bluuebunny/crossref_metadata_2025 huggingface dataset:
Positional averaging explains crowding with letter-like stimuli
Authors: Greenwood John A. , Bex Peter J. , Dakin Steven C.
Published: July 2009

Visual crowding is a breakdown in object identification that occurs in cluttered scenes, a process that represents the principle restriction on visual performance in the periphery. When crowded objects are presented experimentally, a key finding is that observers frequently report nearby flanking items instead of the target. This observation has led to the proposal that crowding reflects increased noise in the positional code for objects; although how the presence of nearby objects might disrupt positional encoding remains unclear. We quantified this disruption using cross-like stimuli, where observers judged whether the horizontal target line was positioned above or below the stimulus midpoint. Overall, observers were poorer at judging position in the presence of crowding flankers. However, offsetting horizontal lines in the flankers also led observers to report that the horizontal line in the target was shifted in the same direction, an effect that held for subthreshold flanker offsets. In short, crowding induced both random and systematic errors in observers' judgment of position, with or without the detection of flanker structure. Computational modeling reveals that perceived position in the presence of flankers follows a weighted average of noisy target- and flanker-line positions, rather than a substitution of flanker-features into the target, as has been proposed previously. Together, our results suggest that crowding is a preattentive process that uses averaging to regularize the noisy representation of position in the periphery.
The boundaries of language and thought in deductive inference
Authors: Monti Martin M. , Parsons Lawrence M. , Osherson Daniel N.
Published: July 2009

Is human thought fully embedded in language, or do some forms of thought operate independently? To directly address this issue, we focus on inference-making, a central feature of human cognition. In a 3T fMRI study we compare logical inferences relying on sentential connectives (e.g., not, or, if … then) to linguistic inferences based on syntactic transformation of sentences involving ditransitive verbs (e.g., give, say, take). When contrasted with matched grammaticality judgments, logic inference alone recruited “core” regions of deduction [Brodmann area (BA) 10p and 8m], whereas linguistic inference alone recruited perisylvian regions of linguistic competence, among others (BA 21, 22, 37, 39, 44, and 45 and caudate). In addition, the two inferences commonly recruited a set of general “support” areas in frontoparietal cortex (BA 6, 7, 8, 40, and 47). The results indicate that logical inference is not embedded in natural language and confirm the relative modularity of linguistic processes.
A model for DNA polymerase switching involving a single cleft and the rim of the sliding clamp
Authors: Heltzel Justin M. H. , Maul Robert W. , Scouten Ponticelli Sarah K. , Sutton Mark D.
Published: July 2009

The actions of
Escherichia coli
DNA Polymerase IV (Pol IV) in mutagenesis are managed by its interaction with the β sliding clamp. In the structure reported by Bunting et al. [
EMBO J
(2003) 22:5883–5892], the C-tail of Pol IV contacts a hydrophobic cleft on the clamp, while residues V303–P305 reach over the dimer interface to contact the rim of the adjacent clamp protomer. Using mutant forms of these proteins impaired for either the rim or the cleft contacts, we determined that the rim contact was dispensable for Pol IV replication in vitro, while the cleft contact was absolutely required. Using an in vitro assay to monitor Pol III*-Pol IV switching, we determined that a single cleft on the clamp was sufficient to support the switch, and that both the rim and cleft contacts were required. Results from genetic experiments support a role for the cleft and rim contacts in Pol IV function in vivo. Taken together, our findings challenge the toolbelt model and suggest instead that Pol IV contacts the rim of the clamp adjacent to the cleft that is bound by Pol III* before gaining control of the same cleft that is bound by Pol III*.
An algorithm for learning maximum entropy probability models of disease risk that efficiently searches and sparingly encodes multilocus genomic interactions
Authors: Miller David J. , Zhang Yanxin , Yu Guoqiang , Liu Yongmei , Chen Li , Langefeld Carl D. , Herrington David , Wang Yue
Published: July 2009

Motivation: In both genome-wide association studies (GWAS) and pathway analysis, the modest sample size relative to the number of genetic markers presents formidable computational, statistical and methodological challenges for accurately identifying markers/interactions and for building phenotype-predictive models.

Results: We address these objectives via maximum entropy conditional probability modeling (MECPM), coupled with a novel model structure search. Unlike neural networks and support vector machines (SVMs), MECPM makes explicit and is determined by the interactions that confer phenotype-predictive power. Our method identifies both a marker subset and the multiple k-way interactions between these markers. Additional key aspects are: (i) evaluation of a select subset of up to five-way interactions while retaining relatively low complexity; (ii) flexible single nucleotide polymorphism (SNP) coding (dominant, recessive) within each interaction; (iii) no mathematical interaction form assumed; (iv) model structure and order selection based on the Bayesian Information Criterion, which fairly compares interactions at different orders and automatically sets the experiment-wide significance level; (v) MECPM directly yields a phenotype-predictive model. MECPM was compared with a panel of methods on datasets with up to 1000 SNPs and up to eight embedded penetrance function (i.e. ground-truth) interactions, including a five-way, involving less than 20 SNPs. MECPM achieved improved sensitivity and specificity for detecting both ground-truth markers and interactions, compared with previous methods.

