bluuebunny/crossref_metadata_2025 huggingface dataset:
Community Action and Research as Citizenship Construction
Authors: Montero Maritza
Published: January 2009

Social change, well‐being and liberation have been intertwined in community research and action, as much as being used as political common‐places. In this paper, it is argued that community research and action can have a political character. The epistemological premises shared by both the community and political spheres are discussed, and concepts are defined. The way community psychological action can produce changes is illustrated by an experience carried out with children from poverty sectors of Caracas, Venezuela, intended to construct citizenship by developing awareness about values, civic rights and duties, while experiencing the advantages of participation, peaceful negotiation and solidarity, during art classes. Topics regarding citizenship values and ethics were painted and discussed in a participatory way. Results about how the children developed consciousness about those topics, relating them to their lives, are presented.
Impact of epistasis and QTL×environment interaction on the accumulation of seed mass of soybean (Glycine maxL. Merr.)
Authors: HAN YINGPENG , TENG WEILI , SUN DESHENG , DU YUPING , QIU LIJUAN , XU XIANGLING , LI WENBIN
Published: January 2009

The accumulation of seed mass in soybean is affected by both genotype and environment. The aim of the present study was to measure additive, epistatic and quantitative trait locus (QTL)×environment (QE) interaction effects of QTLs on the development of 100-seed weight in a population of 143 F5derived recombinant inbred lines (RILs) developed from the cross between the soybean cultivars ‘Charleston’ and ‘Dong Nong 594’. Broad-sense heritability of 100-seed weight from 30 days (30D) to 80D stages was 0·58, 0·52, 0·62, 0·60, 0·66 and 0·57, respectively. A total of 17 QTLs with conditional additive (a) effect and/or conditional additive×environment interaction (ae) effect at specific stages were identified in ten linkage groups by conditional mapping. Of them, only 4 QTLs had significantaeffect oraeeffect at different stages of seed development. Among QTLs with significantaeffect, five acted positively and six acted negatively on seed development. A total of 35 epistatic pairwise QTLs of 100-seed weight were identified by conditional mapping at different developmental stages. Five pairs of QTL showed the additive×additive epistatic (aa) effect and 16 QTLs showed theaa×environment interaction (aae) effect at the different developmental stages. QTLs withaaeffect as well with their environmental interaction effect appeared to vary at different developmental stages. Overall, the results indicated that 100-seed weight in soybean is under developmental, genetic and environmental control.
Phylogenetic relationships and genetic diversity of the USDAVignagermplasm collection revealed by gene-derived markers and sequencing
Authors: LI WANG MING , BARKLEY NOELLE A. , GILLASPIE GRAVES A. , PEDERSON GARY A.
Published: January 2009

Phylogenetic relationships in the USDAVignagermplasm collection are somewhat unclear and their genetic diversity has not been measured empirically. To reveal interspecific phylogenetic relationships and assess their genetic diversity, 48 accessions representing 12Vignaspecies were selected, and 30 gene-derived markers from legumes were employed. Some high-quality amplicons were sequenced. Indels (insertion/deletions) were discovered from the sequence alignments that were specific identifiers for someVignaspecies. With regard to revealing polymorphisms, intron-spanning markers were more effective than exon-derived markers. These gene-derived markers were more successful in revealing interspecific polymorphisms than intraspecific polymorphisms at both the DNA fragment and sequence levels. Two different dendrograms were generated from DNA fragment data and sequence data, respectively. The results from these two dendrograms supported each other and showed similar phylogenetic relationships among theVignaspecies investigated. The accessions clustered into four main groups and 13 subgroups. Each subgroup represents a subgenus or a species. Phylogenetic analysis revealed that an accession might be misclassified in our collection. The putative misclassified accession was further supported by seed morphology. Limited intraspecific genetic diversity was revealed by these gene-derived markers and/or sequences. The USDAVignagermplasm collection currently consists of multiple species with many accessions further classified into specific subspecies, but very few subspecies of the total subspecies available exist within the collection. Based on our results, more attention should be paid to the subspecies, wild forms and/or botanical varieties for future curation in order to expand the genetic diversity ofVignagermplasm in the USDA collection.
An economic analysis of continuous positive airway pressure for the treatment of obstructive sleep apnea-hypopnea syndrome
Authors: Weatherly Helen L. A. , Griffin Susan C. , Mc Daid Catriona , Durée Kate H. , Davies Robert J. O. , Stradling John R. , Westwood Marie E. , Sculpher Mark J.
Published: January 2009

Objectives:An important option for the medical treatment of obstructive sleep apnea-hypopnea syndrome (OSAHS) is continuous positive airway pressure (CPAP) during sleep. This study reports on the cost-effectiveness of CPAP compared with dental devices and lifestyle advice. The work was commissioned by the NHS HTA Programme to inform the National Institute of Health and Clinical Excellence's (NICE) appraisal of CPAP.

Methods:A Markov model compared the interventions over the expected patient lifetime. The primary measure of cost-effectiveness was the incremental cost per quality-adjusted life-year (QALY) gained. The QALY incorporated the impact of treatments on daytime sleepiness, blood pressure and health-related quality of life (HRQoL).

Results:On average, CPAP was associated with higher costs and QALYs compared with dental devices or lifestyle advice. In the base-case analysis, the incremental cost-effectiveness ratio (ICER) for CPAP compared with dental devices was around £4,000 per QALY (2005–06 prices). The probability that CPAP is more cost-effective than dental devices or lifestyle advice at a threshold value of £20,000 per QALY was 0.78 for men and 0.80 for women. Several sensitivity analyses were undertaken and it was found that the ICER for CPAP consistently fell below £20,000 per QALY gained, apart from in a subgroup with mild disease.

