bluuebunny/crossref_metadata_2025 huggingface dataset:
novoSNP, a novel computational tool for sequence variation discovery
Authors: Weckx Stefan , Del-Favero Jurgen , Rademakers Rosa , Claes Lieve , Cruts Marc , De Jonghe Peter , Van Broeckhoven Christine , De Rijk Peter
Published: March 2005

Technological improvements shifted sequencing from low-throughput, work-intensive, gel-based systems to high-throughput capillary systems. This resulted in a broad use of genomic resequencing to identify sequence variations in genes and regulatory, as well as extended genomic regions. We describe a software package, novoSNP, that conscientiously discovers single nucleotide polymorphisms (SNPs) and insertion-deletion polymorphisms (INDELs) in sequence trace files in a fast, reliable, and user-friendly way. We compared the performance of novoSNP with that of PolyPhred and PolyBayes on two data sets. The first data set comprised 1028 sequence trace files obtained from diagnostic mutation analyses of SCN1A (neuronal voltage-gated sodium channel α-subunit type I gene). The second data set comprised 9062 sequence trace files from a genomic resequencing project aiming at the construction of a high-density SNP map of MAPT (microtubule-associated protein tau gene). Visual inspection of these data sets had identified 38 sequence variations for SCN1A and 488 for MAPT. novoSNP automatically identified all 38 SCN1A variations including five INDELs, while for MAPT only 15 of the 488 variations were not correctly marked. PolyPhred detected far fewer SNPs as compared to novoSNP and missed nearly all INDELs. PolyBayes, designed for the sequence analysis of cloned templates, detected only a limited number of the variations present in the data set. Besides the significant improvement in the automated detection of sequence variations both in diagnostic mutation analyses and in SNP discovery projects, novoSNP also offers a user-friendly interface for inspecting possible genetic variations.
Computational analysis of 3′-ends of ESTs shows four classes of alternative polyadenylation in human, mouse, and rat
Authors: Yan Jun , Marr Thomas G.
Published: March 2005

Alternative initiation, splicing, and polyadenylation are key mechanisms used by many organisms to generate diversity among mature mRNA transcripts originating from the same transcription unit. While previous computational analyses of alternative polyadenylation have focused on polyadenylation activities within or downstream of the normal 3′-terminal exons, we present the results of the first genome-wide analysis of patterns of alternative polyadenylation in the human, mouse, and rat genomes occurring over the entire transcribed regions of mRNAs using 3′-ESTs with poly(A) tails aligned to genomic sequences. Four distinct classes of patterns of alternative polyadenylation result from this analysis: tandem poly(A) sites, composite exons, hidden exons, and truncated exons. We estimate that at least 49% (human), 31% (mouse), and 28% (rat) of polyadenylated transcription units have alternative polyadenylation. A portion of these alternative polyadenylation events result in new protein isoforms.
Post-entrapment genome engineering: First exon size does not affect the expression of fusion transcripts generated by gene entrapment
Authors: Osipovich Anna B. , Singh Aparna , Ruley H. Earl
Published: March 2005

Gene trap mutagenesis in mouse embryonic stem cells has been widely used for genome-wide studies of mammalian gene function. However, while large numbers of genes can be disrupted, individual mutations may suffer from limitations due to the structure and/or placement of targeting vector. To extend the utility of gene trap mutagenesis, replaceable 3′ [or poly(A)] gene trap vectors were developed that permit sequences inserted in individual entrapment clones to be engineered by Cre-mediated recombination. 3′ traps incorporating different drug resistance genes could be readily exchanged, simply by selecting for the drug-resistance gene of the replacement vector. By substituting different 3′ traps, we show that otherwise identical fusion genes containing a large first exon (804 nt) are not expressed at appreciably lower levels than genes expressing small first exons (384 and 151 nt). Thus, size appears to have less effect on the expression and processing of first exons than has been reported for internal exons. Finally, a retroviral poly(A) trap (consisting of a RNA polymerase II promoter, a neomycin-resistance gene, and 5′-splice site) typically produced mutagenized clones in which vector sequences spliced to the 3′-terminal exons of cellular transcription units, suggesting strong selection for fusion transcripts that evade nonsense-mediated decay. The efficient exchange of poly(A) traps should greatly extend the utility of mutant libraries generated by gene entrapment and provides new strategies to study the rules that govern the expression of exons inserted throughout the genome.
Idle Rights: Employees' Rights Consciousness and the Construction of Sexual Harassment Policies
Authors: Marshall Anna-Maria
Published: March 2005

This article analyzes women's legal consciousness in responding to unwanted sexual attention in the workplace. By focusing on a particular social problem, this study is situated in the particular legal domain of sexual harassment laws and in a specific organizational context. Taking the perspective of the intended beneficiaries of sexual harassment policies and procedures—women with complaints about sexual conduct in the workplace—I show that the implementation of grievance procedures creates powerful obstacles to women's efforts to assert those rights. Moreover, the practices implementing the policies can alter the very definition of sexual harassment in that setting. Thus, in enacting grievance procedures, women and supervisors construct a legality in particular workplaces that offers only limited protection for women's rights.
Transportation versus Imprisonment in Eighteenth- and Nineteenth-Century Britain: Penal Power, Liberty, and the State
Authors: Willis James J.
Published: March 2005