Availability:  http://www.cbil.ece.vt.edu/ResearchOngoingSNP.htm

Contact:  djmiller@engr.psu.edu

Supplementary information:  Supplementary data are available at Bioinformatics online.
Reconstructing spatiotemporal gene expression data from partial observations
Authors: Cartwright Dustin A. , Brady Siobhan M. , Orlando David A. , Sturmfels Bernd , Benfey Philip N.
Published: July 2009

Motivation: Developmental transcriptional networks in plants and animals operate in both space and time. To understand these transcriptional networks it is essential to obtain whole-genome expression data at high spatiotemporal resolution. Substantial amounts of spatial and temporal microarray expression data previously have been obtained for the Arabidopsis root; however, these two dimensions of data have not been integrated thoroughly. Complicating this integration is the fact that these data are heterogeneous and incomplete, with observed expression levels representing complex spatial or temporal mixtures.

Results: Given these partial observations, we present a novel method for reconstructing integrated high-resolution spatiotemporal data. Our method is based on a new iterative algorithm for finding approximate roots to systems of bilinear equations.

Availability: Source code for solving bilinear equations is available at http://math.berkeley.edu/∼dustin/bilinear/. Visualizations of reconstructed patterns on a schematic Arabidopsis root are available at http://www.arexdb.org/.

Contact:  dustin@math.berkeley.edu

Supplementary information:  Supplementary data are available at Bioinformatics online.
Calorie restriction and the exercise of chromatin
Authors: Vaquero Alejandro , Reinberg Danny
Published: July 2009

Since the earliest stages of evolution, organisms have faced the challenge of sensing and adapting to environmental changes for their survival under compromising conditions such as food depletion or stress. Implicit in these responses are mechanisms developed during evolution that include the targeting of chromatin to allow or prevent expression of fundamental genes and to protect genome integrity. Among the different approaches to study these mechanisms, the analysis of the response to a moderate reduction of energy intake, also known as calorie restriction (CR), has become one of the best sources of information regarding the factors and pathways involved in metabolic adaptation from lower to higher eukaryotes. Furthermore, responses to CR are involved in life span regulation—conserved from yeast to mammals—and therefore have garnered major research interest. Herein we review current knowledge of responses to CR at the molecular level and their functional link to chromatin.
Relaxation of selective constraints on avian mitochondrial DNA following the degeneration of flight ability
Authors: Shen Yong-Yi , Shi Peng , Sun Yan-Bo , Zhang Ya-Ping
Published: July 2009

The evolution of flight is the most important feature of birds, and this ability has helped them become one of the most successful groups of vertebrates. However, some species have independently lost their ability to fly. The degeneration of flight ability is a long process, and some species remain transitional locomotive models. Most of the energy required for locomotion is supplied by mitochondria via oxidative phosphorylation. Thus, rapidly flying birds should require a more energy efficient metabolism than weakly flying or flightless species. Therefore, we speculated that evolutionary constraints acted on the mtDNA of birds with different locomotive abilities. To test this hypothesis, we compared 76 complete avian mitochondrial genomes. Weakly flying and flightless birds, compared to rapidly flying birds, accumulated more nonsynonymous nucleotide substitutions relative to synonymous substitutions. Even after controlling for mutation rate, this trend remained significant. This finding was further tested for its generality by examining 214 complete mammalian mitochondrial genomes. The same as birds, a negative correlation was also found for theKa/Ksratio and locomotive speed. Our results demonstrated that, in addition to the previously described role for effective population size, functional constraints due to locomotion play an important role in the evolution of mtDNA.
Marketing the academic library on the web
Authors: Kaur Kiran
Published: July 2009

Purpose

The purpose of this paper is to describe the marketing initiatives taken by academic libraries to promote collection and services to their clientele. It specifically aims to examine academic library web sites for marketing approach, promotional and public relations activities.

Design/methodology/approach

The study relies heavily on web site exploration and interviews with library managers. A total of 22 library web sites were examined based on pre‐determined criteria developed from the extant literature and initial web site investigation. The paper also draws upon the authors' personal experiences and observations. Interviews were used to investigate university library manager's level of awareness of the library web site as a marketing tool and how they perceived this to be used to the library's advantage.

Findings

It is found that academic libraries are lacking in their promotional activities. Library web sites are not fully utilized as a marketing tool and an enabler to reach out to the community for promotion of services and collections.

Research limitations/implications

The study is limited to Malaysian university libraries, therefore generalization to others is to be cautioned but there are important lessons to be learnt.

Practical implications

This paper will be helpful to libraries planning to implement a marketing strategic plan to improve its outreach to users and enhance the users' image of the library.

Originality/value

A study such as this is new in Malaysia and reveals several marketing strategies that may be useful to other academic libraries.
A theoretical model of transformational leadership's role in diverse teams
Authors: Mitchell Rebecca J. , Boyle Brendan
Published: July 2009

Purpose

The purpose of this paper is to develop a theoretical model of leadership and knowledge creation by drawing on two contrasting diversity perspectives. The model argues a moderating role for leadership in explaining the influence of diverse composition on team knowledge creation.

Design/methodology/approach

A model of leadership's impact on knowledge creation is developed based on an interdisciplinary review of literature spanning the creativity, innovation and learning literature, diversity management, top management team demography and upper echelons literature and learning from transformational leadership research.

Findings

The main contribution of this paper is the development of a model of transformational leadership's impact on knowledge creation in diverse teams based on a series of propositions. Focusing on the information/decision‐making perspective, our model depicts the role of leadership in facilitating constructive cognitive effects on knowledge creation. From the social categorisation perspective our model depicts the role of leadership in mitigating against destructive emotional barriers to group effectiveness.

Research limitations/implications

This paper's review and model indicate significant implications for future research and practice. The model provides a better understanding of the effects of transformational leadership on knowledge creation. The paper present justification for two pathways, cognitive and affective, through which leadership moderates the impact of diversity on team outcomes. By examining the model and its proposed relationships, we believe that it will enable researchers to shed new light on these issues for further investigations.

