bluuebunny/crossref_metadata_2025 huggingface dataset:
Using Swift observations of prompt and afterglow emission to classify GRBs
Authors: O'Brien Paul T , Willingale Richard
Published: February 2007

We present an analysis of early Burst Alert Telescope and X-ray Telescope data for 107 gamma-ray bursts (GRBs) observed by the Swift satellite. We use these data to examine the behaviour of the X-ray light curve and propose a classification scheme for GRBs based on this behaviour. As found for previous smaller samples, the earliest X-ray light curve can be well described by an exponential, which relaxes into a power-law, often with flares superimposed. The later emission is well fit using a similar functional form and we find that these two functions provide a good description of the entire X-ray light curve. For the prompt emission, the transition time between the exponential and the power-law gives a well-defined time-scale,
T
p
, for the burst duration. We use
T
p
, the spectral index of the prompt emission,
β
p
, and the prompt power-law decay index,
α
p
, to define four classes of burst: short, slow, fast and soft. Bursts with slowly declining emission have spectral and temporal properties similar to the short bursts despite having longer durations. Some of these GRBs may therefore arise from similar progenitors including several types of binary system. Short bursts tend to decline more gradually than longer duration bursts and hence emit a significant fraction of their total energy at times greater than
T
p
. This may be due to differences in the environment or the progenitor for long, fast bursts.
Gamma-ray burst theory after Swift
Authors: Piran Tsvi , Fan Yi-Zhong
Published: February 2007

Afterglow observations in the pre-Swift era confirmed to a large extend the relativistic blast wave model for gamma-ray bursts (GRBs). Together with the observations of properties of host galaxies and the association with (type Ic) SNe, this has led to the generally accepted collapsar origin of long GRBs. However, most of the afterglow data was collected hours after the burst. The X-ray telescope and the UV/optical telescope onboard Swift are able to slew to the direction of a burst in real time and record the early broadband afterglow light curves. These observations, and in particular the X-ray observations, resulted in many surprises. While we have anticipated a smooth transition from the prompt emission to the afterglow, many observed that early light curves are drastically different. We review here how these observations are changing our understanding of GRBs.
The future of GRB investigation from ground and space
Authors: Piro Luigi
Published: February 2007

I will describe the prospects for future investigations of gamma-ray bursts (GRBs) in the ‘electromagnetic’ domain, by giving a brief overview of some near future facilities. I will discuss in some detail one of the most (if not the most) exciting perspective in the field, the use of GRBs as cosmological beacons.
Binary progenitor models for long-duration gamma-ray bursts
Authors: Podsiadlowski Philipp
Published: February 2007

While it is well established that long-duration gamma-ray bursts (LGRBs) are intrinsically rare events, requiring a special evolutionary channel, the nature of the most important channels still has to be established. Here, we review some of the main binary models that have been proposed, specifically tidal spin-up models and binary mergers of various types, and then present a new model involving the recently discovered mechanism of explosive common-envelope ejection. The latter model naturally explains why LGRB-related supernovae have not observed helium and may also explain a constant-density medium around LGRBs, as has been deduced in some cases. LGRB rates as well as their metallicity dependence is also discussed for the various models.
Magnetohydrodynamic simulations of the collapsar model for early and late evolution of gamma-ray bursts
Authors: Proga Daniel
Published: February 2007

I present results from magnetohydrodynamic (MHD) simulations of a gaseous envelope collapsing onto a black hole (BH). These results support the notion that the collapsar model is one of the most promising scenarios to explain the huge release of energy in a matter of seconds associated with gamma-ray bursts (GRBs). Additionally, the MHD simulations show that at late times, when the mass supply rate is expected to decrease, the region in the vicinity of the BH can play an important role in determining the rate of accretion, its time behaviour and ultimately the energy output. In particular, the magnetic flux accumulated around the BH can repeatedly stop and then restart the energy release. As proposed by Proga & Zhang, the episode or episodes of reoccurrence of accretion processes can correspond to X-ray flares discovered recently in a number of GRBs.
Gamma-ray bursts: cosmic rulers for the high-redshift universe?
Authors: Speirits Fiona C , Hendry Martin A , Gonzalez Alejandro
Published: February 2007

The desire to extend the Hubble Diagram to higher redshifts than the range of current Type 1a Supernovae observations has prompted investigation into spectral correlations in gamma-ray bursts (GBRs), in the hope that standard candle-like properties can be identified. In this paper, we discuss the potential of these new ‘cosmic rulers’ and highlight their limitations by investigating the constraints that current data can place on an alternative Cosmological model in the form of Conformal Gravity. By fitting current Type 1a Supernovae and GRB data to the predicted luminosity distance redshift relation of both the standard Concordance Model and the Conformal Gravity, we show that currently
neither
model is strongly favoured at high redshift. The scatter in the current GRB data testifies to the further work required if GRBs are to cement their place as effective probes of the cosmological distance scale.
GRB 030329: 3 years of radio afterglow monitoring
Authors: van der Horst A.J , Kamble A , Wijers R.A.M.J , Resmi L , Bhattacharya D , Rol E , Strom R , Kouveliotou C , Oosterloo T , Ishwara-Chandra C.H
Published: February 2007