Existing explanations for historical changes in punishment in Britain have tended to examine the replacement of disorderly prisons and public executions with national penitentiaries from the late eighteenth to the mid-nineteenth century. Despite their significant contributions to our understanding of how punishments operate in a broader social, political, and economic context, these scholarly accounts have narrowed debate on the mechanisms of penal change to the intentions of penal reformers. This analysis extends this time frame and uses historical data to compare the development of the penitentiary in Britain to its primary, yet less studied, penal substitute, the transportation of felons to America and Australia. In doing so, it provides an alternative explanation for the ascendancy of national penitentiaries. I argue that the development of these penal institutions in Britain was historically made possible by two interdependent sets of changes: (1) changes in the structure and administration of the state's penal apparatus (from decentralized to centralized and patrimonial to bureaucratic); and (2) transformations in popular understandings of the state's power to punish in correspondence with the expansion of a broader and more equal definition of citizenship (democratization). In conclusion, I argue for the value of perspectives on punishment that identify the explicit relationships between state organization and social relations in order to clarify how culture inheres in material conditions to influence specific penal outcomes.
Stepping Into the Fray: When Do Mediators Mediate?
Authors: Greig J. Michael
Published: March 2005

In this article, I analyze the conditions that promote the request, offer, and occurrence of mediation between enduring rivals. Although the mediation literature has devoted considerable attention to the form that mediation takes, the approaches that mediators use, and the conditions under which it is successful, little attention has been given to the conditions under which mediation is most likely to occur. The results of the analysis point to a disconnect among enduring rivalries between the factors that the literature highlights as promoting mediation success and those that promote the onset of mediation. This disconnect is particularly apparent in the conditions that prompt third‐parties to offer mediation.
The Development of Stable Party Support: Electoral Dynamics in Post‐Communist Europe
Authors: Tavits Margit
Published: March 2005

What conditions help stable patterns of party support to emerge? Using pooled time‐series cross‐section data on election results from 15 East European democracies, the empirical analysis finds that (1) right after a regime change electoral volatility increases while the trend is reversed after democracy has endured for about a decade; (2) ethnic cleavages have no effect on stability while social cleavages affect electoral stability only during economic downturns; (3) both institutions and economic performance influence the stability of party support; however, the effect of the latter diminishes over time when democracies mature.
Issues and Institutions: “Winnowing” in the U.S. Congress
Authors: Krutz Glen S.
Published: March 2005

“Winnowing” is the pre‐floor process by which Congress determines the small percentage of bills that will receive committee attention. The vast majority of proposals languish in this vital agenda‐setting stage, yet our understanding of winnowing is nascent. Why do some bills move forward while most fail? I examine that question here by developing and testing a theoretical framework of winnowing grounded in bounded rationality, which includes institutional and sponsor cues and also incorporates the unique issue milieu. A heteroskedastic probit model is utilized to analyze the winnowing fate of all bills introduced across five issue areas in the House and Senate from 1991 to 1998. The findings counter much received wisdom and suggest that the process is indeed cue based. The majority party helps structure this critical process in both chambers, though party effects appear stronger in the House. Contrary to recent work on the rise of Senate individualism, the seniority of the sponsor has significant effects in both the Senate and House, but again exhibits a stronger effect in the House. Surprisingly, presidential proposals are no more likely to survive than typical bills. The findings further suggest that the entrepreneurial efforts of bill sponsors breathe life into this process.
Democracy and Education Spending in Africa
Authors: Stasavage David
Published: March 2005

While it is widely believed that electoral competition influences public spending decisions, there has been relatively little effort to examine how recent democratization in the developing world has resulted in changes in basic service provision. There have been even fewer attempts to investigate whether democracy matters for public spending in the poorest developing countries, where “weak institutions” may mean that the formal adoption of electoral competition has little effect on policy. In this article I confront these questions directly, asking whether the shift to multiparty competition in African countries has resulted in increased spending on primary education. I develop an argument, illustrated with a game‐theoretic model, which suggests that the need to obtain an electoral majority may have prompted African governments to spend more on education and to prioritize primary schools over universities within the education budget. I test three propositions from the model using panel data on electoral competition and education spending in African countries. I find clear evidence that democratically elected African governments have spent more on primary education, while spending on universities appears unaffected by democratization.
Striking a Responsive Chord: How Political Ads Motivate and Persuade Voters by Appealing to Emotions
Authors: Brader Ted
Published: March 2005

Politicians routinely appeal to the emotions of voters, a practice critics claim subverts the rational decision making on which democratic processes properly rest. But we know little about how emotional appeals actually influence voting behavior. This study demonstrates, for the first time, that political ads can change the way citizens get involved and make choices simply by using images and music to evoke emotions. Prior research suggests voters behave differently in different emotional states but has not established whether politicians can use campaigns to manipulate emotions and thereby cause changes in political behavior. This article uses two experiments conducted during an actual election to show that: (1) cueing enthusiasm motivates participation and activates existing loyalties; and (2) cueing fear stimulates vigilance, increases reliance on contemporary evaluations, and facilitates persuasion. These results suggest campaigns achieve their goals in part by appealing to emotions, and emotional appeals can promote democratically desirable behavior.
Talking the Vote: Why Presidential Candidates Hit the Talk Show Circuit
Authors: Baum Matthew A.
Published: March 2005