Conclusions:The model suggests that CPAP is cost-effective compared with dental devices and lifestyle advice for adults with moderate or severe symptomatic OSAHS at the cost-effectiveness thresholds used by NICE. This finding is reflected in the NICE guidance.
Arthroplasty registers: A review of international experiences
Authors: Serra-Sutton Victoria , Allepuz Alejandro , Espallargues Mireia , Labek Gerold , Pons Joan M. V.
Published: January 2009

Objectives:Registers have proven to be a valuable instrument in the evaluation of arthroplasty procedures and the performance of implants. The aim of this study was to describe the structure, functioning, and content of arthroplasty registers in Europe and other parts of the world.

Methods:A search of technical reports was carried out through the Internet and in Medline/PubMed. The exhaustiveness of the information was confirmed using the links to Web pages of other registers and contacts with key people. Aims, methods in data collection and evaluation, internal structure and organization, participants, validity of the data, and other variables were assessed for each arthroplasty register using a qualitative content analysis of the texts.

Results:Fifteen arthroplasty registers were identified which published sufficient information to conduct a comparative analysis. Eight additional registers were identified but no information was available on the Internet or in English. Most registers were initiatives of an orthopaedic society receiving governmental funding. Data were collected using standardized clinical forms and additional information from clinical-administrative datasets or other registers (mortality, implant costs, hip fractures). The main outcome measure of these registers is survival of the prostheses. Registers use the Internet and their annual reports as the main strategy for the dissemination and feed-back of their results.

Conclusions:Scientific or professional societies and the public health administration should collaborate in the development of arthroplasty registers. To adequately assess the results of observational data information on the structure, the process of arthroplasty interventions and patients characteristics should be collected.
Expression de la méronymie dans les petites annonces immobilières: comparaison français/anglais/espagnol
Authors: CONDAMINES ANNE
Published: January 2009

Cet article s'intéresse aux modes d'expression de la méronymie dans les petites annonces immobilières en français/anglais/espagnol. Il met en évidence une utilisation très proche deavec, with et condans ce genre textuel, pour exprimer cette relation, et propose des pistes pour expliquer cette similarité: étymologie (la préposition introduit dans les trois langues une notion de proximité), contamination linguistique (influence entre langues), similarité de situation: nécessité de mettre en saillance un objet pour le valoriser, fonctionnement cognitif: possibilité de mettre en valeur un objet en insistant sur ses parties originales. L'étude comparative est réalisée à partir d'un corpus comportant 100 petites annonces pour chaque langue.
Computerized CBT for Adolescent Depression (“Stressbusters”) and its Initial Evaluation Through an Extended Case Series
Authors: Abeles Paul , Verduyn Chrissie , Robinson Alexander , Smith Patrick , Yule William , Proudfoot Judy
Published: January 2009

Background: “Stressbusters” is an interactive computer software programme based on a clinically effective face-to-face CBT protocol for young people with depression. It was designed for teenagers with mild to moderate depression, and comprises eight 45-minute sessions. Method: Twenty-three young people (aged 12–16; mean age 14.87 years) with symptoms of depression were recruited from CAMHS teams in Manchester and London, and received the Stressbusters treatment (range 1 – 8 sessions, mode 8 sessions). Results: On the K-SADS at initial assessment, 95% met diagnostic criteria for a depressive disorder, with a high group mean score of 35.48 (SD 9.84) on the MFQ. Post-treatment, 22% of young people met criteria for a depressive disorder, with the group mean score on the MFQ falling significantly below clinical cut-off to 20.32 (SD 11.75). These gains were maintained at 3-month follow-up. Significant improvements were also found in the adolescents' global functioning (CGAS), self-reported anxiety (RCMAS), depressive cognitions and attributions (ATQ and CTI-C), and in adolescent- and parent-reported emotional and behavioural difficulties (SDQ). Conclusions: Taken together, these results provide promising preliminary data for the clinical efficacy of Stressbusters as a valid form of CCBT for adolescents with depression.
Algorithms for representation theory of real reductive groups
Authors: Adams Jeffrey , du Cloux Fokko
Published: January 2009

The admissible representations of a real reductive groupGare known by work of Langlands, Knapp, Zuckerman and Vogan. This paper describes an effective algorithm for computing the irreducible representations ofGwith regular integral infinitesimal character. The algorithm also describes structure theory ofG, including the orbits ofK(ℂ) (a complexified maximal compact subgroup) on the flag variety. This algorithm has been implemented on a computer by the second author, as part of the ‘Atlas of Lie Groups and Representations’ project.
Influence of clouds on aerosol particle number concentrations in the upper troposphere
Authors: Weigelt A. , Hermann M. , van Velthoven P. F. J. , Brenninkmeijer C. A. M. , Schlaf G. , Zahn A. , Wiedensohler A.
Published: January 2009

