bluuebunny/crossref_metadata_2025 huggingface dataset:
Optical response of a ferromagnetic-diluted magnetic semiconductor hybrid structure
Authors: Redliński P. , Rappoport T. G. , Libal A. , Furdyna J. K. , Jankó B. , Wojtowicz T.
Published: March 2005

We investigate the possibility of using local magnetic fields to produce one-dimensional traps in hybrid structures for any quasiparticle possessing a spin degree of freedom. We consider a system composed of a diluted magnetic semiconductor quantum well buried below a micron-sized ferromagnetic island. A localized magnetic field is produced by a rectangular ferromagnet kept in a single domain phase. We make quantitative predictions for the optical response of the system as a function of distance between the micromagnet and the quantum well, electronic g factor, and thickness of the micromagnet.
Protein-functionalized carbon nanotube-polymer composites
Authors: Bhattacharyya S. , Sinturel C. , Salvetat J. P. , Saboungi M.-L.
Published: March 2005

We have developed fully integrated nanotube composite materials through the functionalization of multiwall carbon nanotubes (MWCNTs) by covalently attaching ferritin protein molecules onto the surface of MWCNTs. The investigation of the thermomechanical behavior was performed by dynamic mechanical thermal analysis. Results demonstrated dramatic enhancement in the mechanical properties of PVA, for example a 100%–110% increase in the modulus with the addition of 1.5 wt % of ferritin functionalized MWCNTs. Samples containing functionalized nanotubes showed a stronger influence on glass transition temperature in comparison to composites containing the same amount of nonfunctionalized nanotubes.
Seasonal fire danger forecasts for the USA
Authors: Roads J. , Fujioka F. , Chen S. , Burgan R.
Published: March 2005

The Scripps Experimental Climate Prediction Center has been making experimental, near-real-time, weekly to seasonal fire danger forecasts for the past 5 years. US fire danger forecasts and validations are based on standard indices from the National Fire Danger Rating System (NFDRS), which include the ignition component (IC), energy release component (ER), burning index (BI), spread component (SC), and the Keetch–Byram drought index (KB). The Fosberg fire weather index, which is a simplified form of the BI, has been previously used not only for the USA but also for other global regions and is thus included for comparison. As will be shown, all of these indices can be predicted well at weekly times scales and there is even skill out to seasonal time scales over many US West locations. The most persistent indices (BI and ER) tend to have the greatest seasonal forecast skill. The NFDRS indices also have a weak relation to observed fire characteristics such as fire counts and acres burned, especially when the validation fire danger indices are used.
Smoke measurements during Gestosa-2002 experimental field fires
Authors: Miranda A. I. , Ferreira J. , Valente J. , Santos P. , Amorim J. H. , Borrego C.
Published: March 2005

Currently, there is a growing awareness that smoke produced during forest fires can expose individuals and populations to hazardous concentrations of air pollutants. Aiming to contribute to a better understanding of the air pollution phenomenon associated with forest fires, this paper presents and analyses the atmospheric emissions and air quality concentration measurements performed in the 2002 fire experiments at Gestosa, Central Portugal. Two vehicles were equipped with a meteorological station and air quality analysers that were turned on continuously to acquire concentrations of particulate matter, nitrogen oxides and carbon monoxide. Nitrogen and sulfur dioxides were measured using a grid of fixed passive samplers. Also, firefighters and research-team members used passive samplers during the experiments in order to estimate the human exposure to these pollutants. Measurements of volatile organic compound emissions, using Tedlar bags, were carried out. Results were analysed taking into account not only the concentration values but also the variables involved, such as the combustion phase and the meteorology, and identifying possible relationships between them. Despite the small size of the burning plots when compared to wildfires, the measured levels of pollutants were however considerable, indicating the effect of these experiments on the local air quality and stressing the serious levels of air pollution that can be expected during wildfires.
Site-directed spin labeling reveals a conformational switch in the phosphorylation domain of smooth muscle myosin
Authors: Nelson Wendy D. , Blakely Sarah E. , Nesmelov Yuri E. , Thomas David D.
Published: March 2005

We have used site-directed spin labeling and EPR spectroscopy to detect structural changes within the regulatory light chain (RLC) of smooth muscle myosin upon phosphorylation. Smooth muscle contraction is activated by phosphorylation of S19 on RLC, but the structural basis of this process is unknown. There is no crystal structure containing a phosphorylated RLC, and there is no crystal structure for the N-terminal region of any RLC. Therefore, we have prepared single-Cys mutations throughout RLC, exchanged each mutant onto smooth muscle heavy meromyosin, verified normal regulatory function, and used EPR to determine dynamics and solvent accessibility at each site. A survey of spin-label sites throughout the RLC revealed that only the N-terminal region (first 24 aa) shows a significant change in dynamics upon phosphorylation, with most of the first 17 residues showing an increase in rotational amplitude. Therefore, we focused on this N-terminal region. Additional structural information was obtained from the pattern of oxygen accessibility along the sequence. In the absence of phosphorylation, little or no periodicity was observed, suggesting a lack of secondary structural order in this region. However, phosphorylation induced a strong helical pattern (3.6-residue periodicity) in the first 17 residues, while increasing accessibility throughout the first 24 residues. We have identified a domain within RLC, the N-terminal phosphorylation domain, in which phosphorylation increases helical order, internal dynamics, and accessibility. These results support a model in which this disorder-to-order transition within the phosphorylation domain results in decreased head–head interactions, activating myosin in smooth muscle.
Cap-binding protein 1-mediated and eukaryotic translation initiation factor 4E-mediated pioneer rounds of translation in yeast
Authors: Gao Qinshan , Das Biswadip , Sherman Fred , Maquat Lynne E.
Published: March 2005