Radio observations of gamma-ray burst (GRB) afterglows are essential for our understanding of the physics of relativistic blast waves, as they enable us to follow the evolution of GRB explosions much longer than the afterglows in any other wave band. We have performed a 3-year monitoring campaign of GRB 030329 with the Westerbork Synthesis Radio Telescopes and the Giant Metrewave Radio Telescope. Our observations, combined with observations at other wavelengths, have allowed us to determine the GRB blast wave physical parameters, such as the total burst energy and the ambient medium density, as well as to investigate the jet nature of the relativistic outflow. Further, by modelling the late-time radio light curve of GRB 030329, we predict that the Low-Frequency Array (30–240 MHz) will be able to observe afterglows of similar GRBs, and constrain the physics of the blast wave during its non-relativistic phase.
No supernovae detected in two long-duration gamma-ray bursts
Authors: Watson D , Fynbo J.P.U , Thöne C.C , Sollerman J
Published: February 2007

There is strong evidence that long-duration gamma-ray bursts (GRBs) are produced during the collapse of a massive star. In the standard version of the collapsar model, a broad-lined and luminous Type Ic core-collapse supernova (SN) accompanies the GRB. This association has been confirmed in observations of several nearby GRBs. Recent observations show that some long-duration GRBs are different. No SN emission accompanied the long-duration GRBs 060505 and 060614 down to limits fainter than any known Type Ic SN and hundreds of times fainter than the archetypal SN 1998bw that accompanied GRB 980425. Multi-band observations of the early afterglows, as well as spectroscopy of the host galaxies, exclude the possibility of significant dust obscuration. Furthermore, the bursts originated in star-forming galaxies, and in the case of GRB 060505, the burst was localized to a compact star-forming knot in a spiral arm of its host galaxy. We find that the properties of the host galaxies, the long duration of the bursts and, in the case of GRB 060505, the location of the burst within its host, all imply a massive stellar origin. The absence of an SN to such deep limits therefore suggests a new phenomenological type of massive stellar death.
Models for GRBs and diverse transients
Authors: Woosley S.E , Zhang Weiqun
Published: February 2007

The observational diversity of gamma-ray bursts (GRBs) has been increasing, and the natural inclination is a proliferation of models. We explore the possibility that at least part of this diversity is a consequence of a single basic model for the central engine operating in a massive star of variable mass, differential rotation rate and mass loss rate. Whatever that central engine may be—and here the collapsar is used as a reference point—it must be capable of generating both a narrowly collimated, highly relativistic jet to make the GRB and a wide angle, sub-relativistic outflow responsible for exploding the star and making the supernova bright. To some extent, the two components may vary independently; therefore, it is possible to produce a variety of jet energies and supernova luminosities. We explore, in particular, the production of low-energy bursts and find a lower limit of approximately 1048 erg s−1to the power required for a jet to escape a massive star before that star either explodes or is accreted. Lower energy bursts and ‘suffocated’ bursts may be particularly prevalent when the metallicity is high, i.e. in the modern universe at low red shift.
Culture in great apes: using intricate complexity in feeding skills to trace the evolutionary origin of human technical prowess
Authors: Byrne Richard W
Published: February 2007

Geographical cataloguing of traits, as used in human ethnography, has led to the description of ‘culture’ in some non-human great apes. Culture, in these terms, is detected as a pattern of local ignorance resulting from environmental constraints on knowledge transmission. However, in many cases, the geographical variations may alternatively be explained by ecology. Social transmission of information can reliably be identified in many other animal species, by experiment or distinctive patterns in distribution; but the excitement of detecting culture in great apes derives from the possibility of understanding the evolution of cumulative technological culture in humans. Given this interest, I argue that great ape research should concentrate on technically complex behaviour patterns that are ubiquitous within a local population; in these cases, a wholly non-social ontogeny is highly unlikely. From this perspective, cultural transmission has an important role in the elaborate feeding skills of all species of great ape, in conveying the ‘gist’ or organization of skills. In contrast, social learning is unlikely to be responsible for local stylistic differences, which are apt to reflect sensitive adaptations to ecology.
Cooperation and human cognition: the Vygotskian intelligence hypothesis
Authors: Moll Henrike , Tomasello Michael
Published: February 2007

Nicholas Humphrey's social intelligence hypothesis proposed that the major engine of primate cognitive evolution was social competition. Lev Vygotsky also emphasized the social dimension of intelligence, but he focused on human primates and cultural things such as collaboration, communication and teaching. A reasonable proposal is that primate cognition in general was driven mainly by social competition, but beyond that the unique aspects of human cognition were driven by, or even constituted by, social cooperation. In the present paper, we provide evidence for this Vygotskian intelligence hypothesis by comparing the social-cognitive skills of great apes with those of young human children in several domains of activity involving cooperation and communication with others. We argue, finally, that regular participation in cooperative, cultural interactions during ontogeny leads children to construct uniquely powerful forms of perspectival cognitive representation.
The genetic code is nearly optimal for allowing additional information within protein-coding sequences
Authors: Itzkovitz Shalev , Alon Uri
Published: February 2007