Originality/value

This review is among the first to address the role of transformational leadership in diverse teams, and one of the only papers to connect leadership, diversity and knowledge creation.
Sisterhood in short supply in the workplace
Authors: Marques Joan
Published: July 2009

Purpose

The purpose of this paper is to put forward the view that the glass ceiling will remain in place so long as women continue to hinder the progress of their female colleagues in the workplace.

Design/methodology/approach

Presents three examples of women who held back the advancement of their female colleagues.

Findings

Highlights the “crab‐bucket” mentality, where crabs at the bottom of a bucket pull down the ones that try to climb up.

Practical implications

Suggests that this behavior may partially be explained by the fact that women may have to work harder for promotion.

Originality/value

Provides a new insight on the glass ceiling.
Assessing the nomological validity of a cognitive age segmentation of Japanese seniors
Authors: Van Auken Stuart , Barry Thomas E.
Published: July 2009

Purpose

The purpose of this paper is to use cognitive age to segment college‐educated Japanese seniors, a grouping of interest to many marketers both within and external to Japan. The intent is to demonstrate the nomological validity of the cognitive age concept by relating it to key externalities and to further assess the viability of cognitive age over chronological age in non‐Western segmentation research.

Design/methodology/approach

Both hierarchical and non‐hierarchical clustering are employed to form segments of Japanese seniors based on their average cognitive age, as revealed by both Likert and semantic‐differential scaling. Differences are sought between the two clusters on key segmentation variables.

Findings

The results reveal that Japanese seniors who are younger, psychologically speaking, have more positive attitudes toward life satisfaction and aging than those respondents who are cognitively older. The psychologically younger respondents also tend to be more involved in activities and have better health along with economic comfort. The study further demonstrates, in a non‐Western setting, the predictive power of cognitive age over chronological age since the revealed cognitive age segments have the same chronological age.

Practical implications

The fact that average cognitive age relates to one's health makes it a powerful segmentation variable in international segmentation research on the mature market. Basically, cognitive age reveals an aptitude and, when coupled with purchasing power, the viability of senior segments may be assessed more clearly and strategically.

Originality/value

The study validates the usefulness of cognitive age in global segmentation research and illustrates its potential as a better predictor of behavior than chronological age.
Processing of High‐Density Submicrometer Al2O3 for New Applications
Authors: Krell Andreas , Blank Paul , Ma Hongwei , Hutzler Thomas , Nebelung Manfred
Published: July 2009

Sintered corundum components with submicrometer grain sizes exhibit properties which enable numerous new applications. Wet powder processing is developed to associate minimum grain sizes at highest densities with the lowest population of macrodefects. A closest ratio of powder particle size and sintered grain size is important for obtaining most fine‐grained microstructures. This target was approached best by using powders with particle sizes in the range of 100–200 nm rather than with smaller nanoparticles.
Synthesis and Characterization of Lead Zirconate Titanate Fibers Prepared by the Sol–Gel Method: The Role of the Acid
Authors: Zhang Mei , Salvado I. M. Miranda , Vilarinho Paula M.
Published: July 2009

Lead zirconate titanate (PZT) fibers are prepared by the sol–gel method using acetic acid and methacrylic acid to control the pH of the PZT precursor sol. The chemical evolution of the precursors, the thermal and crystallization behavior of the PZT gel fibers, and the microstructure of the samples with and without acid addition are analyzed and compared. It is observed that the properties of the fibers are improved when acids are used; particularly longer PZT ceramic fibers (4–5 cm) are obtained after heat treatment and a single perovskite phase is obtained at 550°C when using methacrylic acid. The mechanisms of the acid effect on the strengthening and crystallization of PZT fibers are discussed.
Effect of Carbon and Silicon Carbide/Carbon Interlayers on the Mechanical Behavior of Tyranno‐SA‐Fiber‐Reinforced Silicon Carbide‐Matrix Composites
Authors: Yang Wen , Kohyama Akira , Katoh Yutai , Araki Hiroshi , Yu Jinnan , Noda Tetsuji
Published: July 2009

Several CVI‐SiC/SiC composites were fabricated and the mechanical properties were investigated using unloading–reloading tensile tests. The composites were reinforced with a new Tyranno‐SA fiber (2‐D, plain‐woven). Various carbon and SiC/C layers were deposited as fiber/matrix interlayers by the isothermal CVI process. The Tyranno‐SA/SiC composites exhibited high proportional limit stress (∼120 MPa) and relatively small strain‐to‐failure. The tensile stress/strain curves exhibited features corresponding to strong interfacial shear and sliding resistance, and indicated failures of all the composites before matrix‐cracking saturation was achieved. Fiber/matrix debonding and relatively short fiber pullouts were observed on the fracture surfaces. The ultimate tensile strength displayed an increasing trend with increasing carbon layer thickness up to 100 nm. Further improvement of the mechanical properties of Tyranno‐SA/SiC composites is expected with more suitable interlayer structures.
High‐Resolution Transmission Electron Microscopy Study of the Microstructural Development of a Silicon Carbonitride Nanocomposite
Authors: Wan Julin , Gasch Matthew J. , Lesher Charles E. , Mukherjee Amiya K.
Published: July 2009