Nonsense-mediated mRNA decay (NMD) in mammalian cells is restricted to newly synthesized mRNA that is bound at the 5′ cap by the major nuclear cap-binding complex and at splicing-generated exon–exon junctions by exon junction complexes. This messenger ribonucleoprotein has been called the pioneer translation initiation complex and, accordingly, NMD occurs as a consequence of nonsense codon recognition during a pioneer round of translation. Here, we characterize the nature of messenger ribonucleoprotein that is targeted for NMD in
Saccharomyces cerevisiae
. Data indicate that NMD targets both cap-binding complex (Cbc)1p- and eukaryotic translation initiation factor (eIF)4E-bound mRNAs, unlike in mammalian cells, where NMD does not detectably target eIF4E-bound mRNA. First, intron-containing pre-mRNAs in yeast are detectably bound by either Cbc1p, or, unlike in mammalian cells, eIF4E, indicating that mRNAs can be derived from either Cbc1p- or eIF4E-bound pre-mRNAs. Second, the ratio of nonsense-containing Cbc1p-bound mRNA to nonsense-free Cbc1p-bound mRNA, which was < 0.4 for those mRNAs tested here, is essentially identical to the ratio of the corresponding nonsense-containing eIF4E-bound mRNA to nonsense-free eIF4E-bound mRNA, and both ratios increase in cells treated with the translational inhibitor cycloheximide (CHX). These data, together with data presented here and elsewhere showing that Cbc1p-bound transcripts are precursors to eIF4E-bound transcripts, demonstrate that Cbc1p-bound mRNA is targeted for NMD. In support of the idea that eIF4E-bound mRNA is also targeted for NMD, eIF4E-bound mRNA is targeted for NMD in strains that lack Cbc1p. These results suggest that both Cbc1p- and eIF4E-mediated pioneer rounds of translation occur in yeast.
Meiotic and epigenetic defects in Dnmt3L-knockout mouse spermatogenesis
Authors: Webster Kylie E. , O'Bryan Moira K. , Fletcher Stephen , Crewther Pauline E. , Aapola Ulla , Craig Jeff , Harrison Dion K. , Aung Hnin , Phutikanit Nawapen , Lyle Robert , Meachem Sarah J. , Antonarakis Stylianos E. , de Kretser David M. , Hedger Mark P. , Peterson Pärt , Carroll Bernard J. , Scott Hamish S.
Published: March 2005

The production of mature germ cells capable of generating totipotent zygotes is a highly specialized and sexually dimorphic process. The transition from diploid primordial germ cell to haploid spermatozoa requires genome-wide reprogramming of DNA methylation, stage- and testis-specific gene expression, mitotic and meiotic division, and the histone–protamine transition, all requiring unique epigenetic control. Dnmt3L, a DNA methyltransferase regulator, is expressed during gametogenesis, and its deletion results in sterility. We found that during spermatogenesis, Dnmt3L contributes to the acquisition of DNA methylation at paternally imprinted regions, unique nonpericentric heterochromatic sequences, and interspersed repeats, including autonomous transposable elements. We observed retrotransposition of an LTR-ERV1 element in the DNA from
Dnmt3L
–/
–
germ cells, presumably as a result of hypomethylation. Later in development, in
Dnmt3L
–/–
meiotic spermatocytes, we detected abnormalities in the status of biochemical markers of heterochromatin, implying aberrant chromatin packaging. Coincidentally, homologous chromosomes fail to align and form synaptonemal complexes, spermatogenesis arrests, and spermatocytes are lost by apoptosis and sloughing. Because Dnmt3L expression is restricted to gonocytes, the presence of defects in later stages reveals a mechanism whereby early genome reprogramming is linked inextricably to changes in chromatin structure required for completion of spermatogenesis.
Genome-wide analysis of cAMP-response element binding protein occupancy, phosphorylation, and target gene activation in human tissues
Authors: Zhang Xinmin , Odom Duncan T. , Koo Seung-Hoi , Conkright Michael D. , Canettieri Gianluca , Best Jennifer , Chen Huaming , Jenner Richard , Herbolsheimer Elizabeth , Jacobsen Elizabeth , Kadam Shilpa , Ecker Joseph R. , Emerson Beverly , Hogenesch John B. , Unterman Terry , Young Richard A. , Montminy Marc
Published: March 2005

Hormones and nutrients often induce genetic programs via signaling pathways that interface with gene-specific activators. Activation of the cAMP pathway, for example, stimulates cellular gene expression by means of the PKA-mediated phosphorylation of cAMP-response element binding protein (CREB) at Ser-133. Here, we use genome-wide approaches to characterize target genes that are regulated by CREB in different cellular contexts. CREB was found to occupy ≈4,000 promoter sites
in vivo
, depending on the presence and methylation state of consensus cAMP response elements near the promoter. The profiles for CREB occupancy were very similar in different human tissues, and exposure to a cAMP agonist stimulated CREB phosphorylation over a majority of these sites. Only a small proportion of CREB target genes was induced by cAMP in any cell type, however, due in part to the preferential recruitment of the coactivator CREB-binding protein to those promoters. These results indicate that CREB phosphorylation alone is not a reliable predictor of target gene activation and that additional CREB regulatory partners are required for recruitment of the transcriptional apparatus to the promoter.
Big Ideas for a Small Town: the Huddersfield Creative Town Initiative
Authors: Wood Phil , Taylor Calvin
Published: March 2005