DNA sequences that code for proteins need to convey, in addition to the protein-coding information, several different signals at the same time. These “parallel codes” include binding sequences for regulatory and structural proteins, signals for splicing, and RNA secondary structure. Here, we show that the universal genetic code can efficiently carry arbitrary parallel codes much better than the vast majority of other possible genetic codes. This property is related to the identity of the stop codons. We find that the ability to support parallel codes is strongly tied to another useful property of the genetic code—minimization of the effects of frame-shift translation errors. Whereas many of the known regulatory codes reside in nontranslated regions of the genome, the present findings suggest that protein-coding regions can readily carry abundant additional information.
Stability of Plant Defense Proteins in the Gut of Insect Herbivores
Authors: Chen Hui , Gonzales-Vigil Eliana , Wilkerson Curtis G. , Howe Gregg A.
Published: February 2007

Plant defense against insect herbivores is mediated in part by enzymes that impair digestive processes in the insect gut. Little is known about the evolutionary origins of these enzymes, their distribution in the plant kingdom, or the mechanisms by which they act in the protease-rich environment of the animal digestive tract. One example of such an enzyme is threonine (Thr) deaminase (TD), which in tomato (Solanum lycopersicum) serves a dual role in isoleucine (Ile) biosynthesis in planta and Thr degradation in the insect midgut. Here, we report that tomato uses different TD isozymes to perform these functions. Whereas the constitutively expressed TD1 has a housekeeping role in Ile biosynthesis, expression of TD2 in leaves is activated by the jasmonate signaling pathway in response to herbivore attack. Ingestion of tomato foliage by specialist (Manduca sexta) and generalist (Trichoplusia ni) insect herbivores triggered proteolytic removal of TD2's C-terminal regulatory domain, resulting in an enzyme that degrades Thr without being inhibited through feedback by Ile. This processed form (pTD2) of TD2 accumulated to high levels in the insect midgut and feces (frass). Purified pTD2 exhibited biochemical properties that are consistent with a postingestive role in defense. Shotgun proteomic analysis of frass from tomato-reared M. sexta identified pTD2 as one of the most abundant proteins in the excrement. Among the other tomato proteins identified were several jasmonate-inducible proteins that have a known or proposed role in anti-insect defense. Subtilisin-like proteases and other pathogenesis-related proteins, as well as proteins of unknown function, were also cataloged. We conclude that proteomic analysis of frass from insect herbivores provides a robust experimental approach to identify hyperstable plant proteins that serve important roles in defense.
Regulation of Arbuscular Mycorrhization by Carbon. The Symbiotic Interaction Cannot Be Improved by Increased Carbon Availability Accomplished by Root-Specifically Enhanced Invertase Activity
Authors: Schaarschmidt Sara , González Mari-Cruz , Roitsch Thomas , Strack Dieter , Sonnewald Uwe , Hause Bettina
Published: February 2007

The mutualistic interaction in arbuscular mycorrhiza (AM) is characterized by an exchange of mineral nutrients and carbon. The major benefit of AM, which is the supply of phosphate to the plant, and the stimulation of mycorrhization by low phosphate fertilization has been well studied. However, less is known about the regulatory function of carbon availability on AM formation. Here the effect of enhanced levels of hexoses in the root, the main form of carbohydrate used by the fungus, on AM formation was analyzed. Modulation of the root carbohydrate status was performed by expressing genes encoding a yeast (Saccharomyces cerevisiae)-derived invertase, which was directed to different subcellular locations. Using tobacco (Nicotiana tabacum) alc∷cwINV plants, the yeast invertase was induced in the whole root system or in root parts. Despite increased hexose levels in these roots, we did not detect any effect on the colonization with Glomus intraradices analyzed by assessment of fungal structures and the level of fungus-specific palmitvaccenic acid, indicative for the fungal carbon supply, or the plant phosphate content. Roots of Medicago truncatula, transformed to express genes encoding an apoplast-, cytosol-, or vacuolar-located yeast-derived invertase, had increased hexose-to-sucrose ratios compared to β-glucuronidase-transformed roots. However, transformations with the invertase genes did not affect mycorrhization. These data suggest the carbohydrate supply in AM cannot be improved by root-specifically increased hexose levels, implying that under normal conditions sufficient carbon is available in mycorrhizal roots. In contrast, tobacco rolC∷ppa plants with defective phloem loading and tobacco pyk10∷InvInh plants with decreased acid invertase activity in roots exhibited a diminished mycorrhization.
Arabidopsis Vacuolar Sorting Mutants (green fluorescent seed) Can Be Identified Efficiently by Secretion of Vacuole-Targeted Green Fluorescent Protein in Their Seeds
Authors: Fuji Kentaro , Shimada Tomoo , Takahashi Hideyuki , Tamura Kentaro , Koumoto Yasuko , Utsumi Shigeru , Nishizawa Keito , Maruyama Nobuyuki , Hara-Nishimura Ikuko
Published: February 2007