Nanocrystalline ceramics are expected to possess enhanced superplasticity over their microcrystalline counterparts. In this effort of producing nanocomposites of silicon nitride and silicon carbide, amorphous Si‐C‐N derived from pyrolysis of a polysilazane precursor was sintered with yttria as an additive. High‐pressure sintering at different temperatures resulted in sintered materials ranging from amorphous to nanocrystalline. High‐resolution transmission electron microscopy was conducted to characterize the development and grain‐boundary features of the nanocrystalline microstructure. The results provide a preliminary understanding of the process of the formation of the nanocrystalline structure from an amorphous matrix, under the condition of high pressure and relatively low temperature. The wide variation in the thickness of grain‐boundary phases observed in this material suggests a nonequilibrium state of the grain boundary, which might be related to the processing conditions.
Effect of Rigid Inclusions on the Densification and Constitutive Parameters of Liquid‐Phase‐Sintered YBa2Cu3O6+x Powder Compacts
Authors: Salamone Samuel M. , Stearns Laura C. , Bordia Rajendra K. , Harmer Martin P.
Published: July 2009

The presence of rigid inclusions in a powder compact leads to a reduction in the densification rate of the compact and may also lead to processing defects. In this paper, the densification rate and the constitutive parameters of both homogeneous YBa2Cu3O6+x and composite powder compacts (YBa2Cu3O6+x powder with 10 vol% dense inclusions of YBa2Cu3O6+x) are reported. A small amount of liquid phase, which formed during sintering, was present in the samples. However, even with the presence of a liquid phase, the addition of inclusions still reduces the densification rate of the composite and increases its viscosity. The results have been compared with a published analysis of the problem using measured values of the constitutive parameters. Both the viscosity and viscous Poisson's ratio of the porous body have been measured.
Subsolidus Phase Relationships in the System Fe2O3–Al2O3–TiO2 between 1000° and 1300°C
Authors: Pownceby Mark I. , Constanti‐Carey Keri K. , Fisher‐White Michael J.
Published: July 2009

Subsolidus phase equilibria in the system Fe2O3–Al2O3–TiO2 were investigated between 1000° and 1300°C. Quenched samples were examined using powder X‐ray diffraction and electron probe microanalytical methods. The main features of the phase relations were: (a) the presence of an M3O5 solid solution series between end members Fe2TiO5 and Al2TiO5, (b) a miscibility gap along the Fe2O3–Al2O3 binary, (c) an α‐M2O3(ss) ternary solid‐solution region based on mutual solubility between Fe2O3, Al2O3, and TiO2, and (d) an extensive three‐phase region characterized by the assemblage M3O5+α‐M2O3(ss) + Cor(ss). A comparison of results with previously established phase relations for the Fe2O3–Al2O3–TiO2 system shows considerable discrepancy.
Low‐Temperature Synthesis of Nanocrystalline Yttrium Aluminum Garnet Powder Using Triethanolamine
Authors: Liu Yangqiao , Gao Lian
Published: July 2009

Nanocrystalline yttrium aluminum garnet (YAG, Y3Al5O12) was synthesized by pyrolysis of complex compounds of aluminum and yttrium with triethanolamine [(HOCH2CH2)3N, (TEA)]. Loose and porous precursor was obtained on complete dehydration of the metal ion–triethanolamine complexes. Pure YAG powder was obtained by calcination of the precursor at 950°C. The precursor was characterized by simultaneous thermogravimetry, differential scanning calorimetry, and mass spectra analyses (TG–DSC–MS). The heat‐treated powders were characterized by X‐ray diffractometry (XRD), specific surface area measurements, and transmission electron microscopy (TEM). The average crystallite size as determined from X‐ray line broadening and transmission electron microscopy studies was ∼40 nm. The effects of the calcination temperature and the ratio of triethanolamine to mixed metal ions were also studied.
Chemical Solution Deposition of Columnar‐Grained Metallic Lanthanum Nitrate Thin Films
Authors: Cheng Jian‐Gong , Gabl Reinhard , Pitzer Dana , Primig Robert , Schreiter Matthias , Wersing Wolfram
Published: July 2009

Columnar and (100)‐oriented LaNiO3 thin films were prepared on silicon substrates by a chemical solution deposition (CSD) process using a 0.05M solution. By reducing the individual layer thickness to 10 nm, columnar LaNiO3 films with a lateral grain size of ∼120 nm were obtained. The success of this approach required restricting the individual layer thickness to a value below the grain size observed for equiaxed films. This change in microstructure resulted in an improvement in conductivity. The columnar LaNiO3 film with a thickness of 300 nm showed a resistivity of 4.5 × 10−5Ω·cm, which is lower by one order of magnitude than that of fine‐grain equiaxed films that typically result from CSD methods.
Thermal Stability of a Chemically Vapor Deposited Multilayer Coating Containing Amorphous Silica and Rutile Titania on Hi‐Nicalon Fiber
Authors: Lee Jinil , Li Hao , Lee Woo Y.
Published: July 2009

A multilayer coating consisting of consecutive layers of amorphous‐silica, rutile‐titania, and amorphous‐silica was prepared on Hi‐Nicalon fiber by chemical vapor deposition at 1050°C. It appeared that the silica and titania layers were strongly bonded to each other with no evidence of detachment and crack deflection at the interface region. The layered structure became morphologically unstable because of the growth of titania grains, the crystallization of the silica layers, and the oxidation of the fiber on exposure to 1200°C in air for 92 h.
Preparation of Highly Dispersed Ultrafine Barium Titanate Powder by Using Microbial‐Derived Surfactant
Authors: Kamiya Hidehiro , Gomi Kenjiro , Iida Yuichi , Tanaka Kenji , Yoshiyasu Takashi , Kakiuchi Toshihito
Published: July 2009