This work investigates statistically the influence of clouds on aerosol particles in the upper troposphere, from the tropics to midlatitudes. More than 7500 particle concentration values, collected with the Civil Aircraft for the Regular Investigation of the Atmosphere Based on an Instrument Container, were analyzed for the occurrence of cloud contacts using backward trajectories and satellite images from the International Satellite Cloud Climatology Project. The majority of high‐altitude clouds over the Arabian Sea most likely contributed to the formation of new particles. At the contact, most clouds act as sink for Aitken and accumulation mode particles. However, as new particles grow these clouds act as indirect source for Aitken mode particles. A similar behavior was observed for clouds over the Caribbean. In contrast, no clear influence on nucleation mode particles was observed for most cloud contacts over the Middle East, southeastern Europe, and the midlatitude North Atlantic Ocean. However, in all three regions, the clouds act on average as sink for Aitken and accumulation mode particles. An analysis investigating the influence of the cloud contact duration showed that cloud contacts lasting 4 h or longer resulted in significantly higher number concentrations of nucleation and Aitken/accumulation mode particles than did short cloud contacts (1 h). This effect was observed over the Caribbean and southeastern Europe. Over the Arabian Sea, the Middle East, and the midlatitude North Atlantic Ocean, however, the duration of the cloud contact had no effect; it was only important whether a cloud contact had occurred.
Carbon nanotube electronics and photonics
Authors: Avouris Phaedon
Published: January 2009

Their geometry, mechanical flexibility, and unique charge-transport properties make carbon nanotubes ideally suited to supplant silicon in the next generation of FETs.
A DNA damage response in
Escherichia coli
involving the alternative sigma factor, RpoS
Authors: Merrikh Houra , Ferrazzoli Alexander E. , Bougdour Alexandre , Olivier-Mason Anique , Lovett Susan T.
Published: January 2009

We isolated an
Escherichia coli
mutant in the
iraD
gene, sensitive to various forms of DNA damage. Our data are consistent with the function of IraD to promote accumulation of the alternative transcription sigma factor, RpoS, by binding to the adaptor RssB protein that targets RpoS for degradation. Our results demonstrate the physiological importance of this mode of regulation for DNA damage tolerance. Although RpoS is best known for its regulation of genes induced in stationary phase, our work underscores the importance of the RpoS regulon in a DNA damage response in actively growing cells. We show that
iraD
transcription is induced by DNA damage by a mechanism independent of the SOS response. The IraD and SOS regulatory pathways appear to act synergistically to ensure survival of cells faced with oxidative or DNA damaging stress during cellular growth.
O6-methylguanine-induced cell death involves exonuclease 1 as well as DNA mismatch recognition in vivo
Authors: Klapacz Joanna , Meira Lisiane B. , Luchetti David G. , Calvo Jennifer A. , Bronson Roderick T. , Edelmann Winfried , Samson Leona D.
Published: January 2009

Alkylation-inducedO6-methylguanine (O6MeG) DNA lesions can be mutagenic or cytotoxic if unrepaired by theO6MeG-DNA methyltransferase (Mgmt) protein.O6MeG pairs with T during DNA replication, and if theO6MeG:T mismatch persists, a G:C to A:T transition mutation is fixed at the next replication cycle.O6MeG:T mismatch detection by MutSα and MutLα leads to apoptotic cell death, but the mechanism by which this occurs has been elusive. To explore how mismatch repair mediatesO6MeG-dependent apoptosis, we used anMgmt-null mouse model combined with either theMsh6-null mutant (defective in mismatch recognition) or theExo1-null mutant (impaired in the excision step of mismatch repair). Mouse embryonic fibroblasts and bone marrow cells derived fromMgmt-null mice were much more alkylation-sensitive than wild type, as expected. However, ablation of either Msh6 or Exo1 function rendered theseMgmt-null cells just as resistant to alkylation-induced cytotoxicity as wild-type cells. Rapidly proliferating tissues inMgmt-null mice (bone marrow, thymus, and spleen) are extremely sensitive to apoptosis induced byO6MeG-producing agents. Here, we show that ablation of either Msh6 or Exo1 function in theMgmt-null mouse renders these rapidly proliferating tissues alkylation-resistant. However, whereas theMsh6defect confers total alkylation resistance, theExo1defect leads to a variable tissue-specific alkylation resistance phenotype. Our results indicate that Exo1 plays an important role in the induction of apoptosis by unrepairedO6MeGs.
Seeding of Perovskite Lead Magnesium Niobate Crystallization from Pb‐Mg‐Nb‐EDTA Gels
Authors: Narendar Yeshwanth , Messing Gary L.
Published: January 2009

The addition of BaTiO3 seed particles (50 nm in diameter) to a Pb‐Mg‐Nb‐EDTA solution (where EDTA represents ethylenediamine tetraacetic acid) reduces the formation temperature from 700°C to 600°C during combustion synthesis, because of epitaxial effects. The lower perovskite formation temperature eliminates the formation of pyrochlore at the surface of the precursor bed and allows for the direct crystallization of ∼98% perovskite lead magnesium niobate (PMN) during combustion synthesis. Increasing the nucleation density of the seed particles in the seeded precursor decreases the precursor volume that is associated with each perovskite nucleus and, thus, reduces the PMN particle size from 1 µm to 0.2 µm. The influence of BaTiO3 seeding is discussed in terms of the thermodynamics of perovskite formation, the influence of BaTiO3 seed concentration, and epitaxial nucleation.
Influence of Slurry Parameters on the Characteristics of Spray‐Dried Granules
Authors: Jr. Walker William J. , Reed James S. , Verma Surendra K.
Published: January 2009