Two Arabidopsis thaliana genes have been shown to function in vacuolar sorting of seed storage proteins: a vacuolar sorting receptor, VSR1/ATELP1, and a retromer component, MAIGO1 (MAG1)/VPS29. Here, we show an efficient and simple method for isolating vacuolar sorting mutants of Arabidopsis. The method was based on two findings in this study. First, VSR1 functioned as a sorting receptor for β-conglycinin by recognizing the vacuolar targeting signal. Second, when green fluorescent protein (GFP) fusion with the signal (GFP-CT24) was expressed in vsr1, mag1/vps29, and wild-type seeds, both vsr1and mag1/vps29 gave strongly fluorescent seeds but the wild type did not, suggesting that a defect in vacuolar sorting provided fluorescent seeds by the secretion of GFP-CT24 out of the cells. We mutagenized transformant seeds expressing GFP-CT24. From ∼3,000,000 lines of M2 seeds, we obtained >100 fluorescent seeds and designated them green fluorescent seed (gfs) mutants. We report 10 gfs mutants, all of which caused missorting of storage proteins. We mapped gfs1 to VSR1, gfs2 to KAM2/GRV2, gfs10 to the At4g35870 gene encoding a novel membrane protein, and the others to different loci. This method should provide valuable insights into the complex molecular mechanisms underlying vacuolar sorting of storage proteins.
Unique, Shared, and Redundant Roles for theArabidopsisSWI/SNF Chromatin Remodeling ATPases BRAHMA and SPLAYED
Authors: Bezhani Staver , Winter Cara , Hershman Steve , Wagner John D. , Kennedy John F. , Kwon Chang Seob , Pfluger Jennifer , Su Yanhui , Wagner Doris
Published: February 2007

Chromatin remodeling is emerging as a central mechanism for patterning and differentiation in multicellular eukaryotes. SWI/SNF chromatin remodeling ATPases are conserved in the animal and plant kingdom and regulate transcriptional programs in response to endogenous and exogenous cues. In contrast with their metazoan orthologs, null mutants in two Arabidopsis thaliana SWI/SNF ATPases, BRAHMA (BRM) and SPLAYED (SYD), are viable, facilitating investigation of their role in the organism. Previous analyses revealed that syd and brm null mutants exhibit both similar and distinct developmental defects, yet the functional relationship between the two closely related ATPases is not understood. Another central question is whether these proteins act as general or specific transcriptional regulators. Using global expression studies, double mutant analysis, and protein interaction assays, we find overlapping functions for the two SWI/SNF ATPases. This partial diversification may have allowed expansion of the SWI/SNF ATPase regulatory repertoire, while preserving essential ancestral functions. Moreover, only a small fraction of all genes depends on SYD or BRM for expression, indicating that these SWI/SNF ATPases exhibit remarkable regulatory specificity. Our studies provide a conceptual framework for understanding the role of SWI/SNF chromatin remodeling in regulation of Arabidopsis development.
A Conserved Carboxylesterase Is a SUPPRESSOR OF AVRBST-ELICITED RESISTANCE inArabidopsis
Authors: Cunnac Sébastien , Wilson Ariane , Nuwer Jamie , Kirik Angela , Baranage Gayathri , Mudgett Mary Beth
Published: February 2007

AvrBsT is a type III effector from Xanthomonas campestris pv vesicatoria that is translocated into plant cells during infection. AvrBsT is predicted to encode a Cys protease that targets intracellular host proteins. To dissect AvrBsT function and recognition in Arabidopsis thaliana, 71 ecotypes were screened to identify lines that elicit an AvrBsT-dependent hypersensitive response (HR) after Xanthomonas campestris pv campestris (Xcc) infection. The HR was observed only in the Pi-0 ecotype infected with Xcc strain 8004 expressing AvrBsT. To create a robust pathosystem to study AvrBsT immunity in Arabidopsis, the foliar pathogen Pseudomonas syringae pv tomato (Pst) strain DC3000 was engineered to translocate AvrBsT into Arabidopsis by the Pseudomonas type III secretion (T3S) system. Pi-0 leaves infected with Pst DC3000 expressing a Pst T3S signal fused to AvrBsT-HA (AvrBsTHYB-HA) elicited HR and limited pathogen growth, confirming that the HR leads to defense. Resistance in Pi-0 is caused by a recessive mutation predicted to inactivate a carboxylesterase known to hydrolyze lysophospholipids and acylated proteins in eukaryotes. Transgenic Pi-0 plants expressing the wild-type Columbia allele are susceptible to Pst DC3000 AvrBsTHYB-HA infection. Furthermore, wild-type recombinant protein cleaves synthetic p-nitrophenyl ester substrates in vitro. These data indicate that the carboxylesterase inhibits AvrBsT-triggered phenotypes in Arabidopsis. Here, we present the cloning and characterization of the SUPPRESSOR OF AVRBST-ELICITED RESISTANCE1.
Fracture of an Aluminosilicate Fiberboard
Authors: Olbert Blain H. , Schenck Steven R.
Published: February 2007

Mode‐I fracture of aluminosilicate fiberboard that is used in large mirror casting molds was studied. The material was idealized as a transversely isotropic, layered composite that was composed of planar sheets of crosslinked fibers. Elastic constants, the toughness (KR) curve, and the fracture work were measured at room temperature. The observed rising KR behavior was attributed to crack bridging. Experimental measurements of the bridging stress were made using a specimen‐renotching technique. Relationships between the bridging stress, KR, and fracture work were explored and shown to be consistent.
Grain Boundaries in Titania‐Doped α‐Alumina with Anisotropic Microstructure
Authors: Kebbede Anteneh , Messing Gary L. , Carim Altaf H.
Published: February 2007