The 2000 presidential election found the major party presidential candidates chatting with Oprah Winfrey, Rosie O'Donnell, and Regis Philbin, trading one‐liners with Jay Leno and David Letterman, and discussing rap music on MTV. This study investigates the impact of entertainment‐oriented talk show interviews of presidential candidates, using the 2000 election as a case study. I consider why such shows cover presidential politics, why candidates choose to appear on them, and who is likely to be watching. This discussion yields a series of hypotheses concerning the effects of these interviews on public attitudes and voting behavior. I test my hypotheses through a content analysis of campaign coverage by entertainment‐oriented talk shows, traditional political interview shows, and national news campaign coverage, as well as through a series of statistical investigations. I find that politically unengaged voters who watch entertainment‐oriented TV talk shows are more likely to find the opposition party candidate likeable, as well as to cross party lines and vote for him, relative to their counterparts who are more politically aware or who do not watch such shows.
Bactericidal activity of flucloxacillin against Staphylococcus aureus in primary keratinocyte cultures of lesional and unaffected skin of patients suffering from atopic dermatitis
Authors: Vollmert C. , Behrendt H.
Published: March 2005

Abstract:  More than 90% of patients with atopic dermatitis (AD) are colonized by Staphylococcus aureus. Due to prevalent multi‐resistant strains, it is highly difficult to eliminate S. aureus contamination of primary cell cultures of human AD skin by means of the antibiotics commonly used in cell culture. Therefore, an anti‐staphylococcal treatment was investigated by which sterile proliferating keratinocyte cultures are attained from lesional and unaffected skin of AD patients by applying flucloxacillin, which in general is systemically used in vivo. The treatment with 1% flucloxacillin for 20 min included both colonized skin samples and contaminated primary cell cultures. In the case of persistent contamination, this step was repeated as often as required until complete decontamination without any cytotoxic indications was achieved. Antibacterial treatment with flucloxacillin permitted the cultivation of sterile, vital, and proliferating primary cultures of human skin keratinocytes from lesional and unaffected skin of AD patients with S. aureus colonization. The method increased the success rate of isolation of AD keratinocytes from 30 to 90%, representing on average 3 vs. 9 successfully isolated, sterile and proliferating cultures out of 10 contaminated skin biopsies, which is comparable to normal human keratinocyte isolation rates.
Polyunsaturated fatty acids partially reproduce the role of melanocytes in the epidermal melanin unit
Authors: Cario‐André Muriel , Briganti Stefania , Picardo Mauro , Nikaido Osamu , De Verneuil Hubert , Taïeb Alain
Published: March 2005

Abstract:  The incidence rate of melanoma is higher in fair‐skinned than in dark‐skinned individuals. In negroid skin there is more eumelanin which is present in all skin layers and fewer polyunsaturated fatty acids (PUFA) than in caucasoid skin. The western diet, which is rich in omega–6 polyunsaturated fatty acids, is associated with more proneness to cancer including cutaneous melanoma. To study the respective influence of omega‐6 PUFA and low phototype melanocytes on redox status ‐basal and following UV irradiation‐, we used epidermal reconstructs. The addition of polyunsaturated fatty acids as well as the presence of low phototype melanocytes affected basal status similarly except for catalase activity, which decreased significantly in polyunsaturated fatty acid‐supplemented reconstructs. Following UV, polyunsaturated fatty acids and low phototype melanocytes increased lipid and protein oxidative damage without affecting direct DNA damage. However, polyunsaturated fatty acids increased epidermal apoptosis whereas low phototype melanocytes decreased it. Since our data suggest that an omega‐6 PUFA rich‐diet may increase oxidative damage in melanocytes without inducing apoptosis, the long‐term net outcome could be cumulated mutations and an increased risk of skin cancer, especially melanoma.
FGF‐2 blocks TGF‐β1‐mediated suppression of Bcl‐2 in normal melanocytes
Authors: Von Willebrand Maria , Köhler Klaus , Alanko Tuomo , Laiho Marikki , Saksela Olli
Published: March 2005

Abstract:  Normal melanocytes require growth support provided by the adjacent basement membrane. In contrast, nevus cells and melanoma cells survive in the dermis, and in vitro on a soft collagen gel. Transforming growth factor‐β1 (TGF‐β1) produced by melanocytes themselves induces apoptosis in normal melanocytes cultured on collagen gel, an effect that can be counteracted by fibroblast growth factor‐2 (FGF‐2). The purpose of this study was to investigate the mechanisms by which FGF‐2 counteracts the apoptotic signals from TGF‐β1 in melanocytes cultured on collagen gel. We report that FGF‐2 did not interfere with the signal transduction from the TGF‐β1 receptors to SMAD2/3 proteins. Instead, TGF‐β1 decreased the level of Bcl‐2 in normal melanocytes cultured on collagen gel, and FGF‐2 reversed the TGF‐β1‐mediated reduction in the level of Bcl‐2. In nevus and melanoma cells, TGF‐β1 was unable to induce a decrease in the level of Bcl‐2, and treatment with FGF‐2 did not cause an increase in the level of Bcl‐2 in nevus or melanoma cells. In conclusion, our results suggest that a reduction in the level of the anti‐apoptotic Bcl‐2 is involved in the execution of apoptosis induced by TGF‐β1 in normal melanocytes cultured on collagen gel and that FGF‐2 can prevent TGF‐β1 from causing this reduction.
Glass Formation Range, Acid Resistivity, and Surface Charge Density of ZnO‐B2O3‐SiO2 Passivation Glass Containing Al2O3
Authors: SHIMBO MASARU , TAI SHINICHI , TANZAWA KATSUJIRO
Published: March 2005