To uniformly disperse ultrafine BaTiO3 particles with a stoichiometric composition and several tens of nanometers in diameter to primary particles during the sol–gel synthesis process, a new aqueous surfactant with a high hydrophilic group density and special cis‐structure was prepared from a microbial product and added to solution before the sol–gel synthesis reaction. Because of the rapid formation of large and porous aggregates which were 30–50 μm in diameter in suspension without addition of this unique structural surfactant, the prepared ultrafine BaTiO3 particles caused rapid sedimentation in suspension. The addition of the surfactant in the range of 7.1 wt% for the synthesized BaTiO3 particles made it possible to decrease the size of the aggregates in suspension as well as the sedimentation velocity while maintaining the stoichiometric composition. The optimum additive content to obtain the minimum aggregate size of about 100–200 nm in diameter and the highest dispersion stability in suspension while maintaining the stoichiometric composition of prepared ultrafine BaTiO3 particles without other phases was determined at about 7.1 wt%. Because the excess addition of this surfactant at more than 8.5 wt% inhibited the uniform synthesis of BaTiO3 particles, an amorphous phase with a highly specific surface area and a BaCO3 phase formed in the synthesized particles.
Macrochanneled Tetragonal Zirconia Polycrystals Coated by a Calcium Phosphate Layer
Authors: Koh Young‐Hag , Kim Hae‐Won , Kim Hyoun‐Ee , Halloran John W.
Published: July 2009

A coextrusion process was used to fabricate three‐directionally macrochanneled tetragonal zirconia polycrystals (TZP) with a calcium phosphate coating layer. The three‐directionally connected structure was built by a unique alignment and a lamination of the TZP surrounded by calcium phosphate and carbon black filaments. After a thermal treatment (binder burnout and sintering), a 52 vol% array of 290 μm, three‐directionally connected macrochannels, which were clad on the inside with bioactive calcium phosphate, had formed on the sintered TZP body. For a comparison, porous calcium phosphate with a similar structure was also fabricated. The compressive strength (96 MPa) of the three‐directionally macrochanneled TZP with a bioactive calcium phosphate layer was much higher than that (24 MPa) of the three‐directionally macrochanneled calcium phosphate.
Dynamics of Formation of Self‐Organized Mesoporous AlO(OH)·αH2O Structure in Al‐Metal Surface Hydrolysis in Humid Air
Authors: Ram S.
Published: July 2009

In humid air, a nascent Al‐metal surface (S) with a surface Hg2+ catalyst hydrolyzes in divided reaction centers (micelles) with a vigorous exothermic reaction, {Al + 2OH−}+αH2O → AlO(OH)·αH2O + 3e−+ H+. It yields amorphous AlO(OH)·αH2O with a huge ∼90% porosity with α= 0.25. The primary driving forces of the reaction are the chemical potential μe between the reaction species, the mechanical stress ς induced in expansion of S, and the flow of the reaction species. They drive it in a common direction perpendicular to S. The heat released in it flows primarily along S. It disrupts and stops the directional hydrolysis if the local temperature in the micelle reaches a critical value Tc (hot spot). The hot spot cools to the operating value T0, and the reaction restarts and runs over to Tc in a periodic manner, at a time scale of Δti∼ 5 s, per the dynamics of hot spots, forming a self‐organized mesoporous structure of 15–50‐nm diameter ellipsoidal shaped particles (halo) separated through 3–5‐nm pores. A pore, in continuous formation of the sample, forms in disrupted reaction during the hot spot as it cools from Tc to T0. The result is modeled in terms of the microstructure and dynamics of the hot spots.
Influence of Carbon on SOx Emissions from Glass Processing
Authors: Samadhi Tjokorde W. , Jones Linda E. , Clare Alexis G.
Published: July 2009

Carbon reacts with Na2SO4 in glass batches, influencing SOx emissions. To study the role of carbon active surface area (ASA) in the decomposition phenomena, Na2SO4 is reacted with three carbons with a wide ASA range. The decomposition behavior was evaluated by thermogravimetric analysis (TGA) and evolved gas analysis via mass spectrometry and Fourier transform infrared spectrometry. Higher carbon ASA yields lower decomposition temperatures. SOx emissions are realized at temperatures as low as 773 K. Isothermal Na2SO4–C decomposition initiates via the nucleation of Na2S. The rate constants for the nucleation regime are normalized against ASA, yielding an activation energy of 275 kJ/mol for nucleation.
Fabrication of Macroporous Alumina with Tailored Porosity
Authors: Tang Fengqiu , Fudouzi Hiroshi , Sakka Yoshio
Published: July 2009

Macroporous alumina materials were fabricated via colloidal processing using polymer spheres as the template and ceramic particles as the building blocks. The influence of the suspension conditions and volume ratio of the polymer/ceramic particles on the formation of the pore structure has been investigated. The results showed that the suspension conditions have a significant effect on the pore morphology. A well‐defined three‐dimensional, ordered porous structure with a controllable pore size and porosity could be obtained through the hetero‐coagulation, self‐assembled processing of the polymer/ceramic particles. The pore size and porosity could be easily tailored by varying the polymer size and the volume ratio of the polymer/ceramic particles.
Hydrothermal Synthesis of Submicrometer α‐Alumina from Seeded Tetraethylammonium Hydroxide‐Peptized Aluminum Hydroxide
Authors: Yang Juan , Mei Sen , Ferreira José M. F.
Published: July 2009