The microstructure of sol‐gel‐derived alpha‐alumina (Al2O3) doped with 0.6 wt% titania, sintered at 1450°C for 1 h, consisted of thin platelets with (0001) faces in a matrix of equiaxed grains. Short facets at the edges of the platelets developed primarily parallel to the {102} planes, while some were parallel to the {113} planes; other edges showed irregular, curved boundaries. The basal surfaces of the platelets were coated with thin layers (0.5‐6 nm) of an amorphous titanium‐containing aluminosilicate phase, which also was present at triple points. No amorphous phase was found on the short faceted boundaries, on curved boundaries at platelet edges, or at grain boundaries of equiaxed, matrix grains. However, titanium enrichment was observed at all examined boundaries, suggesting that titanium segregation alone did not account for the development of anisotropic microstructure. Curved incursions on basal facets were associated with occasional particles of aluminum titanate (Al2TiO5).
In–Situ Transmission Electron Microscopy Crystallization Studies of Sol–Gel‐Derived Barium Titanate Thin Films
Authors: Gust Maria C. , Evans Neal D. , Momoda Leslie A. , Mecartney Martha L.
Published: February 2007

Barium titanate (BaTiO3) thin films that were derived from methoxypropoxide precursors were deposited onto (100) Si, Pt/Ti/SiO2/(100) Si, and molecular‐beam‐epitaxy‐grown (MBE‐grown) (100) BaTiO3 on (100) Si substrates by spin coating. The crystallization behavior of the amorphous‐gel films was characterized using in‐situ transmission electron microscopy heating experiments, glancing‐angle X‐ray diffraction, and differential thermal analysis/thermogravimetric analysis. Amorphous‐gel films crystallized at a temperature of ∼600°C to an intermediate nanoscale (5–10 nm) barium titanium carbonate phase, presumably BaTiO2CO3, that subsequently transformed to nanocrystalline (20–60 nm) BaTiO3. Random nucleation in the bulk of the gel film was observed on all substrates. In addition, oriented growth of BaTiO3 was concurrently observed on MBE‐grown BaTiO3 on (100) Si. High‐temperature decomposition of the intermediate carbonate phase contributed to nanometer‐scale residual porosity in the films. High concentrations of water of hydrolysis inhibited the formation of the intermediate carbonate phase; however, these sols precipitated and were not suitable for spin coating.
Size Effects in Barium Titanate Particles and Clusters
Authors: Li Xiaoping , Shih Wei‐Heng
Published: February 2007

Clustering has an important effect on the tetragonal‐cubic transformation of barium titanate (BaTiO3) particles. Small particles that would be cubic if they were by themselves can be tetragonal if they are in a cluster. The effects of clustering are shown in the behavior of the c/a ratio of the particles and the enthalpy change, ΔH, of transition as a function of particle size. The c/a ratio and the value of ΔH both decrease at a smaller particle size than those which are observed in samples where clustering is minimal. Our results are consistent with the observation that very small grains in polycrystalline samples can remain tetragonal even though the grain size is so small that it would be cubic if it were an individual particle. The transition temperature, TC, on the other hand, is insensitive to the particle size, which is similar to the observation in polycrystalline BaTiO3 that TC is insensitive to the grain size. The observed clustering effect is suggested to result from the reduction of depolarization energy of particles in clusters.
Synthesis of Highly Oriented Lithium Niobate Thin Film from Neutralized Aqueous Precursor Solution
Authors: Ono Satomi , Hirano Shin‐ichi
Published: February 2007

Lithium niobate thin films with a c‐axis orientation were synthesized from a neutralized aqueous precursor solution that was derived from lithium niobium double alkoxide. Lithium niobium hydroxide solution that was prepared by dissolving precipitates, through the complete hydrolysis of lithium niobium double alkoxide with water, was weakly basic. The hydroxide solution was neutralized with acetic acid to give neutralized homogeneous lithium niobium hydroxide solution. The film that was prepared at 500°C from the neutralized precursor solution had a smooth surface texture without cracks and pores. A pole‐figure pattern indicated that the crystalline film was twinned, with rotation by 60° oriented along the c‐axis.
Development of an Equivalent Circuit Model for Cement Pastes from Microstructural Considerations
Authors: Macphee Donald E. , Sinclair Derek C. , Cormack Sarah L.
Published: February 2007

The general approach to equivalent circuit modeling of cement pastes has been to interpret spectra obtained from ac impedance measurements, assigning electrical responses to microstructural features such as hydration products and fluid‐filled porosity. In this paper, we take an alternative approach. Starting with a consideration of paste microstructures and the potential conduction pathways that such microstructures could support, we propose an equivalent circuit model. Ac impedance data from pore‐reduced cements have been measured for the first time and are used to test the model. This approach has permitted estimation of conductivities of in situ pore fluid, which we believe to be influenced by hydrogen bonding to varying extents depending on pore size, and hydration product. Preliminary results are in broad agreement with data obtained by alternative methods.
Forming Single‐Phase Laminates via the Gelcasting Technique
Authors: Baskin Donald M. , Zimmerman Michael H. , Faber K. T. , Fuller Edwin R.
Published: February 2007