Whilst much of the attention of those concerned with culture and regeneration has rightly been focused upon the core cities and regional capitals, it would be a mistake to assume that smaller towns and cities do not also have a role to play. Huddersfield, West Yorkshire, is one of a number of towns clustered around the Pennines that grew, and for a hundred years prospered, from the textile trade but which, by the 1980s, were in serious economic decline. This article examines how culture has contributed to the regeneration of the town and the wider local authority district. It reviews the developing role of the creative industries within the district and, in particular, the role of the local Council as a key catalyst for many of the institutional and policy shifts that have contributed to this development. The paper is very much intended as reflection on a particular case study. It is certainly not offered as a blueprint but as an opportunity to contribute to the developing knowledge base concerned with the role of the cultural and creative industries in urban development.
Political economies & the study of Africa: Critical considerations
Authors: Williams Gavin
Published: March 2005

This paper is a revised version of a keynote address to the Review of African Political Economy Conference in Birmingham on 5 September 2003. It situates the contributions of the Review of African Political Economy to understanding Africa in relation to the defining texts of political economy and economic science and of political domination. It rejects culturalist, rationalist and causal explanations of African societies in favour of historical analyses. It argues for the importance of studies of Africa for the historical and social sciences. It considers the conditions necessary to create and sustain democratic citizenship. It questions the idea of ‘development’ and argues for the need to examine ‘really-existing policies’. It follows Max Weber in contrasting the conflicting responsibilities of political action and scientific enquiry.
Comparison of climate space and phylogeny of
Marmota
(Mammalia: Rodentia) indicates a connection between evolutionary history and climate preference
Authors: Davis Edward Byrd
Published: March 2005

Palaeobiologists have investigated the evolutionary responses of extinct organisms to climate change, and have also used extinct organisms to reconstruct palaeoclimates. There is evidence of a disconnection between climate change and evolution that suggests that organisms may not be accurate palaeoclimate indicators. Here, marmots (
Marmota
sp.) are used as a case study to examine whether similarity of climate preferences is correlated with evolutionary relatedness of species. This study tests for a relationship between phylogenetic distance and `climate distance' of species within a clade. There should be a significant congruence between maximum likelihood distance and standardized Euclidian distance between climates if daughter species tend to stay in environments similar to parent species. Marmots make a good test case because there are many extant species, their phylogenies are well established and individual survival is linked to climatic factors. A Mantel test indicates a significant correlation between climate and phylogenetic distance matrices, but this relationship explains only a small fraction of the variance (regression
R
2
=0.114). These results suggest that (i) closely related species of marmots tend to stay in similar environments; (ii) marmots may be more susceptible than many mammals to global climate change; and (iii) because of the considerable noise in this system, the correlation cannot be used for detailed palaeoclimate reconstruction.
Orientation in the wandering albatross: interfering with magnetic perception does not affect orientation performance
Authors: Bonadonna F , Bajzak C , Benhamou S , Igloi K , Jouventin P , Lipp H.P , Dell'Omo G
Published: March 2005

After making foraging flights of several thousands of kilometres, wandering albatrosses (Diomedea exulans) are able to pinpoint a specific remote island where their nests are located. This impressive navigation ability is highly precise but its nature is mysterious. Here we examined whether albatrosses rely on the perception of the Earth's magnetic field to accomplish this task. We disturbed the perception of the magnetic field using mobile magnets glued to the head of nine albatrosses and compared their performances with those of 11 control birds. We then used satellite telemetry to monitor their behaviour. We found that the ability of birds to home to specific nest sites was unimpaired by this manipulation. In particular, experimental and control birds did not show significant differences with respect to either foraging trip duration, or length, or with respect to homing straightness index. Our data suggest that wandering albatrosses do not require magnetic cues to navigate back to their nesting sites.
Melnikov Analysis for a Singularly Perturbed DSII Equation
Authors: Li Y. Charles
Published: March 2005

Rigorous Melnikov analysis is accomplished for Davey–Stewartson II equation under singular perturbation. Unstable fiber theorem and center‐stable manifold theorem are established. The fact that the unperturbed homoclinic orbit, obtained via a Darboux transformation, is a classical solution, leads to the conclusion that only local well posedness is necessary for such a Melnikov analysis. The main open issue regarding a proof of the existence of a homoclinic orbit to the perturbed Davey–Stewartson II equation is discussed in the Appendix.
Evaluation of surgical margins in melanocytic lesions: a survey among 152 dermatopathologists
Authors: Sellheyer Klaus , Bergfeld Wilma F. , Stewart Emily , Roberson Gerald , Hammel Jeffrey
Published: March 2005

Background:  Although guidelines are established for reporting tissue specimens of melanomas, such guidelines are not available for reporting surgical margins of benign melanocytic lesions.

Methods:  We surveyed 582 members of the American Society of Dermatopathology via a web‐based questionnaire to evaluate the practice of reporting surgical margins in melanocytic lesions. We were especially interested if the evaluation of margins differs depending on the surgical technique used (shave, punch, and excision) and on the type of melanocytic lesion encountered.

Results:  One hundred and fifty‐two surveys (26.1%) were returned. Only 32.2% of the dermatopathologists comment routinely on margins of shaved melanocytic nevi and only 33.6% report margins in punch biopsies. More dermatopathologists (57.2%) routinely evaluate excision specimens of melanocytic nevi for margins but still almost half of the survey participants do not report margins in such a common clinical scenario. In contrast, routine evaluation for margins in excised melanomas is high (93.4%). Participants who use the terminology of dysplastic nevi evaluate margins more often and the reporting correlates with the degree of dysplasia. Asked for the terminology used to comment on surgical margins in melanocytic lesions, we observed a great variability in language.