A systematic study has been performed to determine how the characteristics of granules prepared by spray drying aqueous alumina slurries are influenced by processing parameters: binder type (PEG Compound 20M or PEG‐8000), solids loading (30 or 40 vol%), ammonium polyacrylate deflocculant level (0.35‐1.00 wt%), and spray‐dryer type. Correlations between slurry rheology and granule characteristics have been made, and a model for granule formation is presented. The packing density of the primary particles within the granules is lower for slurries with higher yield stress and is dependent on the slurry solids loading. Granules prepared using 0.35 wt% deflocculant (0.14 mg/m2), which correspond to high slurry yield stress, are of solid morphology, whereas higher deflocculant levels result in hollow granules that contain a single large open pore or crater. The degree to which particles are able to rearrange during drying influences the final granule density and is determined by the strength of the floc structure, as indicated by the slurry yield stress. When the yield stress is low, a crater may form from the inward collapse of the surface of a forming granule when the particle packing density in a droplet continues to increase after the droplet size becomes fixed by the formation of a rigid shell, leaving an internal void with internal pressure lower than that of the surrounding atmosphere.
Determination of the Temperature Coefficient Distribution of Dielectric Ceramics Using Scanning Photothermal Dielectric Microscopy
Authors: Cho Yasuo , Kasahara Teruaki , Fukuda Koichi
Published: January 2009

Two‐dimensional images of the distribution showing the temperature coefficient of the dielectric constant for two types of two‐phase composite ceramics composed of TiO2‐Bi2Ti4O11 and BaTi4O9‐BaPr2Ti4O12 were obtained using scanning photothermal dielectric microscopy. The images of the TiO2‐Bi2Ti4O11 ceramic showed that the TiO2 and Bi2Ti4O11 grains had negative and positive temperature coefficients, respectively, and that the macroscopic averaged temperature coefficient of the ceramic was relatively low because of the cancellation of the opposite signs of the coefficients. On the other hand, the images of the BaTi4O9‐BaPr2Ti4O12 ceramic showed that the temperature coefficient of both grains had the same sign (negative), although their absolute values were quite different.
Fracture of Glass/Poly(vinyl butyral) (Butacite®) Laminates in Biaxial Flexure
Authors: Bennison Stephen J. , Jagota Anand , Smith C. Anthony
Published: January 2009

Glass‐polymer laminates designed as safety glazing for automotive and architectural applications demonstrate a rich variety of deformation and failure modes due to the complex stress fields developed on loading and the statistical nature of glass fracture. This complexity in stress development results from the large modulus mismatch between float glass and typical polymers used in safety glazing (Eglass/Epolymer similar/congruent 103‐105). We investigate stress development and the sequence of glass‐ply fracture in model two‐ply glass‐poly(vinyl butyral) (PVB; Butacite®) laminates during loading in biaxial flexure using a circular (upper) punch on three‐point (lower) support. The experiment is analyzed using a three‐dimensional finite‐element model with a viscoelastic constitutive model of plasticized PVB deformation. Our stress analysis shows that the maximum biaxial stress shifts location from one glass ply to the other as a function of loading rate and/or temperature and the loading‐support dimensions. We identify two primary modes for the initiation of failure associated with changes in maximum stress location: (1) first crack initiated in upper, ring‐loaded, glass ply (at the internal glass‐polymer interface) and (2) first crack initiated in lower, supported, glass ply (outer glass surface). The sequence of glass ply fracture is seen to depend strongly on loading rate and temperature: high temperatures, relative to the polymer‐glass transition temperature, and/or slow loading rates bias first cracking to the upper ply; low temperatures and/or high loading rates promote lower ply first cracking. We present a method to compute the probability of first cracking by combining our finite‐element‐based stress analysis with a Weibull statistical description of glass fracture. The test protocol and stress analysis presented can form the basis of a laboratory‐scale test for laminates and can be readily extended to describe load‐bearing capacity of laminate plates used in large‐scale commercial applications.
Characterization of Barium Titanate Powders: Barium Carbonate Identification
Authors: López Maria del Carmen Blanco , Fourlaris Georgios , Rand Brian , Riley Frank L.
Published: January 2009

A range of methods for the detection of barium carbonate contaminant in barium titanate powder has been assessed, namely: X‐ray diffraction (XRD), scanning electron microscopy (SEM), with EDS‐X‐ray microanalysis, Fourier transform infrared spectroscopy (FT‐IR), thermogravimetric analysis (TGA), gas chromatography (GC) for analysis of carbon, and X‐ray photoelectron spectroscopy (XPS). The most satisfactory procedure for the detection of the small amounts of BaCO3 commonly present is FT‐IR. Surface analyses by XPS show that the carbonate is present as a discrete phase and is not a surface film on barium titanate particles.
Neutron Diffraction and Finite‐Element Analysis of Thermal Residual Stresses on Diffusion‐Bonded Silicon Carbide‐Molybdenum Joints
Authors: Martinelli Antonio E. , Drew Robin A. L. , Fancello Eduardo A. , Rogge Ronald , Root John H.
Published: January 2009

Various approaches can be used to minimize residual stresses in ceramic‐metal joining, such as a refractory‐metal interlayer in a hot‐pressed joint. Nonetheless, it is still necessary to characterize the stresses at and near the interface between the interlayer and the ceramic, as a function of the hot‐pressing parameters. This study combines two techniques to assess the stress distribution of hot‐pressed silicon carbide‐molybdenum joints: neutron diffraction and finite‐element (FEM) analysis. The results demonstrate that the joining temperature greatly influences the final stress distribution, and that significant stress accommodation is achieved by controlling the cooling rate of the diffusion couples. FEM analysis provides a broad view of stress distribution profiles, whereas experimental stress values that are obtained via neutron diffraction allow a better assessment of the effects of parameters that are not easily reproduced using a mathematical model.
SiC Recession Caused by SiO2 Scale Volatility under Combustion Conditions: II, Thermodynamics and Gaseous‐Diffusion Model
Authors: Opila Elizabeth J. , Smialek James L. , Robinson Raymond C. , Fox Dennis S. , Jacobson Nathan S.
Published: January 2009