Single–phase laminates of iron titanate were formed by gelcasting in both the presence and absence of a magnetic field to produce alternating layers of textured and nontextured microstructure, respectively. X–ray analysis was performed on each lamina verifying that alignment was maintained throughout processing. Tunnel cracks were found in trilayer laminates (nontextured/textured/nontextured) when the alignment direction was parallel to the interface between layers. The cracks are consistent with a stress profile of residual tension parallel to the interface in the textured layer.
Microwave Characteristics of (Pb,Ca)(Fe,Nb,Sn)O3 Dielectric Materials
Authors: Kucheiko Sergey , Choi Ji‐Won , Kim Hyun‐Jai , Yoon Seok‐Jin , Jung Hyung‐Jin
Published: February 2007

The dielectric properties of (Pb1−xCax){(Fe1/2Nb1/2)1–ySny}O3 solid solutions, where 0.4 lessthan equal tox ≤ 0.6, y = 0.05, 0.1, have been investigated at microwave frequencies. The replacement of Fe3+/Nb5+ by Sn4+ at the B–site of the perov‐skite structure considerably improves the loss quality factor Q and does not remarkably affect the dielectric constant epsilonr and the temperature coefficient of resonant frequency tauf. The tauf value of nearly 0 ppm/°C can be realized for x= 0.55. New high‐quality dielectric ceramics having epsilonr of 85.3‐89.9,Qf values of 7510‐8600 GHz, and τf of 0‐9 ppm/°C were obtained at 1150°C for 3 h sintering in air. The influence of the sintering atmosphere on dielectric properties was also investigated.
Evaluation of Microstructure Characteristics of Lithium Niobate Single‐Crystal Fiber with Magnesium‐Ion‐Indiffused Cladding
Authors: Que Wenxiu , Lim Siakpiang , Zhang Liangying , Yao Xi
Published: February 2007

A magnesium ion indiffusion process is applied to lithium niobate single–crystal fibers. Electron probe microanalysis shows that magnesium ions have diffused into the bulk of the crystal fibers and the magnesium ion concentration in the magnesium–diffused layer has an approximately parabolic profile, which corresponds to that of theoretical simulation. It is shown by conventional X–ray diffraction and scanning electron microscopy that a good starting single crystal of the magnesium–diffused crystal fiber can be preserved by controlling suitable diffusion parameters such as diffusion temperature, diffusion time, and MgO film thickness, etc., to ensure the completeness of magnesium ion indiffusion, but the magnesium–diffused region etches differently from virgin‐region crystals.
Processing and Electromechanical Properties of (Bi0.5Na0.5)(1−1.5x)LaxTiO3Ceramics
Authors: Herabut Aree , Safari Ahmad
Published: February 2007

Bismuth sodium titanate (Bi0.5Na0.5TiO3, BNT) with 0–6 at.% lanthanum was prepared by the conventional mixed oxide method. Each composition was calcined at 800–900°C for 2–5 h to form a pure perovskite phase. Green pellets were sintered at 1050–1150°C for 1–4 h to obtain dense ceramics with at least 95% of theoretical density. X–ray diffraction (XRD) showed phase distortion as lanthanum was added to this system. Meanwhile, a small amount of La was found to affect the grain size and had an influence on the poling conditions and electrical properties. The BNT–based composition with 1 at.% La doping provided a dielectric constant (K) of 560, a piezoelectric charge constant (d33) of 92 pC/N, and a hydrostatic piezoelectric coefficient (dh) of 72 pC/N.
Synthesis of Porous Silicon Nitride with Unidirectionally Aligned Channels Using Freeze‐Drying Process
Authors: Fukasawa Takayuki , Deng Zhen‐Yan , Ando Motohide , Ohji Tatsuki , Kanzaki Shuzo
Published: February 2007

Porous silicon nitride with macroscopically aligned channels was synthesized using a freeze‐drying process. Freezing of a water‐based slurry of silicon nitride was done while unidirectionally controlling the growth direction of the ice. Pores were generated subsequently by sublimation of the columnar ice during freeze‐drying. By sintering this green body, a porous silicon nitride with high porosity (over 50%) was obtained and its porosity was controllable by the slurry concentration. The porous Si3N4 had a unique microstructure, where macroscopically aligned open pores contained fibrous grains protruding from the internal walls of the Si3N4 matrix. It is hypothesized that vapor/solid phase reactions were important to the formation mechanism of the fibrous grains.
Topotatic‐Like Phase Transformation of Amorphous Lead Titanate to Cubic Lead Titanate
Authors: Leite Edson R. , Paris Elaine C. , Longo Elson , Jr. Lanciotti Francesco , Campos Carlos E. M. , Pizani Paulo S. , Mastellaro Valmor , Paskocimas Carlos A. , Varela Jose Arana
Published: February 2007

The crystallization process of lead titanate (PT) prepared using the polymeric precursor method was investigated using X‐ray diffractometry, Raman spectroscopy, electron microscopy, and X‐ray absorption spectroscopy techniques. The results showed that amorphous PT was formed by an O–Ti–O structure composed of fivefold and sixfold oxygen‐coordinated titanium. The local structure of the amorphous PT phase was similar to that of the cubic PT phase, i.e., similar coordination number and similar bond lengths, leading to a topotactic‐like transformation during the phase transformation from amorphous to cubic perovskite PT. Because of the low crystallization temperature, every transformation observed during the crystallization process was associated with a short‐range rearrangement process.
Highly Reactive β‐Dicalcium Silicate
Authors: Singh Nakshatra B. , Rai Sarita , Singh Neelam
Published: February 2007

