si3N4/BN, and BN were applied to the fibers by CVD prior to composite fabrication. Interfacial microstructures were characterized using high‐resolution and analytical transmission electron microscopy. Oxidation of the SiC fibers during composite fabrication was suppressed by the fiber coatings, provided that the coatings were sufficiently thick to prevent oxygen diffusion from the matrix. The SiC/RN and BN coatings were stable during high‐temperature exposures, while the Si3N4/BN coating underwent chemical reactions.
Synthesis Mechanism of an Iron–Chromium Ceramic Pigment
Authors: Escardino Agustín , Mestre Sergio , Barba Antonio , Beltrán Vicente , Blasco Antonio
Published: July 2008

The synthesis of a black Fe2O3–Cr2O3 pigment has been studied to better understand the synthesis mechanism. A mechanism is proposed according to which, under the tested operating conditions, one of the starting constituents (Cr2O3) is transferred, largely in a gas phase (after subliming), to the particle surface of the other constituent (Fe2O3), at which it is deposited or chemisorbed, forming a layer from which it diffuses inward into the Fe2O3 particles. The process stops when the composition of the resulting solid solution has become uniform.
Mechanochemical Formation of Metal–Ceramic Composites
Authors: Welham Nicholas J. , Willis Paul E. , Kerr Tony
Published: July 2008

A mechanical activation technique has been used to form composites of alumina with titanium carbide, nitride, or carbonitride, both with and without elemental iron. The composites were formed by reacting elemental aluminum with either ilmenite (FeTiO3) or rutile (TiO2) concentrates in the presence of carbon and/or nitrogen in a ball‐mill at ambient temperature. The reaction was complete for the ilmenite samples after milling but was completed only for rutile under hot pressing conditions. Microhardness measurements indicated that the composites had hardnesses in the range 19–30 GPa (1740–2750 VHN), with only a small variation within each sample. Elemental mapping of the pressed pellets indicated that titanium and aluminum were evenly distributed on a submicrometer level whereas iron tended to coalesce into <20 μm particles in the presence of TiC. The coalescence decreased with the carbon content of the hard material until iron was evenly distributed with TiN. A superstoichiometric amount of aluminum led to the formation of iron–aluminum phases which decreased the iron coalescence. The XRD crystallite size of the alumina was 30–50 nm and was 25–50 nm for the titanium phases, confirming the extremely fine microstructure.
Mechanical Properties of Strontium‐Doped Lanthanum Manganite
Authors: D'Souza Clive M. , Sammes Nigel M.
Published: July 2008

Solid oxide fuel cells that incorporate stabilized‐zirconia electrolytes commonly use the transition‐metal oxide perovskite La0.875Sr0.125MnO3+δ as the cathode. While in operation, the cathode can be subjected to significant stresses, because of thermal expansion mismatch between mating components. The mechanical behavior of La0.875Sr0.125MnO3+δ has been studied using three‐point bend strength measurements at ambient, 400°C, 800°C and 1000°C. The results show that phase transformations have an important role in the mechanical‐strength behavior. The results also indicate some unique strengthening effects that are associated with the evolution of the unit cell with temperature and the increasing symmetry of the crystal lattice.
Mullite Whiskers Grown from Erbia‐Doped Aluminum Hydroxide–Silica Gel
Authors: de Souza Milton F. , Yamamoto Jean , Regiani Inacio , Paiva‐Santos Carlos O. , de Souza Dulcina P. F.
Published: July 2008

Mullite whiskers and anisotropic grains that were derived from erbia‐doped aluminum hydroxide–silica gel were studied. Firing 3.0‐mol%‐erbia‐doped isostatically pressed pellets at 1600°C for 1.0–8.0 h resulted in a high surface concentration of mullite whiskers. Their c‐axes were aligned preferentially along the pellet surface; the maximum length was 50 μm, and the maximum aspect ratio was 23. The pellet surface was fully covered by mullite whiskers, and small anisotropic grains with a low aspect ratio were observed in the bulk. The voids that were observed in the fracture surfaces were covered fully by mullite whiskers. The large number of voids resulted in an apparent density of 1.60 g/cm3 in the sintered pellets. The molar ratio of alumina to silica in the whiskers was in the range of 1.30–1.45 (an average value of 1.31), regardless of whether the alumina/silica powder compositions were mixed in a 3:2 or 2:1 ratio.
Conventional and Microwave‐Induced Sintering Mechanisms for Reaction‐Bonded Aluminum Oxide with Zirconium Oxide Additions
Authors: Kato Masahiro , Goto Yasuhiro
Published: July 2008

Powder compacts consisting of Al, Al2O3, and ZrO2 were heated by microwave radiation. Tracing the phase evolution during reaction bonding revealed the reaction mechanism. In the case of conventional heating, the compacts expanded slightly at temperatures of <700°C due to Al surface oxidation and expanded sharply at temperatures greater than 700°C as oxidation proceeded from the surface to the interior. Then, the compacts shrank at 1550°C due to sintering. For the case of microwave heating, the compacts expanded at temperatures of <550°C due to the formation of Al3Zr. This Al3Zr formation was caused by the preferential heating of ZrO2 relative to Al and Al2O3 by microwave radiation. Then, Al3Zr was oxidized to form Al2O3 and ZrO2 at temperatures of >1000°C. Finally, the compacts shrank at 1550°C due to sintering, similarly to conventional sintering.