The glass formation range in the system ZnO‐B2O3‐SiO2 increases when 5% Al2O3 is added and then decreases with further Al2O3 additions. The acid resistivity of the glass also increases when Al2O3 is added. An observed increase in negative charge with Al content until the system contains equal amounts of Al and Si (in forms of mole %) is explained by the formation of AlO4− tetrahedra which substitute in the SiO4 network. Alkaline‐earth oxides cause a positive charge which compensates for the negative charge formed by Al2O3. Antimony oxide and lanthanum oxide result in a negative charge in the glass. The formation of a negative or positive charge in the glass is thought to reflect the acidity or basicity of the glass, respectively.
Solubility and Transport of NiO Cathodes in Molten Carbonate Fuel Cells
Authors: BAUMGARTNER CHARLES E.
Published: March 2005

Equilibrium NiO solubility measurements were made in Li2CO3/K2CO3 mixtures as a function of temperature, ambient gas environment, and salt composition for gases containing 3.1% H2O. The equilibrium solubility was found to increase with increasing temperature, CO2 partial pressure, and cation fraction Li+ and to decrease slightly with increasing O2 partial pressure. These results were coupled with theoretical predictions of (1) O2, H2, and CO2 activities and (2) compositional gradients which develop across the electrolyte structure of an operating carbonate fuel to explain the two distinct regions of nickel precipitation across the fuel cell. Precipitation occurs near the cathode because NiO solubility decreases commensurate with electrolyte compositional gradients, whereas the second region deeper within the electrolyte matrix results from a decreased O2 activity.
Implications of Transformation Plasticity in ZrO2‐Containing Ceramics: II, Elastic‐Plastic Indentation
Authors: CHEN I‐WEI
Published: March 2005

Indentation hardness of partially stabilized zirconia was found to be 8.2 times the uniaxial compressive yield stress. This ratio is anomalously high for ceramic materials and is attributed to pressure hardening in transformation plasticity. An analytic solution of elastic‐plastic indentation using the spherical‐hole model is given, based on a pressure‐sensitive idealized yield criterion. The theory correctly predicts a higher hardness and a larger plastic zone, both in quantitative agreement with the experimental observations in Mg‐PSZ. Data analysis further reveals a large disparity of yield stress and hardness values among cubic, tetragonal, and monoclinic zirconias, resulting from their different phase transformation and twinning capabilities. The broader implications of pressure sensitivity in elastic‐plastic Indentation are rationalized.
Influence of an Amorphous Second Phase on the Properties of Yttria‐Stabilized Tetragonal Zirconia Polycrystals (Y‐TZP)
Authors: MECARTNEY M.L.
Published: March 2005

Y‐TZP ceramics with various amounts of glassy intergranular phase were fabricated in order to investigate the effect of this amorphous phase on the properties of TZP. The presence of a liquid silicate phase not only enhanced sintering but also controlled the evolution of distinctly different grain morphologies, dependent on the amount of liquid phase present. The influence of the glass phase on the transformability of grains is discussed with respect to the room‐temperature fracture toughness and surface degradation at 250°C.
Defect Chemistry of BaTiO3 with Additions of CaTiO3
Authors: ZHANG XIAO WEN , HAN YOUNG HO , LAL MISRI , SMYTH DONALD M.
Published: March 2005

The substitution of up to 5% Ca2+ for Ba2+ in BaTiO3 results in a shift in the oxygen pressure dependence of the equilibrium electrical conductivity that is in the same direction as that caused by addition of acceptor impurities such as Al3+ or Ca2+ substituted for Ti4+. In contrast to the latter effect, however, the shape of the conductivity plot is not changed, the conductivity value at the conductivity minimum is not affected, and the amount of the shift increases with decreasing temperature of measurement. It is shown that the shift is primarily due to an increase in the enthalpy of reduction and a decrease in the enthalpy of oxidation as increasing amounts of Ba2+ are replaced by Ca2+.
Formation and Transformation of WO3 Prepared from Alkoxide
Authors: Yamaguchi Osamu , Tomihisa Daijo , Kawabata Hidenao , Shimizu Klyoshi
Published: March 2005

Amorphous WO3 or WO3 or H2O is formed by hydrolysis of tungsten ethoxide. The temperature of hydrolysis influences the crystallization of WO3·H2O. Tungsten hydrate (WO3·H2O) has an orthorhombic unit cell with a=0.5235 nm, b = 1.0688 nm, and c=0.5123 nm. Orthorhombic WO3 crystallizes at 350° to 500°Cfrom amorphous WO3. Cubic WO3 is formed at 200° to 310°C with dehydration of WO3·H2O. WO3 transformations are examined by high‐temperature X‐ray diffraction. The kinetics of formation of the cubic modification have been studied by measuring the weight decrease with a thermobalcnce. Formation isotherms can be interpreted in terms of the first‐order equation –In (1–f)=kt; activation energies are 110 and 80 kJ mol−1 for initial and final stages, respectively.
Packing and Sintering of Two‐Dimensional Structures Made fro Bimodal Particle Size Distributions
Authors: LINIGER ERIC , RAJ RISHI
Published: March 2005