Conclusions:  Although clinicians commonly request margin evaluation in melanocytic lesions, dermatopathologists often seem to be reluctant to do so depending on the type of procedure used to remove the lesion. There is a great variability in practice and terminology of when and how to report surgical margins in melanocytic skin lesions.
Thermal Expansion Behavior of NaZr2(PO4)3Type Compounds
Authors: OOTA TOSHITAKA , YAMAI IWAO
Published: March 2005

The thermal expansion of the skeletal framework was essentially zero for NaZr2(PO4)3‐type compounds; the interstitialion, e.g., Na+, was primarily responsible for the total thermal expansion. The composition dependence of the thermal expansion is discussed in terms of the amounts, crystallographic sites, and ionic radii of the interstitial ions. The mechanism which results in low thermal expansion was clarified, particularly for KZr2(PO4)3, in which a larger ion is substituted for Na+, and NbZr(PO4)3, which does not contain Na+. Polycrystalline ceramics formed from these crystals might be useful as thermal‐shock‐resistant materials.
Laser Technique for Evaluating Spall Resistance of Brittle Coatings
Authors: LOH R. L. , ROSSINGTON C. , EVANS A. G.
Published: March 2005

A laser technique for evaluating the spall resistance of brittle coatings was demonstrated. The method utilizes laser heating to motivate the spall by generating compressive stress in the coating. Critical exposure to laser heating thereby causes spalling at defective regions of the coating (nondefective regions are apparently immune to spalling). The laser spall results were calibrated against indentation tests in conjunction with a spalling criterion based on a critical bending strain.
Alkoxide Precursor Synthesis and Characterization of Phases in the Barium‐Titanium Oxide System
Authors: RITTER J. J. , ROTH R.S. , BLENDELL J. E.
Published: March 2005

Barium titanate precursors with Ba/Ti ratios ranging from 2:1 to 1:9 were prepared by controlled hydrolysis of mixed barium and titanium species in an alcohol medium. Details of the synthesis and characterization of the resultant products are given. Amorphous powders precipitated by hydrolysis from ethanol solutions of barium and titanium alkoxides crystallize to single‐or two‐phase 1:2 and 1:5 compounds at ∼700°C. These compounds transform at higher temperatures to other known crystalline phases, the 1:5 phase being maintained metastably to ∼1100°C.
Redox Characterization of Simulated Nuclear Waste Glass
Authors: GOLDMAN D.S. , BRITE D. W.
Published: March 2005

Ferrous/ferric equilibria were determined in an alkali‐iron borosilicate glass of the type that is presently being considered for nuclear waste disposal. Theoretical redox behavior is found at conditions more reducing than 1 kPa. Deviation from this behavior at more oxidizing conditions results from mutual interactions between the iron redox couple and other multivalentions in the glass. The results suggest that the ferrous/ferric ratio can be used as a quantitative indicator of the glass oxidation state in these complex glasses. Implications regarding redox control of the vitrification process are discussed.
Carbonate Associated with Hydroxide Sol‐Gel Processing of Yttria:. An Infrared Spectroscopic Study
Authors: SEAVERSON L.M. , LUO S.‐Q. , CHIEN P.‐L. , McCLELLAND J.F.
Published: March 2005

Yttrium hydroxide gel was dried by five techniques to study their influences on the sintering behavior of yttria. Dried precursors, calcined and sintered oxides, and the initial gel were examined via Fourier transform infrared photoacoustic and/or attenuated total reflection spectroscopies. Carbonate was found to be in unidentate coordination to surface yttrium on both the dried hydroxide precursor and calcined oxide particles. An inverse correlation was found between the normalized surface carbonate concentration (carbonate concentration (wt%)/surface area (m2/g) of precursors and calcined oxides and the density of their corresponding sintered bodies. Carbonate affects sintered density during the calcination and sintering steps.
Morphology of Tetragonal Precipitates in Partially Stabilized ZrO2
Authors: LANTERI V. , MITCHELL T. E. , HEUER A. H.
Published: March 2005

Tetragonal (t) ZrO2 precipitates in Mg‐, Ca‐, and Y‐partially‐stabilized ZrO2 (Mg‐PSZ, Ca‐PSZ, Y‐PSZ) have different habit planes and different morphologies. These differences arise because of differences in lattice parameters of precipitate and cubic (c) ZrO2 matrix in the three systems. The approximate {001} habit plane and oblate spheroid precipitate morphology observed in Mg‐PSZ are explained in terms of anisotropic elasticity using the theory of Khachaturyan. The aspect ratio of ∼5 of these particles is used to calculate a c/t interfacial energy of ∼0.15 J·m–2. The aligned equiaxed precipitates observed in Ca‐PSZ and the twinned colonies observed in Y‐PSZ can also be explained using this theory and arise from interactions between strain fields during coarsening; the aligned particles in Ca‐PSZ may actually represent an intermediate state before the formation of colonies in this system.
31P and 29Si Magic‐Angle Sample‐Spinning NMR Investigation of the Structural Environment of Phosphorus in Alkaline‐Earth Silicate Glasses
Authors: Yang Wang‐Hong , Kirkpatrick R. James , Turner Gary
Published: March 2005

29Si and 31P magic‐angle sample‐spinning NMR spectroscopy indicates that phosphorus added as P2O5 to alkaline‐earth metasilicate glasses is present as monomeric (PO4)3– structural units and that incorporation of this phosphorus increases the average polymerization of the silicate portion of the glass. These results are consistent with published interpretations of Raman spectra of similar composition.
Activation Enthalpy for Diffusion in Glass
Authors: McElfresh DavidK. , Howitt Dvid G.
Published: March 2005