Submicrometer α‐alumina powder was successfully synthesized from seeded aluminum hydroxide peptized with tetraethylammonium hydroxide (TENOH) and hydrothermally treated at 200°C, using α‐alumina particles as seeds. The powders were characterized by XRD, SEM, DTA‐TG, and BET analyses. Results showed that seeding could greatly enhance the transition to α‐alumina at 200°C without formation of other transient alumina phases. α‐Alumina with some amount of boehmite formed in the seeded samples, whereas boehmite was the exclusive phase formed in the nonseeded sample. The morphology of α‐alumina embedded in the boehmite matrix for the seeded samples suggests a direct transition from aluminum hydroxide to α‐alumina without the formation of transient alumina phases. The formation of α‐alumina in the seeded samples at temperatures as low as 200°C could be attributed to a favored nucleation in the TENOH‐peptized aluminum hydroxide and to the subsequent hydrothermal treatment that supplies the necessary activation energy for crystal growth. Transition of boehmite to α‐alumina in the hydrothermally treated samples with low‐seed contents was significantly promoted by heat‐treating the samples at 500°C.
Synthesis of Zinc Aluminate Spinel Film through the Solid‐Phase Reaction between Zinc Oxide Film and α‐Alumina Substrate
Authors: Bi Zhaoxia , Zhang Rong , Wang Xusheng , Gu Shulin , Shen Bo , Shi Yi , Liu Zhiguo , Zheng Youdou
Published: July 2009

We synthesized spinel ZnAl2O4 film on α‐Al2O3 substrate using a solid‐phase reaction between the pulsed‐laser‐deposited ZnO film and α‐Al2O3 substrate. Auger electron spectroscopy showed that the atomic distribution in the spinel ZnAl2O4 was inhomogeneous, which indicated that the reaction was diffusion controlled. Based on X‐ray fluorescence measurements, the apparent growth activation energy of ZnAl2O4 was determined as 504 kJ/mol. X‐ray diffractometry spectra showed that, as the growth temperature increased, the ZnAl2O4 film became disoriented from the single (111) orientation. The ZnAl2O4 (333) diffraction peak shifted toward a small angle, and its full‐width at half‐maximum decreased from 1.30° to 0.37°. At the growth temperature of 1100°C, the morphology of the ZnAl2O4 was initially transformed from islands to stick structures, then to bulgy‐line structures with increased growth time. X‐ray diffractometry spectra showed that these transformations were correlated with changes of ZnAl2O4 orientation.
Simultaneous Synthesis and Densification of Titanium Oxycarbide, Ti(C,O), through Gas–Solid Combustion
Authors: Hashishin Takeshi , Yamamoto Takeshi , Ohyanagi Manshi , Munir Zuhair A.
Published: July 2009

The synthesis of titanium oxycarbide through a solid–gas combustion was investigated. Titanium powders containing TiC additive at levels ranging from 0 to 50 wt% were combusted in an atmosphere of carbon dioxide gas, at pressures ranging from 0.1 to 5.0 MPa. The characteristics of the synthesis process and the properties of the resulting product were found to depend on the level of the TiC additive and on the pressure of the carbon dioxide gas. Dense oxycarbides (∼96% relative density) with Vickers microhardness of ∼18 GPa were synthesized. In addition, the process presents a possible method for the fixation of carbon dioxide gas for the synthesis of useful materials.
Nanocrystalline Tin Oxide Thin Films via Liquid Flow Deposition
Authors: Supothina Sitthisuntorn , de Guire Mark R. , Heuer Arthur H.
Published: July 2009

Nanocrystalline films of SnO2 were deposited by liquid flow deposition (LFD), i.e., by flowing aqueous solutions of SnCl4·5H2O and HCl over single‐crystalline silicon substrates at 80°C. The substrates were either oxidized and fully hydrolyzed (bare silicon) or oxidized, hydrolyzed, and then coated with siloxy‐anchored organic self‐assembled monolayers (SAMs). Continuous, adherent films formed on sulfonate‐ and thioacetate‐functionalized SAMs; adherent but sometimes discontinuous films formed on bare silicon and methyl‐functionalized SAMs. The films contained equiaxed cassiterite crystals, ∼4–10 nm in size. The film thickness increased linearly with deposition time. The maximum growth rate observed was 85 nm·h−1 on sulfonate SAM, and the maximum film thickness obtained was 1 μm. A new dimensionless parameter, the normalized residence time, τ, was introduced for the purpose of interpreting the influence of solution conditions (i.e., degree of supersaturation, as controlled via pH, and tin concentration) and flow characteristics (flow rate and the configuration of the deposition chamber) on the growth rate in LFD processes. The results were consistent with a particle attachment mechanism for film growth and inconsistent with heterogeneous nucleation on the substrate.
Lanthanum‐Modified (1 – x)(Bi0.8La0.2)(Ga0.05Fe0.95)O3·xPbTiO3 Crystalline Solutions: Novel Morphotropic Phase‐Boundary Lead‐Reduced Piezoelectrics
Authors: Cheng Jin‐Rong , Eitel Richard , Cross L. Eric
Published: July 2009

(1 –x)(Bi0.8La0.2)(Ga0.05Fe0.95)O3·xPbTiO3 (BLGF‐PT) crystalline solutions have been fabricated by solid‐state reactions. BLGF‐PT has single perovskite phase structure with a rhombohedral–tetragonal (FEr‐FEt) morphotropic phase boundary (MPB) at a PT content of x= 0.43. Lanthanum substitution has been found to increase the insulation resistance and decrease the coercive field down to 20 kV/cm, which results in significant improvements in dielectric and piezoelectric properties of BLGF‐PT. The dielectric constant, loss tangent, Curie temperature, remnant polarization, piezoelectric d33 constant, and planar coupling factor of 1760, 0.05, 264°C, 33 μC/cm2, 295 pC/N, and 0.36, respectively, have been achieved for BLFG‐PT in the vicinity of the MPB. Compared with conventional Pb(Zr,Ti)O3 (PZT) piezoelectric ceramics, the BLGF‐PT is a competitive alternative piezoelectric material with decreased lead content.
Tensile Strength and Deformation of a Two‐Dimensional Carbon–Carbon Composite at Elevated Temperatures
Authors: Goto Ken , Hatta Hiroshi , Oe Masato , Koizumi Takashi
Published: July 2009