Binary mixtures of spheres were used to prepare a variety of two‐dimensional structures ranging from ordered to disordered. The extent of particle order was influenced by the size ratio and the concentration of the bimodal constituents. If either the sizes or the concentrations were very different, the structures became phase separated into ordered regions of small spheres and ordered regions of large spheres. Disordered structures were produced when particles were present in equal concentrations and when sizes differed by about 30%. The sintering behavior of these two‐dimensional structures was also examined. The domain boundaries in the ordered samples were found to develop into cracks during sintering if the domain size was large. In contrast the disordered structures sintered homogeneously, without the formation of large processing defects.
Strength Variability of Indented Soda‐Lime Glass
Authors: GLAESEMANN G. SCOTT , JAKUS KARL , RITTER JOHN E.
Published: March 2005

Studies of annealed indentation flaws show that specimen strength is inversely proportional to the square root of the surface trace dimension of the strength‐controlling radial crack over a range of indentation loads. Using the surface trace as the characteristic dimension in the appropriate fracture mechanics equations, however, underestimates the measured strengths by about 30%. There is also a lack of correlation between the individual strengths and the surface traces at a given indentation load. Despite the complex nature of indentation flaws, strength predictions of individual indentation cracks based on the radial crack depth (not the surface trace) are in agreement with measured strengths. Strength variability of indented glass specimens at a given indentation load is due mainly to the spectrum of crack depths.
Compositional Model for Calcium Silicate Hydrate (C‐S‐H) Gels, Their Solubilities, and Free Energies of Formation
Authors: GLASSER FREDRIK P. , LACHOWSKI ERIC E. , MACPHEE DONALD E.
Published: March 2005

A compositional model based on available structural evidence is proposed for amorphous calcium silicate hydrogel. It is applicable to gels in the (Ca/Si),solid range 1.0 to 1.4 and is formulated to take account of dimeric silicate species in the solid. Its composition is represented by CaxH6−2xSi2O7·zCa(OH)2·nH2O where x and z are not independently obtainable; x+z, however, is evaluated from the Ca/Si ratio. The model is applied to representative solubility data; Ksp and free energies of formation for C‐S‐H's in this composition range are evaluated.
Surface Chemistry and Structure of Ultrafine Silicon Carbide: An FT‐IR Study
Authors: Ramis Gianguido , Quintard Pierre , Cauchetier Michel , Busca Guido , Lorenzelli Vincenzo
Published: March 2005

Using transmission FT‐IR, surface characterizations are performed on ultrafine SiC powders produced by a laser‐driven method. The surface species sensitive to thermal treatments (OH, CHx,, C = O, SiHx) are identified on samples evacuated at various temperatures. Absorption bands attributed to overtones of the fundamental Si—C modes are also present in the IR spectra and remain unchanged after treatment. The reaction of SiC with oxygen and water vapor produces a layer of silica on the sample and gaseous CO2; the reaction with ammonia results in a partial nitridation of the surface, with the formation of NHx groups that apparently increase the stability of the SiC against oxidation; and reaction with hydrogen produces methane in the gas phase and causes the disappearance of the bands due to surface CHx groups.
Carbon‐13 and Oxygen‐18 Mass Spectrometry as a Potential Tool for the Study of Carbonate Phases in Concretes
Authors: Létolle René , Gégout Philippe , Moranville‐Regourd Micheline , Gaveau Bénédicte
Published: March 2005

The abundance of carbon‐13 and oxygen‐18 in cement carbonates shows important variations linked to the precipitation process. Three groups of values are observed: (1) the highest values (mean δ13 and δ18= 0 per mil versus PDB and + 30 per mil versus SMOW, PDB and SMOW being the international geochemical isotope standards) are specific of carbonate fillers made from marine sedimentary limestones; (2) the lowest values are linked to direct absorption of atmospheric CO2 by high‐pH cement solutions with important kinetic effects and no isotope equilibration in the high‐pH zone (δ13 and δ18 range from ‐35 per mil to ‐18 per mil versus PDB and +18 per mil to +8 per mil versus SMOW, respectively); and (3) the intermediate group (δ13 and δ18 range from +20 per mil to +30 per mil versus PDB and ‐10 per mil to ‐15 per mil versus SMOW, respectively) is due to precipitation of the mineral‐carbon system dissolved in water. Stable isotope measurements, therefore, may provide information on the proportion and chemical origin of various carbonate generations in concrete.
Mullite Formation Kinetics of a Single‐Phase Gel
Authors: Li Dong X. , Thomson William J
Published: March 2005

A reaction kinetic study of the formation of mullite from single‐phase aluminosilicate gels has been performed using dynamic X‐ray diffraction. In situ measurements of conversion and separate infrared spectra data indicate that the amorphous single‐phase precursors form crystalline mullite at temperatures as low as 1213 K. All of the data are consistent with a nucleation rate‐controlled mechanism, unlike previous work with diffusion‐limited powders and diphasic gels. At temperatures below 1400 K, the conversion data are adequately fit with a binary model that can approximate a uniform distribution of activation energies. At higher temperatures, evidence indicates that diffusion mechanisms become the rate‐limiting step.
Toughening of a Particulate‐Reinforced Ceramic‐Matrix Composite by Thermal Residual Stress
Authors: Taya Minoru , Hayashi S. , Kobayashi Albert S. , Yoon H. S.
Published: March 2005