Foe nearly three decades people have employed an equation derived by Frenkel to describe the strain energy of an atom diffusing in a glass. This equation describes the strain energy to enlarge a spherical cavity and predicts physically unreasonable results. An alternative equation for a circularly symmetric enlargement is presented which is a more representative geometry and does not lead to these inconsistencies.
Characterization of Spinel Phase Formed in the Kaolin‐Mullite Thermal Sequence
Authors: Okada Kiyoshi , ŌTsuka Nozomu , Ossaka Joyo
Published: March 2005

The spinel phase formed on the thermal reaction of kaolin group minerals was characterized by X‐ray quantitative analysis, lattice constant determination, and chemical analysis by analytical TEM. The spinel phase was determined to be nearly γ‐Al2O3 with ∼8 wt% of SiO2, significantly less than previously reported.
Solubility of TiO2 in ZrO2
Authors: Bannister Michael J. , Barnes Judith M.
Published: March 2005

The solubility of TiO2 in tetragonal ZrO2 is 13.8±0.3 mol% ui 1300°C, 14.9±0.2 mol% at 1400°C, and 16.1±0.2 mol% at 1500°C. These solid solutions transform to metastable monoclinic solid solutions without compositional change on cooling to room temperature.
Two R Curves for Partially Stabilized Zirconia
Authors: ROSE L. R. F. , SWAIN M. V.
Published: March 2005

The enhanced fracture toughness due to stress‐induced transformation can be explained from two viewpoints: (1) the increase can be attributed to the need to supply a work of transformation, or (2) the transformation can be considered to result in internal stresses which oppose crack opening. Experimental results for magnesia‐partially‐stabilized zirconia are presented for the two experimental measures of toughness corresponding to these two viewpoints, namely (1) the specific work of fracture, R, and (2) the nominal stress intensity factor, KR. It is observed that these two measures are not equivalent during the initial stage of R‐curve behavior, prior to reaching steady‐state cracking. The theoretical reason for this difference is discussed. In particular, it is noted that the usual definition for the crack extension force does not correspond to the experimentally measured work of fracture in the presence of stress‐induced (or pre‐existing) sources of internal stress.
Grain‐Boundary Effect in Ceria Doped with Trivalent Cations: I, Electrical Measurements
Authors: GERHARDT R. , NOWICK A. S.
Published: March 2005

The “grain‐boundary effect,” which leads to a greatly reduced dc ionic conductivity due to the presence of a blocking layer in the vicinity of the grain boundaries, is studied in detail for ceria ceramics doped with various trivalent dopants (particularly Y3+, Gd3+, and La3+). The effects of porosity, of sintering time, and of dopant size and dopant concentration are investigated. Finally, it is shown that the grain‐boundary effect virtually disappears when nearly silicon‐free starting materials are used.
Nonstoichiometric K2NiF4‐Type Phases in the Lanthanum‐Cobalt‐Oxygen System
Authors: LEWANDOWSKI JOSEPH T. , BEYERLEIN ROBERT A. , LONGO JOHN M. , McCAULEY RONALD A.
Published: March 2005

The K2NiF4‐type phase in the La‐Co‐O system has been studied and vacancy formation on both the lanthanum and oxygen sublattices has been observed. The formula La2CoO4 has generally been accepted for the K2NiF4‐type phase in the La‐Co‐O system. However, a broad range of lattice constants are reported for this material, indicative of variations in composition. More recently, a range of stoichiometries has been suggested in the literature which is represented by the formula La2CoO4+x. The variations in stoichiometry have previously been explained by the presence of excess oxygen or by inter‐growths of Ruddlesden‐Popper‐type phases, (AO(ABO3)n). In this work, X‐ray diffraction data confirmed the previous variations in lattice parameters but indicated that the material is lanthanum deficient, not rich in oxygen. Thermogravimetric analysis confirmed the existence of variable oxygen stoichiometry. These data were consistent with a range of compositions described by the general formula La1.83CoO4‐x, where 0 ≤x≤ 0.13. These materials contain a maximum of 50% trivalent cobalt when x= 0. In addition, thermo‐gravimetric experiments in lower partial pressures of oxygen have enabled us to isolate a new, fully reduced form, La1.83CoO3.75, which contains only divalent cobalt. A two‐ phase region exists between La1.83CoO3.75 and La1.83CoO3.87.
Gelation of Aluminum Hydroxide Sols
Authors: PIERRE ALAIN C. , UHLMANN DONALD R.
Published: March 2005

The gelation of aluminum hydroxide sols obtained from aluminum sec‐butoxide has been studied as a function of the conditions of preparation, including pH, temperature, and time of aging. The preceding studies of Yoldas have been extended in more acidic conditions, up to a molar proportion of 1.12 HNO3 per Al(OC4H9)3. It has been found that stable sols can easily be obtained by processing at any temperature between 20° and 90°C beyond a molar proportion of 0.28 HNO3. The corresponding gels are suggested to have a boehmite‐like structure in which there is a metastable folding of the (020) layers at 20°C, and a stable unfolding at 80°C, the two structures coexisting at intermediate processing temperatures.
Liquid‐Phase Sintering of Ceramics
Authors: MARION J. E. , HSUEH C. H. , EVANS A. G.
Published: March 2005