In combustion environments, volatilization of SiO2 to Si‐O‐H(g) species is a critical issue. Available thermochemical data for Si‐O‐H(g) species were used in the present study to calculate boundary‐layer‐controlled fluxes from SiO2. Calculated fluxes were compared to volatilization rates of SiO2 scales grown on SiC, which were measured in a high‐pressure burner rig, as reported in Part I of this paper. Calculated volatilization rates also were compared to those measured in synthetic combustion gas furnace tests. Probable vapor species were identified in both fuel‐lean and fuel‐rich combustion environments, based on the observed pressure, temperature, and velocity dependencies, as well as on the magnitude of the volatility rate. Water vapor was responsible for the degradation of SiO2 in the fuel‐lean environment. SiO2 volatility in fuel‐lean combustion environments was attributed primarily to the formation of Si(OH)4(g), with a small contribution of SiO(OH)2(g). Reducing gases such as H2 and/or CO, in combination with water vapor, contributed to the degradation of SiO2 in the fuel‐rich environment. The model to describe SiO2 volatility in a fuel‐rich combustion environment gave a less satisfactory fit to the observed results. Nevertheless, it was concluded‐given the known thermochemical data‐that SiO2 volatility in a fuel‐rich combustion environment is best described by the formation of SiO(g) at 1 atm total pressure and the formation of Si(OH)4(g), SiO(OH)2(g), and SiO(OH)(g) at higher pressures. Other Si‐O‐H(g) species, such as Si2(OH)6, may contribute to the volatility of SiO2 under fuel‐rich conditions; however, complete thermochemical data are unavailable at this time.
Relationship between Microstructure and Mechanical Performance of a 70% Silicon Nitride–30% Barium Aluminum Silicate Self‐Reinforced Ceramic Composite
Authors: Yu Feng , White Kenneth W.
Published: January 2009

The abnormal grain growth of β‐Si3N4 was observed in a 70% Si3N4–30% barium aluminum silicate (70%‐Si3N4–30%‐BAS) self‐reinforced composite that was pressureless‐sintered at 1930°C; Si3N4 starting powders with a wide particle‐size distribution were used. The addition of coarse Si3N4 powder encouraged the abnormal growth of β‐Si3N4 grains, which allowed microstructural modification through control of the content and size distribution of β‐Si3N4 nuclei. The mechanical response of different microstructures was characterized in terms of flexural strength, as well as indentation fracture resistance, at room temperature. The presence of even a small amount of abnormally grown β‐Si3N4 grains improved the fracture toughness and minimized the variability in flexural strength.
High‐Temperature Strength Behavior of Synroc‐C
Authors: Latella Bruno A. , Liu Tianshun
Published: January 2009

Comparative measurements have been made of the high‐temperature flexure strength characteristics of synroc‐C in air and argon environments. The stress–strain curves for synroc show a large deviation from linearity with increasing temperature in both environments, indicating a brittle–ductile transition. Strength is relatively constant at ≤800°C, followed by a discernible increase, with a peak at ∼920°C in air and 940°C in argon, and then a dramatic drop‐off. The strengthening response is explored with reference to microstructural changes, in particular oxidation effects, and the implications of the observations are discussed.
Influence of Cement Particle‐Size Distribution on Early Age Autogenous Strains and Stresses in Cement‐Based Materials
Authors: Bentz Dale P. , Jensen Ole Mejlhede , Hansen Kurt Kielsgaard , Olesen John F. , Stang Henrik , Haecker Claus‐Jochen
Published: January 2009

The influence of cement particle‐size distribution on autogenous strains and stresses in cement pastes of identical water‐to‐cement ratios is examined for cement powders of four different finenesses. Experimental measurements include chemical shrinkage, to quantify degree of hydration; internal relative humidity development; autogenous deformation; and eigenstress development, using a novel embedded spherical stress sensor. Because the latter three measurements are conducted under sealed conditions, whereas chemical‐shrinkage measurements are made under “saturated” conditions, the National Institute of Standards and Technology cement hydration and microstructure development model is used to separate the effects of differences in hydration rates (kinetics) from those caused by the different initial spatial arrangement of the cement particles. The initial arrangement of the cement particles controls the initial pore‐size distribution of the cement paste, which, in turn, regulates the magnitude of the induced autogenous shrinkage stresses produced by the water/air menisci in the air‐filled pores formed throughout the hydration process. The experimental results indicate that a small autogenous expansion (probably the result of ettringite formation), as opposed to a shrinkage, may be produced and early age cracking possibly avoided through the use of coarser cements.
PAC Characterization of Nontransformable Tetragonal t′ Phase in Arc‐Melted Zirconia–2.8 mol% Yttria Ceramics
Authors: Rodríguez Agustín M. , Caracoche María C. , Rivas Patricia C. , Pasquevich Alberto F. , Mintzer Sergio R.
Published: January 2009