The micromechanics involved in increased crack growth resistance, KR, due to the addition of TiB2 particulate in a SiC matrix was analyzed both experimentally and theoretically. The fractography evidence, in which, the advancing crack was attracted to adjacent particulates, was attributed to the tensile region surrounding a particulate. Countering this effect is the compressive thermal residual stress, which results in the toughening of the composite, in the matrix. This thermal residual stress field in a particulate‐reinforced ceramic‐matrix composite is induced by the mismatch in the coefficients of thermal expansion of the matrix and the particulate when the composite is cooled from the processing to room temperature. The increase in KR of the composite over the monolithic matrix, which was measured by using a hybrid experimental‐numerical analysis, was 77%, and compared well with the analytically predicted increase of 52%. The increase in KR predicted by the crack deflection model was 14%. Dependence of KR on the volume fraction of particulates, fp, and of voids, fv, is also discussed.
Modeling Localized Defects in Ionic Materials Using Mott‐Littleton and Embedded Quantum Cluster Methodology
Authors: Grimes Robin W. , Catlow C. Richard A.
Published: March 2005

Embedded quantum cluster and Mott‐Littleton techniques are used to study defects in MgO, UO2, and FeO. Through these calculations we illustrate the importance of lattice relaxation and provide evidence that the quantum cluster methodology is both compatible with and complementary to a Born‐like ionic model. We discuss the limitations of both methods. Within the Mott‐Littleton framework we consider the derivation of effective pair potentials, region sizes, and the application to complex systems. For embedded quantum cluster calculations we investigate basis sets and discuss effective embedding procedures.
Toughening of Silicon Nitride Matrix Composites by the Addition of Both Silicon Carbide Whiskers and Silicon Carbide Particles
Authors: Kodama Hironori , Suzuki Takaaki , Sakamoto Hiroshi , Miyoshi Tadahiko
Published: March 2005

Si3N4 matrix composites reinforced by SiC whiskers, SiC particles, or both were fabricated using the hot‐pressing technique. The mechanical properties of the composites containing various amounts of these SiC reinforcing materials and different sizes of SiC particles were investigated. Fracture toughness of the composites was significantly improved by introducing SiC whiskers and particles together, compared with that obtained by adding SiC whiskers or SiC particles alone. On increasing the size of the added SiC particles, the fracture toughness of the composites reinforced by both whiskers and particles was increased. Their fracture toughness also showed a strong dependence on the amount of SiC particles (average size 40 μm) and was a maximum at the particle content of 10 vol%. The maximum fracture toughness of these composites was 10.5 MPa·m1/2 and the flexural strength was 550 MPa after addition of 20 vol% of SiC whiskers and 10 vol% of SiC particles having an average particle size of 40 μm. These mechanical properties were almost constant from room temperature to temperatures around 1000°C. Fracture surface observations revealed that the reinforcing mechanisms acting in these composites were crack deflection and crack branching by SiC particles and pullout of SiC whiskers.
Structural Studies of Anomalous Behavior in the Silica‐Alumina Gel System
Authors: Hietala Susan L. , Smith Douglas M. , Brinker C. Jeffrey , Hurd Alan J. , Carim Altaf H. , Dando Neal
Published: March 2005

This paper compares the structure ofAl2O3‐SiO2 xerogels prepared with Al2O3 contents ranging from 21 to 75 wt% (13 to 64 mol%). The 47 wt% Al2O3 xerogel (Al/Si ≅ 1) exhibits anomalously low surface area (≅1 m2/g) and skeletal density compared with other Al2O3‐Si2 compositions. Based on the results of nitrogen adsorption/condensation, helium displacement, high‐resolution transmission electron microscopy (HRTEM), small‐angle X‐ray scattering (SAXS), and small‐angle neutron scattering (SANS), we attribute the low surface area and skeletal density (density of the solid phase which is inaccessable to helium) to the formation of closed micropores, whereas the higher surface area materials exhibit a slightly coarser texture comprising open pores with radii of ≅1 nm. X‐ray diffraction (XRD) and 29SI and 27Al magic‐angle spinning nuclear magnetic resonance (MASNMR) indicate no anomalous behavior in the 47% sample on molecular length scales. HRTEM indicates the presence of a small fraction of crystallites which is supported by the SAXS results, but it is unknown if this crystallinity is related to low surface area. Low‐field 1H NMR spin‐lattice relaxation measurements show that the physical structure of all of the ‘wet’ gels is similar implying that pore closure occurs during drying. Consistent with this idea, gel surface area and density increased significantly when the pore fluid (water) was replaced with a lower surface tension fluid (formamide, dioxane, ethanol. water/surfactant).
Reaction of Ammonia with Fumed Silica
Authors: Wusirika Raja
Published: March 2005