Expressions for the sintering rate in liquid‐phase sintering are derived for coupled‐interface dissolution and liquid‐phase diffusion. The analysis reveals the important role of stress gradients in the grain boundary phase and also shows that such gradients cannot be supplied by liquid‐phase flow. Stress‐supporting structure in the grain boundary phase is thus implied. The probable existence of such structure is revealed by diffuse dark‐field scattering studies, using transmission electron microscopy, on partially sintered alumina/anorthite bodies.
High‐Pressure Phase Transitions in Zirconia and Yttria‐Doped Zirconia
Authors: ALZYAB B. , PERRY C. H. , INGEL R. P.
Published: March 2005

Raman spectroscopy has been utilized to characterize the phase transformations and transition pressures in pure and doped zirconia containing 3, 4, and 5 wt% Y2O3. The pressure‐induced transformations were investigated to over 6 GPa (at room temperature) using a diamond anvil pressure cell. Pure zirconia single‐crystal samples transformed to a “new” tetragonal phase (different from the one obtained at high temperatures at atmospheric pressure) at about 4 GPa. The pressure transformation, like the temperature transition, was reversible and exhibited an approximately 0.45‐GPa hysteresis at room temperature. The 3 and 4 wt% Y2O3 crystals underwent a monoclinic (P21/b) to tetragonal (P42 nmc) phase transition similar to that observed at high temperatures. This phase change was found to be irreversible on releasing the pressure. The 5 wt% Y2O3 at atmospheric pressure consists of a tetragonal modification in a disordered cubic matrix; a gradual, but reversible, disordering transformation of the tetragonal precipitate takes place with pressure.
Melting Temperatures of Monazite and Xenotime
Authors: Hikichi Yasuo , Nomura Tsuyoshi
Published: March 2005

The melting temperatures of natural and synthetic monazite and xenotime (rare‐earth ortnophosphates) were measured, using a heliostat‐type solar furnace. The results obtained are as follows: natural monazite from Japan (2057°40°C), synthetic monazite RPO4 (R=La, 2072°20°C; R=Ce, 2045°20°C; R=Pr, 1938°20°C; R=Nd, 1975°20°C; R=Sm, 1916°20°C), and synthetic xenotime RPO4(R=Y, 1995°20°C; R=Er, 1896°20°C).
Acoustic Characterization of Poling Effects in PZT Ceramics
Authors: Jen Cheng‐Kuei , Chung Chul‐Jong , Shapiro Galina , Monchalin Jean‐Pierre , LANGLOIS PIERRE , Bussiere Jean F.
Published: March 2005

Acoustic velocity and attenuation were measured in poled and unpoled lead zirconate titanate (PZT) ceramics prepared by sintering and hot‐pressing under‐different conditions. Hot‐pressed PZT was found to have attenuation values approximately 1 order of magnitude smaller than simered PZT. For both materials, poling caused a decrease in attenuation. Depolarization and phase transition phenomena were also observed at elevated temperatures using a novel laser‐ultrasound technique in combination with conventional pulse‐echo measurements.
Glass Properties in the Yttria‐Alumina‐Silica System
Authors: Hyatt M. J. , Day D. E.
Published: March 2005

The glass formation region in the yttria‐alumina‐silica system was investigated. Properties of glasses containing 25 to 55 wt% yttria were measured and the effect of the composition was determined. The density, refractive index, thermal‐expansion coefficient, and microhardness increased with increasing yttria content. The dissolution rate in IN HCl increased with increasing yttria content and temperature. These glasses were also found to have high electrical resistivity.
Photosensitive Mechanism of Dopant‐Free, Ultraviolet‐Sensitive Calcium Aluminate Glasses
Authors: HOSONO HIDEO , YAMAZAKI KOJI , ABE YOSHIHIRO
Published: March 2005

Calcium aluminate glasses show high sensitivity to ultraviolet radiation without the doping of optically active components. A mechanism is proposed to account for their photosensitivity on the basis of the result that the cause of UV‐induced coloring is the emergence of two kinds of paramagnetic centers, an aluminum‐oxygen hole center (Al‐OHC) and an ozonide (O‐3). In this model, a peroxy linkage connecting tetrahedrally coordinated Al3+s and a physically dissolved O2 molecule are assumed to be present in the glasses as structural defects. On exposure to UV rays, the peroxy linkage homolvtically dissociates into a pair of A1‐OHC's by absorbing UV quanta and one of the two resulting A1‐OHC's combines with a nearby O2 to form an ozonide. Experimental evidences substantiating the mechanism are also reported.
Ion Exchange in Alkali Layers of Potassium β ‐Ferrite ((1 + x)K2O · 11Fe2O3) Single Crystals
Authors: ITO SHIGERU , KUBO NOBUO , NARIKI SHINYA , YONEDA NOBORU
Published: March 2005

The potassium ions in potassium β‐ferrite ((1 + x)K2O ·11Fe2O3) crystals were exchanged with Na+, Rb+, Cs+, Ag+, NH4+, and H3O+ in molten nitrates or in concentrated H2SO4. On the other hand, spinel and hexagonal ferrites were formed by soaking the crystals in the melt of divalent salts. The crystals of K+, Rb+, and Cs+β‐ferrites decomposed to form α‐Fe2O3 at high temperatures of 800° to 1100°C. In addition, H3O+, NH4+, and Ag+β‐ferrites decomposed to form α‐Fe2O3 at relatively low temperatures of 350° to 650°C, in accordance with the stabilities of the inserted ions. The electrical properties of some β‐ferrites were measured.
Some Roles of MgO and TiO2 in Densification of a Sinterable Alumina
Authors: IKEGAMI TAKAYASU , KOTANI KAZUO , Eguchi Katsuya
Published: March 2005