Tetragonal compact bodies obtained by quenching from the melt a ZrO2–2.8 mol% Y2O3 commercial powder have been investigated between room temperature and 1150°C, using mainly perturbed angular correlations spectroscopy. The resulting nontransformable t′ phase observed by optical micrography is characterized at nanoscopic level by a hyperfine interaction describing defective and disordered Zr4+ neighborhoods very different from those of the regular tetragonal phase. A small amount of remaining Zr4+ sites corresponds to a scarcely distorted tetragonal structure. As the compacts are heated, two processes activate: the movement of vacancies and the gradual and irreversible conversion of t′ defective sites into less defective ones, probably resulting from oxygen absorption.
Crystallization Behavior of Sol–Gel‐Derived Strontium Barium Niobate Thin Films
Authors: Koo Junmo , Jang Jae Hyeok , Bae Byeong‐Soo
Published: January 2009

The crystallization of sol–gel‐derived strontium barium niobate (SBN) thin films on various substrates is enhanced by a two‐step heating process. Also, SBN films with c‐axis preferred orientation are obtained on MgO (100) substrates. The crystallized phase and the degree of orientation are dependent on crystallization temperature and film composition. The crystallization temperature required to form a single tetragonal tungsten bronze (TTB) SBN phase increases with an increase of Sr content due to the distorted SBN structure. However, in the case of the film on MgO substrate, the oriented crystallization which forms the single tetragonal phase occurs at a lower crystallization temperature than those of polycrystalline films because of lattice matching between the film and the substrate. Its optical and ferroelectric properties were also investigated. They vary depending on film composition, due to the effect of the distorted SBN structure.
Dislocation Loop Formation in Nonstoichiometric (Ba,Ca)TiO3 and BaTiO3 Ceramics
Authors: Suzuki Toshimasa , Ueno Mitsuo , Nishi Yuji , Fujimoto Masayuki
Published: January 2009

Dislocation loops observed in nonstoichiometric and stoichiometric (Ba,Ca)TiO3, and in stoichiometric BaTiO3 sintered in a reducing atmosphere, were characterized by conventional transmission electron microscopy (TEM) under two‐beam conditions and high‐resolution TEM atomic structure analysis. Dislocation loops mostly lay on {100} planes with Burgers vectors of type 〈100〉. The dynamic behavior of these dislocation loops during the electron beam irradiation (EBI), however, was classified into two different types of dislocation loops: in A‐site‐excess (Ba,Ca)TiO3, contrasts of dislocation loops faded completely away; in BaTiO3 and B‐site‐excess (Ba,Ca)TiO3, fine‐line contrasts remained. Dislocation loops with Burgers vectors of type 1/2〈100〉 and the resultant crystallographic shear (CS) structure with a displacement vector of type 1/2〈110〉 after EBI were proposed to interpret residual line images. Disappearance of these line images in A‐site‐excess (Ba,Ca)TiO3 strongly suggests preferential Ca ion site occupancy at the CS structure.
Discontinuous Dissolution of a Liquid Phase in Ba(Ni1/3Nb2/3)O3 Ceramics
Authors: Park Jong‐Keuk , Kim Doh‐Yeon , Yoon Duk Yong
Published: January 2009

Discontinuous dissolution of a liquid phase accompanied by diffusion‐induced grain‐boundary migration (DIGM) in Ba(Ni1/3Nb2/3)O3 (BNN) ceramics has been studied. When the liquid‐phase‐sintered BNN specimens are heat‐treated at low temperatures, the liquid phase formed during sintering is dissolved discontinuously and during the reaction grain boundaries migrate. As the heat‐treatment temperature is lowered, the degree of grain boundary migration and dissolution of the liquid phase increase. These results are qualitatively consistent with the coherency strain energy model proposed for the driving force for DIGM.
Drying and Rewetting of Mature Cement Pastes Studied through Positron Annihilation Lifetime Spectroscopy
Authors: Consolati Giovanni , Dotelli Giovanni , Quasso Fiorenza
Published: January 2009

Positron annihilation lifetime measurements have been conducted on mature cement pastes, subjected to drying and rewetting treatments that remove and restore the free water from the pastes, to study possible changes of the microstructure. Analysis of the results suggests that repeated drying followed by rewetting does not induce irreversible modifications in the configuration of the finest gel pores.
Permeable Porosity of Refractory Castables Evaluated by the Water‐Expulsion Porosimetry Technique
Authors: Innocentini Murilo D. M. , Pandolfelli Victor C.
Published: January 2009

In this work, the water‐expulsion porosimetry technique was used to quantify the permeable pores of self‐flow ultralow‐cement refractory castables that were treated at 600°–1650°C. Results have shown that the method as proposed in previous works was not valid, because water was not removed continuously from pores, relative to increased pressure. Nevertheless, the maximum pore diameter obtained according to ASTM Method E128‐89 could be successfully correlated with other castable physical properties (such as the permeability constants from the Forchheimer equation) and the apparent porosity obtained via the Archimedes technique. Although the apparent porosity decreased as the thermal treatment temperature increased, the pore morphology changed continuously, with the generation of less‐tortuous and more‐permeable paths for fluid flow.
High‐Surface‐Area Alumina Ceramics Fabricated by the Decomposition of Al(OH)3
Authors: Deng Zhen‐Yan , Fukasawa Takayuki , Ando Motohide , Zhang Guo‐Jun , Ohji Tatsuki
Published: January 2009