The reaction between fumed silica and ammonia has been studied between 600° and 1200°C. Up to 24 wt% nitrogen can be introduced into vitreous silica by adjusting the partial pressure of ammonia, temperature, and reaction time. The experiments show that the amount of nitrogen incorporated into silica has a linear dependence on the partial pressure of ammonia and a square root dependence on the reaction time. The activation energy for the reaction was found to be 76.0 kJ/mol. The nitrided powders as well as several hotpressed samples were crystallized at 1550° to 1650°C. Silica glasses containing 0 to 1 wt% nitrogen crystallize to cristobalite. Glasses containing 2 to 10 wt% nitrogen are stable against devitrification in nitrogen, even at 1650°C. Glasses with 12 to 28 wt% nitrogen crystallize to fine‐grained Si2N2O with residual glass.
Toughening Mechanisms in Cemented Carbides
Authors: Marshall David B. , Morris Winfred L. , Cox Brian N. , Dadkhah Mahyar S.
Published: March 2005

Plastic zones much larger than previously expected have been observed around cracks in several cemented carbide materials. A preliminary estimate of the crack tip shielding due to the plastic zone in one material suggests that a substantial fraction of the fracture toughness may be due to the zone. Moreover, reduced zone sizes were observed in regions of rapid crack growth, implying that the dynamic fracture toughness may be smaller than the quasi‐static value.
Microstructural and Chemical Influences of Silicate Grain‐Boundary Phases in Yttria‐Stabilized Zirconia
Authors: Lin Yung‐Jen , Angelini Peter , Mecartney Martha L.
Published: March 2005

The microstructure and chemistry of grain‐boundary phases in silicate‐doped Y2O3─ZrO2 ceramics were evaluated by analytical electron microscopy. Two different silicate compositions were used: one an aluminosilicate and the other a borosilicate glass. These grain‐boundary phases had a significant impact on the grain morphology, the chemical composition of the grains, and the crystallization of second phases. These results indicate that controlled additions of specific glass phases may provide a means for tailoring the microstructure and physical properties of zirconia ceramics.
Residual Stresses in Alumina/Silicon Carbide (Whisker) Composites by X‐ray Diffraction
Authors: Abuhasan Alias , Balasingh Chelleyan , Predecki Paul
Published: March 2005

Residual strains and stresses were determined in hot‐pressed α‐Al2O3 composites containing 29, 18, and 10 vol%β‐SiC whiskers using X‐ray diffraction. A 29 vol% SiC hot‐pressed specimen containing whiskers coated with a 5‐ to 10‐nm‐thick carbon film was also investigated. Strains were determined from the 511 and 333 reflections from SiC and the 146 reflection from Al2O3 using CuKα radiation and applying both the sin2Ω and generalized least‐squares methods. The total residual stresses were obtained from the least‐squares strains and were further separated into macrostresses and microstresses in each phase using the method of Noyan and Cohen. An error analysis of the strains and stresses was also performed. The average microstresses in the Al2O3 matrix were nearly hydrostatic and decreased with decreasing volume percent of SiC as follows: 397, 222, and 94 MPa for 29, 18, and 10 vol% SiC, respectively. The average microstresses in the whiskers were hydrostatic and were ‐958, ‐1058, and ‐979 MPa for 29, 18, and 10 vol% SiC, respectively. The presence of the carbon film decreased the magnitudes of the microstresses by about 10% and 5%, respectively, for the whiskers and the matrix. The X‐ray penetration depth was large (60 to 100 μm) compared with the whisker dimensions, so that the microstresses were representative of the bulk. The measured strains and microstresses were compared with those predicted by the models of Li and Bradt, Hsueh et al., and Majumdar et al., and with strains measured by neutron diffraction. In general, the agreement with the models and among the models was satisfactory, although the small decrease in the measured SiC microstresses in going from 18 to 10 vol% SiC was not predicted. The measured macrostresses were small (<140 MPa tensile), as expected from the light surface grinding of the surfaces (prepared using MIL standard 1942‐A).
Quantitative Analysis of High‐Alumina Refractories Using X‐ray Powder Diffraction Data and the Rietveld Method
Authors: Madsen Ian C. , Finney Russell J. , Flann Robert C. A. , Frost Malcolm T. , Wilson Bill W.
Published: March 2005

Quantitative determination of phase abundance in high‐alumina refractories has been performed using the Rietveld refinement method applied to X‐ray powder diffraction data. The use of a “whole‐pattern” method for analysis has allowed the simultaneous determination of accurate unitcell parameters and the phase abundance of major (mullite and cristobalite) and minor (quartz, corundum, and andalusite) phases. A comparison of the accurate unit‐cell parameters, produced during refinement, with published data has allowed the composition of mullite to be estimated at 3:2 Al2O3:SiO2. Cristobalite has been shown to be present in two distinct forms, both of which have been quantified in spite of severe overlap in their diffraction patterns. There is excellent agreement between SiO2 and Al2O3 contents calculated from the measured phase contents and those measured by X‐ray fluorescence spectrometry. The addition of fluorite in a known amount as an internal standard has allowed the estimation of the amount of amorphous material present.
Nitridation Kinetics and Thermodynamics of Silicon Powder Compacts
Authors: Barsoum Michel , Kangutkar Pramod , Koczak Michael J.
Published: March 2005

The nitridation kinetics of Si powder compacts were studied by measuring the flow rate dependence of N2 and N2–H2 gas mixtures during slow heating of Si compacts while simultaneously monitoring the oxygen partial pressure of the egress gas. The reaction was found to occur in two distinct stages. In pure nitrogen the initial stage was interpreted in terms of devitrification of the native silica layer, catalyzed by Fe impurities, and the exposure of the underlying Si. The reaction sequence at that point has been unequivocally shown to be