Sinterability of undoped, MgO‐doped, and TiO2‐doped Al2O3 has been examined by applying reported sintering equations. The order of sinterability was MgO‐doped ∼ undoped≪ TiO2‐doped Al2O3 in the initial and intermediate stages of sintering, but a relative sintered density at 1600°C for 1 h occurred in the order undoped < TiO2‐doped < MgO‐doped AI2O3. The dispersion of thermal grooving angles increased in the order MgO‐doped < undoped < TiO2‐doped Al2O3, The change of sinterability by the dopants is explained in terms of mobility of mass transfer estimated from a densification rate in the initial‐ and intermediate‐stage sintering and of dispersed driving forces of densification and grain growth qualitatively evaluated from the width of the dispersion of thermal grooving angles.
Enhanced Ionic Conduction in AgCl‐Al2O3 Composites Induced by Plastic Deformation
Authors: DUDNEY NANCY J.
Published: March 2005

Composites of AgCl and A12O3 were prepared by impregnating an alumina fiber paper with molten AgCl. The as‐prepared composites showed no enhancement in the conductivity compared with pure AgCl samples prepared in a similar manner. When plastically deformed, the conductivity of both the pure and composite materials increased. After annealing at high temperatures, the conductivity of the pure AgCl sample decreased to the as‐prepared value, whereas the composite maintained a 2‐ to 5‐fold enhanced conductivity. This enhanced conductivity is due to deformation‐induced defects which are stabilized by the alumina fibers rather than due to the AgCl/AI2O3 interface.
Effect of Joint Thickness and Residual Stresses on the Properties of Ceramic Adhesive Joints: I, Finite Element Analysis of Stresses in Joints
Authors: KIRCHNER HENRY P. , CONWAY JOSEPH C. , SEGALL A. E.
Published: March 2005

The finite element method was used to determine the stress distributions in adhesive joints prepared using alumina adher‐ends and silicate glass adhesives with varying thicknesses and thermal expansion coefficients. These analyses, together with the results of literature analyses for joints subjected to externally applied loads, aided in interpreting the experimental observations which are described in Part II of the paper.
Structural Transformations in the Decomposition of Mg(OH)2 and MgCO3
Authors: KIM M. G. , DAHMEN U. , SEARCY ALAN W.
Published: March 2005

A transmission electron microscopy study has been carried out to understand the structural transformation mechanisms of decomposition of Mg(OH)2 and MgCO3 under vacuum. Both Mg(OH)2 and MgCO3 decompose topotactically to yield porous pseudomorphic MgO of normal structure with definite orientation relationships. The decomposition of Mg(OH)2 yields MgO with a single orientation relationship, but that of MgCO3 leads to one major and two minor orientation relationships with two, six, and three variants, respectively. The major orientation relationships in the formation of 2‐ to 3‐nm cubic MgO particles are discussed in terms of a correlation between oxygen octahedra in the reactant solids. The small cubic MgO particles may aggregate spontaneously to reduce the excess surface energy and result in minute cracks.
Strengthening of Oxide Ceramics by Transformation‐Induced Stress
Authors: VIRKAR ANIL V. , HUANG JOW LAY , CUTLER RAYMOND A.
Published: March 2005

Alumina‐zirconia composites were fabricated by isostatic pressing and sintering of powder mixtures in such a way that bar‐shaped specimens consisted of three layers. The outer layers contained A12O3 and unstabilized ZrO2 while the central layer contained A12O3 and partially stabilized ZrO2 (with 2 mol% Y2O3). When cooled from the sintering temperature, some of the zirconia in the outer layers transformed to the monoclinic form while zirconia in the central layer was retained in the tetragonal form. The transformation of zirconia in the outer layers led to the establishment of surface compressive stresses and balancing tensile stresses in the bulk. The existence of surface compressive stresses was verified by a strain gauge technique and bending strength measurements on samples with varying thickness of the outer layers. The layered composites exhibited greater strength in comparison with monolithic Al2O3‐ZrO2 specimens. Further, variation of strength in bending with outer layer thickness (for a fixed total thickness) indicated that failure occurred from internal flaws. Scanning electron microscopy of fracture surfaces revealed that strength‐limiting flaws were voids located in the central layer near the interface separating the central and the outer layers.
Crystallization Behavior of Al2O3 in the Presence or SiO2
Authors: Chakravorty Akshoy Kumar , Ghosh Dilip Kumar
Published: March 2005

The independent crystallization sequence of an Al2O3 component is modified in the presence of SiO2 and vice versa. Mixed SiO2‐Al2O3, gel (28 wt% SiO2 and 72 wt% Al2O3) forms neither cristobalite nor γ‐Al2O3 and corundum at 1000°C but forms Si‐Al spinel; an amorphous aluminosilicate phase invariably also forms after the gel is heated. However, the composition of this amorphous aluminosilicate phase is not as yet known.
Effects of Antimony Oxide on the Characteristics of ZnO Varistors
Authors: TAKEMURA TAKETOSHI , KOBAYASHI MASAHIRO , TAKADA YOSHIO , SATO KEN
Published: March 2005

The breakdown voltage, the upturn voltage, and the nonlinearity of the ZnO varistors are significantly influenced by the Sb2O3 and SiO2 contents, as well as by the β→γ transition of the Bi2O3 phase. The lattice parameter of spinel is influenced by the coexisting Bi2O3 phase. Antimony oxide disperses into the powders of ZnO and other additives in the early stage of sintering, and finally gathers again as particles of spinel which may play an important role in the improvement of the nonlinearity by stressing the interfaces of two ZnO grains.
Chemical Durability of Some Sodium Borosilicate Glasses Improved by Phase Separation*
Authors: TAYLOR PETER , ASHMORE SHEILA D. , OWEN DERREK G.
Published: March 2005