Al2O3‐based porous ceramics with high surface areas were fabricated by adding Al(OH)3to the starting powder, followed by pressureless sintering at temperatures >1100°C. Three types of starting powders were used in the present study: pure α‐Al2O3, α‐Al2O3+ Al(OH)3, and α‐Al2O3+ ZrO2+ Al(OH)3. The addition of Al(OH)3considerably increased the surface area of the porous Al2O3, and the addition of ZrO2further increased the surface area; a surface area as high as 36.39 m2/g was obtained, and the high surface area was retained at higher temperature. The pore size distribution of the specimens with high surface area was bimodal, with one peak at ∼100 nm and the other, which contributed most of the surface area, at ∼10 nm. X‐ray analysis showed that in the sample with the fine pores and high surface area, there was θ‐Al2O3phase produced by the decomposition of Al(OH)3, presumably because the phase transformation of θ‐Al2O3to α‐Al2O3was incomplete after low‐temperature sintering. Moreover, the porous Al2O3with high surface area retained superior mechanical properties, attributed to the good sinterability of the fine α‐Al2O3powder used in the present study. The sintered specimens could be large and designed to any shape, because pressureless sintering was used for fabrication. The present approach provides a new way of fabricating porous Al2O3ceramics that could be widely used as catalyst supports in industry, especially for high‐temperature catalysis.
Preparation of Short Mullite Fibers from Kaolin via the Addition of Foaming Agents
Authors: Li Keqin , Shimizu Tadao , Igarashi Kaoru
Published: January 2009

Short mullite fibers were fabricated by adapting the kneading–drying–calcination (KDC) process. The effect of foam forming on the formation of mullite fiber from kaolin via the KDC process, with the addition of a foaming agent, was examined. In the present study, doped sodium phosphates promoted the growth of mullite fiber and the formation of a glass matrix—effects that were ascribed to the P2O5 and Na2O components, respectively, of the sodium phosphates. In particular, the addition of sodium phosphates greatly reduced the treatment time that was required for dissolution of the glass matrix in hydrofluoric acid. The addition of 10 mass% of sodium dihydrogen phosphate and calcination at 1500°C for 10 h were the optimum conditions for a short treatment time and the formation of long fibers.
Extraction of Weibull Parameters of Fiber Strength from Means and Standard Deviations of Failure Loads and Fiber Diameters
Authors: Parthasarathy Triplicane A.
Published: January 2009

The errors in using an average fiber diameter to calculate the mean strength (ςm), Weibull reference strength (ς0), and Weibull modulus (m) from failure loads of fibers were examined experimentally. Although the use of an average diameter gave very good estimates of ςm, the error in the Weibull parameters (ς0 and m) was significant, which supported the recent simulation results. Computational approaches to reduce these errors have been considered, and a numerical procedure to extract the Weibull parameters from the means and standard deviations of the load and fiber diameter has been proven feasible, provided the sample population is large. Parametric studies have shown that sample populations of ∼175 are required to obtain results within an error of 10%. The recommended sample populations for commercial fibers are 75–200, depending on the scatter in the fiber diameter and the acceptable error.
Qualitative X‐ray Diffraction Analysis of Metastable Tetragonal (t′) Zirconia
Authors: Gibson Iain R. , Irvine John T. S.
Published: January 2009

The identification and discrimination of cubic (c) and metastable t′‐zirconia phases by conventional X‐ray diffraction has proved to be a difficult problem because of the crystallographic similarities of the two phases. In this study, the c‐phase and t′‐phase in biphasic metastable zirconia samples have been successfully distinguished by X‐ray diffraction; data were collected using a high‐resolution powder diffractometer with monochromatic radiation and the peak shapes were fitted using a peak‐fitting program to distinguish the different phases. From this study, the minimum temperature, T0, at which the t′‐phase can be obtained on cooling rapidly compositions in the range 3–7 mol% Y2O3–ZrO2 to room temperature was estimated as ∼1425°C. For a constant temperature above 1425°C, the lattice parameters of the t′‐phase of 3–7 mol% Y2O3–ZrO2 compositions within the two‐phase region of the phase diagram were unaffected by the yttria content; only the amount of t′‐phase formed was affected by the yttria content.
Microstructural Evolution during Sintering of Aluminum Nitride Ceramics Doped with Alumina and Yttria
Authors: Shirakami Tatsuya , Urabe Kazuyori , Nakano Hiromi , Meguro Takeshi , Komeya Katsutoshi , Kim Nam Heun
Published: January 2009

The microstructural evolution of AlN sintered at >1950°C was studied in a specimen doped with 10 wt% Al2O3 and 5 wt% Y2O3. The constituent phases of the specimen were AlN, YAG, γ‐AlON, and AlON polytypoids (compositional polytypes). Transmission and scanning electron microscopy revealed the microstructural characters: platelike 7AlN·Al2O3 first crystallized with concurrent formation of a residual liquid, then spherical AlN crystals formed. The liquid itself changed composition with the progress of the crystallization and reached the eutectic composition in the pseudobinary system AlN–YAG, and crystallized to an aggregate of AlN and YAG during cooling. As a product of the reaction of 7AlN·Al2O3, γ‐AlON was formed.
Improvement in Hydration Reactivity of α‐Phase Belite by Remelting Reaction
Authors: Fukuda Koichiro , Wakamatsu Norihiko , Ito Suketoshi
Published: January 2009

The hydration reactivity of the α‐phase belite, containing small amounts of Na2O, Al2O3, and Fe2O3, was significantly improved by the remelting reaction. The remelted belite, in which the reaction sufficiently occurred, was exclusively composed of the twinned β‐phase. The liquid, which was exsolved by the reaction, concentrated the Na2O component. Both the exsolved alkali and the twin boundaries accelerated the early stage of the hydration; the 2 d cumulative heat evolution of the remelted belite (∼120 J/g) was about twice that of the α‐phase belite (∼65 J/g). The grindability was also improved by the remelting reaction, which agreed with previous studies.
Effect of Activated Carbon Bed on Binder Removal from Ceramic Injection Moldings
Authors: Trunec Martin , Cihlár Jaroslav
Published: January 2009