Tensile strength and creep behavior of a two‐dimensional (2D) laminate carbon–carbon composite (C/C) were examined from room temperature to 2773 K in an inert atmosphere. The tensile strength of the C/C was monotonically enhanced with increasing test temperatures. In particular, significant improvement was observed at temperatures higher than 1773 K. In this temperature range, nonlinear stress–strain curves were observed at low deformation rates, but with increasing test speed, the stress–strain curves became linear until total fracture. The source of the apparent nonlinearity was thus concluded to be creep deformation, which appeared from 1773 K. Two ruling mechanisms for the strength enhancement of the C/C at elevated temperatures were identified. The first source was degassing of absorbed water, which had a dominant influence on the strength enhancement up to 1773 K. The second was creep deformation. This phenomenon was notable at temperatures higher than 1773 K, and produced much larger enhancement than the degassing.
Crack‐Healing Behavior of Al2O3Toughened by SiC Whiskers
Authors: Takahashi Koji , Yokouchi Masahiro , Lee Sang‐Kee , Ando Kotoji
Published: July 2009

Al2O3reinforced by SiC whiskers (Al2O3/SiC‐W) was hot‐pressed to investigate the crack‐healing behavior. Semielliptical surface cracks of 100 μm in surface length were introduced using a Vickers indenter. The specimens containing precracks were crack‐healed at temperatures between 1000° and 1300°C for 1 h in air, and their strengths were measured by three‐point bending tests at room temperature and elevated temperatures between 400° and 1300°C. The results show that Al2O3/SiC‐W possesses considerable crack‐healing ability. The surface cracks with length of 2c= 100 μm could be healed by crack‐healing at 1200° or 1300°C for 1 h in air. Fracture toughness of the material was also determined. As expected, the SiC whiskers made their Al2O3tougher.
Hydration Products and Reactivity of Blast‐Furnace Slag Activated by Various Alkalis
Authors: Escalante‐García Jose I. , Fuentes Antonio F. , Gorokhovsky Alexander , Fraire‐Luna Pedro E. , Mendoza‐Suarez Guillermo
Published: July 2009

Pastes of blast‐furnace slag were cured for up to 90 d using sodium silicate (waterglass), NaOH, and three different mixtures of Na2CO3–Na2SO4–Ca(OH)2 to activate reactions. The highest slag reactivity was observed for NaOH activation and the least for waterglass, although nonevaporable water indicated similar amounts of hydration products formed. The main hydration products found using X‐ray diffractometry in all systems were calcium silicate hydrate (C‐S‐H) and a hydrotalcite‐type phase. Microanalysis was performed on pastes activated using 50% Na2CO3·25% Na2SO4·25% Ca(OH)2, NaOH, and waterglass; the chemical composition of the C‐S‐H in the waterglass case was different relative to the other two alkalis. For all alkaline agents used, the C‐S‐H seemed finely intermixed with a hydrotalcite‐type phase of Mg/Al = 1.82, on average.
X‐ray Diffraction Investigations of Microstructure of Calcium Hydroxide Crystallites in the Interfacial Transition Zone of Concrete
Authors: Harutyunyan Valeri S. , Abovyan Eduward S. , Monteiro Paulo J. M. , Mkrtchyan Vahram P. , Balyan Minas K. , Aivazyan Ashoi P.
Published: July 2009

This work presents theoretical and experimental X‐ray diffractometry investigations of the morphology and deformation state of calcium hydroxide (Ca(OH)2, CH) crystallites in the interfacial transition zone of concrete. Based on the developed theoretical approach, the distributions of CH crystallites and their coherent domains over strains and sizes are reconstructed. The average amounts of planar defects, cracks, and possible stacking faults within a CH crystallite are estimated. A comparative analysis is conducted for the morphology of CH texture depending on the type of aggregate particles (granite and smoky quartz) used.
Lead Zirconate Titanate Thin Films by Aerosol Plasma Deposition: Microstructure Analysis
Authors: Huang Ming‐Ren , Peng Cheng‐Jien , Lu Hong‐Yang
Published: July 2009

Lead zirconate titanate (Pb(Zr,Ti)O3, PZT) thin films were grown on silicon 〈100〉 substrate by aerosol plasma deposition (APD) using solid‐state‐reacted powder containing donor oxide Nb2O5 when keeping the substrate at room temperature and 200°C. Crystalline phases of the deposited films have been analyzed via X‐ray diffractometry (XRD), and microstructure via scanning and transmission electron microscopy (SEM and TEM). Cross‐sectional TEM revealed that the microstructure comprised several layers including the deposited PZT film and the platinum‐electrode‐and‐titanium‐buffered layers on SiO2–Si substrate. The Pt‐electrode layer contained (111)Pt twinned columnar grains with a slight misorientation and forming low‐angle grain boundaries among them. The PZT layer contained randomly oriented grains embedded in an amorphous matrix. Some of the PZT grains, oriented with the zone axis Z= [[Twomacr]11]PZT parallel to Z= [111]Pt, were grown epitaxially on the Pt layer by sharing the (111)PZT plane with the (111)Pt twinned columnar Pt crystals. However, the existence of such an orientation relationship was confined to several nanosize grains at and near the PZT‐Pt interface, and no gross film texture has been developed. An amorphous grain boundary phase, generated by pressure‐induced amorphisation (PIA) in the solid state, was identified by high‐resolution imaging. Its presence is taken to account for the densification of the PZT thin films via a sintering mechanism involving an amorphous phase on deposition at 25° and 200°C.
Influence of Excess PbO Additions on {111} Single‐Crystal Growth of Pb(Mg1/3Nb2/3)O3–35 mol% PbTiO3by Seeded Polycrystal Conversion
Authors: Khan Ajmal , Gorzkowski Edward P. , Scotch Adam M. , Leite Edson R. , Li Tao , Chan Helen M. , Harmer Martin P.
Published: July 2009