Dissolution of glass coupons with the general composition χNa2O.(100–χ)[0.33B2O3·0.67SiO2], with χ varying from 3 to 11, has been monitored with and without prior phase separation of the glasses. A major reduction in dissolution rates was noted upon phase separation of glasses with χ≃ 3. This was correlated with the development of a phase‐separated microstructure in which the less durable, (Na2O + B2O3)‐rich phase was dispersed as discrete particles within a more durable, SiO2‐rich matrix. The degree of improvement in durability was strongly dependent on Na2O content, and was marginal with χ≃ 5.
Effect of a Liquid Phase on the Morphology of Grain Growth in Alumina
Authors: KAYSSER WOLFGANG A. , SPRISSLER MARIANNE , HANDWERKER CAROL A. , BLENDELL JOHN E.
Published: March 2005

In this investigation we have studied how the presence of a liquid phase affects the grain morphology and grain growth kinetics in Al2O3at 1800°C using the growth of both matrix grains and large spherical single‐crystal seeds growing into the matrix. The growth rates of the matrix grains were found to decrease in the following order: undoped Al2O3, AI2O3with anorthite, AI2O3with anorthite and MgO, and Al2O3with MgO. Except for the samples doped with MgO alone, the matrix grains were faceted and appeared tabular in polished sections. In samples containing anorthite both with and without MgO, the single‐crystal seeds exhibit basal facets with continuous liquid films and slow growth in the 〈0001〉 relative to all other crystallographic directions. When only MgO is added, the growth of the single‐crystal seeds was not isotropic; however, no faceting was observed. We discuss how anisotropic growth rates caused by the anorthite additions can stimulate discontinuous grain growth in Al2O3.
Strength, Structure, and Fracture Properties of Ceramic Fibers Produced from Polymeric Precursors: I, Base‐Line Studies
Authors: SAWYER LINDA C. , JAMIESON MARJORIE , BRIKOWSKI DUANE , HAIDER M. ISHAQ , CHEN RONG T.
Published: March 2005

Classical brittle failure has been observed for ceramic fibers produced by pyrolysis from three different polymer precursors. Characterization by SEM fractography methods has shown typical flaw‐mirror‐mist‐hackle morphology and such study has provided observations for understanding the fracture mechanisms. The gage length dependence of tensile strength combined with the fractography study showed the flaw‐controlled failure mechanism of all the ceramic fibers. Systematic failure types have been identified for specific strength ranges. Complementary study of the microstructure and chemical structure by TEM, X‐ray diffraction, and electron spectroscopy for chemical analysis (ESCA) has shown the nature of the bulk ceramic to be predominantly random and glassy even in the case of a fiber with microcrystalline β‐SiC. Fracture mechanics calculations have shown the fibers all behave as glasses.
Simple Processing Method for High‐Strength Silicon Carbide
Authors: Hurst Janet B. , Dutta Sunil
Published: March 2005

Silicon carbide test bars were made by a simple wet‐processing technique. The pressure casting method used the same equipment as conventional dry‐pressing, but with a modified die. This casting technique was employed in order to produce test bars with improved strength and smaller fracture flaws than produced by dry‐pressing. This was accomplished by eliminating pore clusters which were present in dry‐pressed specimens and identified as a common source of failure in SiC MOR test bars.
Iron‐Excess Manganese Ferrite: Electrical Conductivity and Cation Distributions
Authors: YOO HAN‐ILL , TULLER HARRY L.
Published: March 2005

The electronic conductivity and thermoelectric power of a magnetic ferrite of composition Mn0.863Fe2.137O4 have been measured as functions of oxygen partial pressure and temperature. Within the single‐phase region of the spinel ferrite, both electrical properties are essentially independent of the oxygen partial pressure, implying that the electronic charge carrier concentration is governed by the molecularity rather than by oxygen nonstoichiometry. The electrical conduction behavior is successfully interpreted on the basis of a small polaron model, yielding a hopping energy of 0.363 ± 0.008 eV and a drift mobility of 0.05 to 0.10 cm2/(V·s) in the temperature range of 900 to 1300 K.
Effect of Grain‐Boundary Oxidation on Fracture Toughness of SiC
Authors: ZDANIEWSKI WIESLAW A. , KIRCHNER HENRY P.
Published: March 2005

Hot‐pressed SiC was oxidized at temperatures from 900° to 1300°C, and the fracture toughness was determined by the indentation method. The apparent fracture toughness of the surface layers increased with oxidation temperature and then decreased. The observed variations in apparent fracture toughness were consistent with earlier observations of strength variations in oxidized SiC. Some specimens were fractured, and the fracture surfaces were characterized. Based on these observations, the variations in fracture toughness were attributed to variations in residual compressive stresses induced by oxidation.
Surface Characterization of Zirconia After Reaction with Water
Authors: Kagawa Masahiro , Omori Mamoru , Syono Yasuihiko , Imamura Yoko , Usui Shinnosuke
Published: March 2005

Ultrafine ZrO2, Y2O3, and TZP (ZrO2+‐3 mol% Y2O3) powders were reacted with water under various conditions; hydration of their particle surfaces was investigated by measuring electrophoretic mobilities. The mobilities were independent of pH after the reaction at 250° to 300°C for 240 h, indicating that the surface is not hydrated. Refluxing of the powders in water for 170 h brought about a pH dependence of mobility, indicating hydration of the surface.