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followed by the formation of oxynitride according to

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as evidenced by a large increase in the oxygen partial pressure simultaneously with the onset of the initial stage. In the absence of hydrogen, both reactions are rapidly suppressed as the oxygen liberated competes with the nitrogen for the exposed silicon surface and reoxidizes it. However, in the presence of hydrogen, the oxygen liberated reacts with the hydrogen and prevents the reoxidation of the Si. The net reaction in this case is

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and/or

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with the second reaction being thermodynamically favored. The main nitridation reaction occurring between 1300° and 1400°C appears to be diffusion controlled and depends on the nature of the passivating layer that forms during the initial stage.
X‐ray Photoelectron Spectroscopy Study of High‐ and Low‐Temperature Forms of Zirconium Titanate
Authors: Ikawa Hiroyuki , Yamada Toshiyuki , Kojima Kenji , Matsumoto Shigeo
Published: March 2005

X‐ray photoelectron spectroscopy (XPS) spectra were measured for the high‐temperature forms (quenched from 1500°C) of zirconium titanate and its solid solutions, the low‐temperature forms (quenched from 1000°C), and cubic Ba(Zr1/2Ti1/2)O3. Two distinct differences in the XPS spectra were noted between the high‐ temperature forms. The O 1s spectrum of the high‐temperature form consisted of two peaks of nearly equal intensities with a spacing of 2.2 eV, which was larger than the corresponding spacing of 1.6 eV, for Ba(Zr1/2Ti1/2)O3, while the spectrum of the low‐temperature forms was almost a single peak. The high‐temperature form had an unassignable spectrum with a binding energy of 25 eV between the peaks of Zr 4p and O 2s. The unassignable spectrum could be a molecular orbital which had been hypothesized to form in these compounds.
Thin‐Layer Dielectrics in the Pb[(Mg1/3Nb2/3)1‐xTix]O3 System
Authors: Francis Lorraine Falter , Payne David A.
Published: March 2005

Thin layers of Pb[(Mg1/3Nb2/3)1–xTix]O3 (PMNT) were prepared by spin casting alkoxide‐based solutions on platinized Si. The effects of additives, heat treatment, and composition (x= 0 to 0.9) on perovskite phase development, ceramic microstructure, and dielectric properties are reported. Depending upon the processing conditions, ceramic thin layers could be formed in a nonferroelectric pyrochlore phase (A2B2O6) or in a ferroelectric perovskite phase (ABO3). The dimensions of the pyrochlore and perovskite units cells were related and increased with Mg and Nb contents. To minmize pyrochlore formation, the most effective processing method involved rapid heat treatment between successive solution depositions. Phase development and microstructure were also affected by solution additives. Additions of benzoic acid were found to affect the structure in solution and the later organic pyrolysis behavior from thin layers. The effect of composition on the dielectric and ferroelectric properties is also reported.
Steady‐State Mechanics of Delamination Cracking in Laminated Ceramic‐Matrix Composites
Authors: Charalambides Panos G.
Published: March 2005

A fracture mechanics delamination cracking model has been developed for brittle‐matrix composite laminates. The near‐tip mechanics is discussed in the context of material orthotropy and composite material inhomogeneities. A fracture mechanics framework based on the near‐tip energy release rate 𝒢 and the associated phase angle Ψ has been adopted. In the case of steady‐state delamination cracking in a prenotched cross‐ply symmetric laminated beam, analytical expressions for the steady‐state energy release rate, 𝒢ss, have been obtained for the combined applied loading of an axial force and a bending moment. Parameter studies assessing the effects on 𝒢ss of load coupling, crack location, and lamination morphology which includes the total number of layers, layer thickness, and material properties are presented. Thus, composite homogenization criteria with respect to the total number of layers placed along the beam height can be obtained for a wide range of material selection. The associated phase angle Ψ at the delamination crack tip is discussed in the context of existing solutions. The analysis has been developed based on a theory for structural laminates. The delamination model can be used in conjunction with experimental data obtained from model geometries to extract the mixed‐mode transverse composite fracture toughness. Thus, conditions for stable delamination crack growth can be established and design criteria based on toughness for composite laminates and composite fasteners can be obtained.
Mullitization of Diphasic Aluminosilicate Gels
Authors: Sundaresan Sankaran , Aksay Ilhan A.
Published: March 2005

Recent studies have shown that the mullitization of diphasic aluminosilicate matrices comprising transitional alumina and amorphous silica occurs via a nucleation and growth process. Nucleation is preceded by a temperature‐dependent incubation period. Following this incubation period, rapid nucleation of mullite occurs, producing about 1.8 × 1011 nuclei/cm3, which remains constant throughout the rest of the transformation. Both incubation and mullite growth are thermally activated processes with apparent activation energies of 987 ± 63 and 1070 ± 200 kJ/mol, respectively. The growth rate of mullite grains under isothermal conditions is time dependent. An interpretation of these results is proposed on the basis of the nucleation and growth concepts of LaMer and Dinegar which supports the concept that the growth rate of mullite grains is controlled by the dissolution of transitional alumina into the amorphous matrix.