The influence of additions of excess PbO to Pb(Mg1/3Nb2/3)O3–35 mol% PbTiO3(PMN–35PT) on {111} single‐crystal growth by seeded polycrystal conversion was studied in the range of 0–5 vol% PbO. PbO volatilization and hence weight loss during annealing was controlled effectively by a double‐crucible type of arrangement. PbO additions increased boundary mobility significantly in PMN–35PT, thus facilitating single‐crystal growth by seeded polycrystal conversion (SPC). This is attributed to the formation of a boundary wetting PbO‐based liquid phase. The growth process occurs very rapidly initially, after which it slows down. This is presumably due to both a decrease in the driving force for boundary migration because of an increase in matrix grain size, and a transition to lower mobility facets. It is also shown that for a given annealing time, the size of the grown crystal scales with the lateral dimensions of the seed crystal.
Kinetics of {001} Pb(Mg1/3Nb2/3)O3–35 mol% PbTiO3 Single Crystals Grown by Seeded Polycrystal Conversion
Authors: King Patrick T. , Gorzkowski Edward P. , Scotch Adam M. , Rockosi Derrick J. , Chan Helen M. , Harmer Martin P.
Published: July 2009

The kinetics of {001}‐oriented Pb(Mg1/3Nb2/3)O3–35 mol% PbTiO3 (PMN–35PT) single crystals grown by seeded polycrystal conversion were systematically quantified as a function of excess PbO liquid phase. The coarsening behavior of the corresponding matrix grains was similarly quantified. Single‐crystal seed plates were embedded in a matrix of PMN‐35PT with varying amounts of liquid phase (PbO) content in the range of 0 to 5 vol% and annealed at 1150°C for 0–10 h. Apparent maxima in the growth rates were observed at a PbO content of ∼3 vol% for both the single crystal and matrix grains. In both cases, the growth data were found to most closely follow cubic growth kinetics. Implications regarding the effect of PbO volume fraction on the matrix and single‐crystal growth mechanisms are discussed.
Residual Stress Distributions in the Solid Solution Eutectic, Co1−xNixO/ZrO2(CaO)
Authors: Brewer L. N. , Peascoe R. A. , Hubbard C. R. , Dravid V. P.
Published: July 2009

This study investigates thermal mismatch stresses in the lamellar microstructure of the solid solution directionally solidified eutectic (DSE) oxide Co1−xNixO/ZrO2(CaO). X‐ray and neutron diffraction measurements were performed on isolated eutectic domains to measure the residual strain and stress tensors. Maximum principal residual stresses on the order of 1 GPa were recorded, with the Co1−xNixO and the ZrO2(CaO) phases maintaining states of tensile and compressive stress, respectively. The stress tensors for these materials are compared with measurements for similar DSE oxide systems and suggest that solid solution DSEs might be used to tailor the residual stress states in DSE composites.
A New Aluminum Coordination Site in Si‐C‐Al‐N‐(O) Ceramics
Authors: Li Xudong , Edirisinghe Mohan J.
Published: July 2009

A variety of Si‐C‐Al‐N‐(O) ceramics with different AlN and SiC contents were prepared by pyrolysis of Si‐Al‐C‐O precursors at 1700°C in nitrogen. In those ceramics containing small amounts of aluminum, a new 27Al MAS NMR peak at 134.3 ppm was found. The existence of this peak is discussed in relation to recent findings in aluminum‐containing complex ceramic systems.
Hydrothermal Synthesis of Thin Films of Barium Titanate Ceramic Nano‐Tubes at 200°C
Authors: Padture Nitin P. , Wei Xuezheng
Published: July 2009

A novel, low‐temperature synthesis method for producing BaTiO3 thin films patterned in the form of nano‐tubes (“honeycomb”) on Ti substrates is reported. In this two‐step method, the Ti substrate is first anodized to produce a surface layer (∼200–300‐nm thickness) of amorphous titanium oxide nano‐tube (∼100‐nm diameter) arrays. In the second step, the anodized substrate is subjected to hydrothermal treatment in aqueous Ba(OH)2, where the nano‐tube arrays serve as templates for their hydrothermal conversion to polycrystalline BaTiO3 nano‐tubes. This opens the possibility of tailoring the nano‐tube arrays and of using various precursor solutions and their combinations in the hydrothermal bath, to produce ordered, patterned thin‐film structures of various Ti‐containing ceramics. These could find use not only in a variety of electronic device applications but also in biomedical applications, where patterned thin films are also desirable.
Modeling of Porous Ceramics Response to Compressive Loading
Authors: Sadowski Tomasz , Samborski Sylwester
Published: July 2009

This paper deals with theoretical foundations of micromechanical constitutive modeling of porous polycrystalline ceramic materials under compression. The porosity of the material is assumed to be closed and distributed in grains and along grain boundaries. It strongly influences both material elastic features and microcrack growth. The deformation process includes elastic phase, dislocation band creation, and microcrack initiation, the crack‐development phase leading to crack kinking and finally to failure. As an example, the quasi‐static loading process of MgO ceramics is analyzed.