Weight losses during the binder removal from ceramic injection moldings that have been placed in beds of activated carbon powder and two types of alumina powder were compared. The effect of the specimen size and shape on debinding in a bed of activated carbon was investigated. Because of the structure of its particles, activated carbon powder allowed binder losses in ceramic moldings that consisted of submicrometer‐sized particles to increase at a temperature of 130°C. The binder loss in a bed of activated carbon was dependent on the ratio of surface area to volume of the body that was extracted. Renewal of the sorption abilities of the bed of activated carbon after saturation with binder increased the rate of binder removal.
One‐Step Synthesis and Consolidation of Nanophase Iron Aluminide
Authors: Bernard Frédéric , Charlot Frédéric , Gaffet Eric , Munir Zuhair A.
Published: January 2009

The simultaneous synthesis and densification of nanophase iron aluminide is investigated. Elemental nanophase reactants produced by mechanical activation were reacted by field activation with the simultaneous application of uniaxial pressure. The process was demonstrated in this work by the synthesis of dense nanometric FeAl. Iron and aluminum powders were co‐milled in a specially designed planetary mill to obtain nanometric reactants and to avoid formation of any product phases. These powders were then subjected to high AC currents (1250–1500 A) and pressures in the range of 70–106 MPa. Under these conditions, a reaction was initiated and completed within a short period of time (2.5–3.5 min). XRD and energy dispersive analyses showed the product to be Fe0.515Al0.485. The relative density of the product ranged from 98.7% to 99.7%. The crystallite size of the “FeAl” intermetallic was determined by XRD line‐broadening analysis using the Williamson–Hall method. The size ranged from 32 to 89 nm and showed a dependence on lattice direction.
Effect of Heating Rates on the Synthesis of Al2O3–SiC Composites by the Self‐Propagating High‐Temperature Synthesis (SHS) Technique
Authors: Pathak Lokesh Chandra , Bandyopadhyay Debajyoti , Srikanth Srinivasan , Das Swapan Kumar , Ramachandrarao P.
Published: January 2009

Various aspects of insitu formation of Al2O3–SiC composites by the self‐propagating high‐temperature synthesis (SHS) technique have been investigated using thermal analyses (TG/DTA) of a powder mixture (4Al, 3SiO2, 3C) and pellets in an argon atmosphere at different heating rates. Both the reaction initiation and peak temperatures are found to increase with the heating rates. At lower heating rates, the powder samples do not reveal any exothermic peak possibly because of poor reactivity and sluggish exothermic reaction. The appearance of exothermic peaks in the DTA plots after melting of aluminum indicates reduction of silica by liquid aluminum. Conversion of aluminum is found to decrease marginally with an increase in heating rates. The apparent activation energy of the process compares well with the interdiffusion activation energy of silicon and oxygen, indicating that oxygen diffusion in Si formed at the reaction front may be the rate‐controlling factor for this SHS process. From SEM studies it appears that the formation of SiC whiskers is through liquid‐phase mass transfer.
Effects of Zirconium Oxide on the Reaction Bonding of Aluminum Oxide
Authors: Sheedy Paul M. , Caram Hugo S. , Chan Helen M. , Harmer Martin P.
Published: January 2009

In the reaction‐bonded aluminum oxide (RBAO) process, attrition‐milled Al/Al2O3 powder compacts are reacted in air to form Al2O3‐based ceramics. Typically, ZrO2 powder is added to control the final microstructure and properties, resulting in fine‐grained, high‐strength materials. In this study, the effects of ZrO2 on the reactivity of RBAO samples were examined using thermogravimetric analysis, X‐ray diffractometry, and other techniques. Previously, it was shown that a self‐propagating reaction could occur during firing of RBAO in air. This reaction was attributed solely to the fast and highly exothermic oxidation of the aluminum on the surface of the sample, but the results of the current study show that it is related to a reaction between aluminum and ZrO2, forming Al2O3 and Al3Zr. As a consequence, a new reaction sequence for RBAO consistent with these observations has been proposed.
Raman Study of Hi‐Nicalon‐Fiber‐Reinforced Celsian Composites: II, Residual Stress in Fibers
Authors: Gouadec Gwénaël , Colomban Philippe , Bansal Narottam P.
Published: January 2009

Band shifts in Raman spectra were used to assess, on a microscopic scale, the residual strain existing in Hi‐Nicalon silicon carbide fibers reinforcing celsian‐matrix composites. Uncoated as well as p‐BN/SiC‐coated and p‐B(Si)N/SiC‐coated Hi‐Nicalon fibers were used as the reinforcements. We unambiguously conclude that the fibers were in a state of compressive residual stress. Quantitative determination of the residual stress was made possible by taking into account the heating induced by laser probing and by using a reference line, of fixed wavenumber. We found fiber compressive residual stress values between 110 and 960 MPa, depending on the fiber/matrix coating in the composite. A stress relaxation‐like phenomenon was observed at the surface of p‐BN/SiC‐coated Hi‐Nicalon fibers whereas the uncoated or p‐B(Si)N/SiC‐coated Hi‐Nicalon fibers did not show any stress relaxation in the celsian‐matrix composites.