Calcium silicate hydrate was prepared by hydrothermal reaction between calcium oxide and silica (C/S = 2.0) at a temperature of 205°–215°C and a pressure of 17–19 bar. This reaction with decomposition at 900°C produced highly reactive β‐dicalcium silicate (specific surface area 4.55 m2/g) contaminated with small amounts of wollastonite as an impurity. Infrared spectral studies have shown that β‐dicalcium silicate prepared at 900°C is less symmetric compared with the control prepared at 1450°C using boron trioxide as a stabilizer. The specific surface area of β‐dicalcium silicate decreased with temperature. The hydration studies were done by determining the nonevaporable water, calcium hydroxide (CH) contents, and specific surface area of the hydrated samples. X‐ray diffraction studies were also done. The results showed that prepared β‐dicalcium silicate is highly reactive. Calcium chloride (1.0 wt%) and gypsum retard the hydration. Possible causes of high reactivity have been discussed.
Conversion Process of Strontium–Titanium Bimetallic Methoxyethoxide Precursor into SrTiO3 via Hydrolysis/Calcination
Authors: Okayama Junko , Takaya Itaru , Nashimoto Keiichi , Sugahara Yoshiyuki
Published: February 2007

The conversion of a Sr–Ti bimetallic methoxyethoxide precursor into SrTiO3 via hydrolysis and/or calcination was investigated. Hydrolysis with various water/metal molar ratios (rH; rH= 0.5, 2, 4, 6, 8, 10) in tetrahydrofuran at reflux resulted in a decrease in the amount of the methoxyethoxyl groups, and the hydrolyzed products were soluble with rH≤ 2. At rH≥ 8, SrTiO3 was crystallized without calcination. Both the hydrolyzed and unhydrolyzed precursors (rH= 0, 0.5, 2) were calcined in dry air at 550°–800°C. SrTiO3 was crystallized on calcination at ≥550°C from amorphous materials with a considerable loss of carbon, which was present as both chars and carbonate ions.
Effect of Dilution and Porosity on Self‐Propagating High‐Temperature Synthesis of Silicon Nitride
Authors: Cano Irene G. , Borovinskaya Inna P. , Rodriguez Miguel A. , Grachev Vladimir V.
Published: February 2007

Self‐propagating high‐temperature synthesis is a very easy and low‐cost method to synthesize Si3N4. The nitriding of silicon powder takes place in a self‐sustained regime under high pressures of nitrogen with dilution of silicon by Si3N4. In this work effects of dilution and green‐mixture porosity on combustion velocity and phase content of reaction products are studied. Results are compared with previous work of other authors and different behaviors are found. An explanation of these behaviors is given.
Synthesis and Magneto‐mechanical Properties of Ce‐TZP/La M‐Type Hexaferrite Composite
Authors: Kojima Takashi , Sakamoto Wataru , Yogo Toshinobu , Fujii Takashi , Hirano Shin‐ichi
Published: February 2007

An in situ composite composed of ceria‐stabilized tetragonal zirconia polycrystals (Ce‐TZP) and La{Co0.5Fe0.5(Fe0.9Al0.1)11}O19 was synthesized from a powder mixture of Ce‐TZP, La(Fe0.9Al0.1)O3, Fe2O3, Al2O3, and CoO. The dense Ce‐TZP dispersed with platelike La{Co0.5Fe0.5(Fe0.9Al0.1)11}O19 crystals as a second phase were formed after sintering from 1250° to 1350°C. The saturation magnetization of the insitu composite Ce‐TZP/La{Co0.5Fe0.5(Fe0.9Al0.1)11}O19 was proportional to the mass fraction of the hexaferrite second phase in Ce‐TZP. The coercivity of the composite with a 20 mass% of second phase decreased from 9.14 to 2.52 kOe (from 728 to 201 kA/m) after the pulverization of the composite. The susceptibility (χ) increased by 15%–25% under uniaxial stress on the composite. The change of the susceptibility (Δχ/χ) value increased with decreasing the mass fraction of the second phase in the composite. The Δχ was found to increase linearly with applied stress and abruptly change on cracking, which is expected for the application in fracture sensing of the composite.
New Route for the Extraction of Crude Zirconia from Zircon
Authors: Welham Nicholas J.
Published: February 2007

A commercial grade of zircon (ZrSiO4) concentrate was mechanically milled with MgO for up to 100 h in a laboratory‐scale mill. The resultant powders were subjected to thermal processing, chemical leaching, and X‐ray diffraction (XRD). There was no direct evidence of reaction during the milling step, with no new phases evident from XRD. Leaching of the powder showed that a reaction had occurred, and increased solubility with milling time was attributed to the formation of a nanostructured Mg‐Zr‐Si oxide, which dissolved congruently. Heating the powders resulted in a number of thermal events, including the formation/crystallization of ZrO2 and Mg2SiO4. Thermal treatment of the milled powders allowed selective chemical leaching of the magnesium and silicon, leaving a powder containing ∼90% ZrO2.
Electrical Conductivities of (CeO2)1−x(Y2O3)x Thin Films
Authors: Tian Chunyan , Chan Siu‐Wai
Published: February 2007

Electrical properties of CeO2 thin films of different Y2O3 dopant concentration as prepared earlier were studied using impedance spectroscopy. The ionic conductivities of the films were found to be dominated by grain boundaries of high conductivity as compared with that of the bulk ceramic of the same dopant concentration sintered at 1500°C. The film grain‐boundary conductivities were investigated with regard to grain size, grain‐boundary impurity segregation, space charge at grain boundaries, and grain‐boundary microstructures. Because of the large grain boundary and surface area in thin films, the impurity concentration is insufficient to form a continuous highly resistive Si‐rich glassy phase at grain boundaries, such that the resistivity associated with space‐charge layers becomes important. The grain‐boundary resistance may originate from oxygen‐vacancy‐trapping near grain boundaries from space‐charge layers. High‐resolution transmission electron microscopy coupled with a trans‐boundary profile of electron energy loss spectroscopy gives strong credence to the space‐charged layers. Since the conductivities of the films were observed to be independent of crystallographic texture, the interface misorientation contribution to the grain‐boundary resistance is considered to be negligible with respect to those of the impurity layer and space‐charge layers.
Dopant Effect on Local Dielectric Properties in Barium Titanate Based Electroceramics Determined by Transmission EELS
Authors: Katti Kalpana S. , Qian Maoxu , Dogan Fatih , Sarikaya Mehmet
Published: February 2007

Local electronic excitations of Nb‐doped BaTiO3 electroceramic were investigated using low‐loss electron energy loss (EEL) spectroscopy with a transmission electron microscope. The variations in electronic structure of the BaTiO3 were monitored as a function of Nb content by using Kramers‐Krönig analysis of the low‐loss EEL spectra. We found that the valence state of Nb (+5) as compared with that of the Ti (+4) introduces changes in the valence and conduction band states of BaTi1−xNbxO3 samples. The real part of the dielectric function, Re(1/ɛ), displays an increasingly less negative character with higher amounts of dopant and the valence plasmon exhibits “quasi‐plasmon” characteristics with the addition of Nb (at 0.0–1.8 at.%). Further, the plasmon energy shifts (by about 0.5 eV) to higher values with Nb additions. Significant changes take place in oscillator strengths of excitations in local (nanometer‐scale) regions of the perovskite samples. This investigation demonstrates a method to quantitatively assess electronic properties, at the submicrometer scale, of doped ceramics used in electronic and electrooptical applications.
Grain Boundary Diffusion of Magnesium in Zirconia
Authors: Bak Tadeusz , Nowotny Janusz , Prince Kathryn , Rekas Mieczyslaw , Sorrell Charles C.
Published: February 2007

This paper reports the transport kinetics of Mg in cubic yttria‐stabilized zirconia (containing 10% mol of Y2O3 (10YSZ)) involving the bulk and the grain boundary diffusion coefficients. The diffusion‐controlled concentration profiles of Mg were determined using secondary ion mass spectrometry (SIMS) in the range 1073–1273 K. The determined bulk diffusion coefficient and the grain boundary diffusion product may be expressed as the following functions of temperature, respectively: D= 5.7 exp[(−390 kJ/mol)/RT] cm2·s−1 and D′αδ= 3.2 × 10−15 exp[(−121 kJ/mol)/RT] cm3·s−1, where α is the segregation enrichment factor and δ is the boundary layer thickness. The grain boundary enhancement factor decreases with temperature from 105 at 1073 K to 103 at 1273 K.
Controlled Precracking of Fracture Mechanics Specimens Using Contact Stresses
Authors: Hashimoto Atsushi , Kovar Desiderio
Published: February 2007

A simple method is proposed for introducing precracks into thin‐plate fracture mechanics specimens, i.e., compact‐tension and double‐cantilever‐beam specimens, using standard testing equipment and without performing complicated machining operations on the specimens. The surface of the specimen is first scored to a known length, using a scribe, and the specimen is then compressed between polymer blocks. Mismatch between the elastic properties of the polymer and the specimen results in an in‐plane tensile stress in the vicinity of the scratch that causes a crack to initiate from the scratch and propagate through the specimen thickness. Provided that certain conditions are met, the crack arrests without significant growth beyond the initial scratch length. The result is a straight, through‐thickness precrack of controllable length. Fracture toughness measurements made on glass specimens precracked using the proposed method are in good agreement with literature values for this material.
Thermogravimetry, Differential Thermal Analysis, and Mass Spectrometry Study of the Silicon Nitride–Boron Carbide–Carbon Reaction System for the Synthesis of Silicon Carbide–Boron Nitride Composites
Authors: Zhang Guo‐Jun , Yang Jian‐Feng , Ohji Tatsuki
Published: February 2007

Thermogravimetry, differential thermal analysis, mass spectrometry, and X‐ray diffractometry were used to study the reaction process of the in situ reaction between Si3N4, B4C, and carbon for the synthesis of silicon carbide–boron nitride composites. Atmospheres with a low partial pressure of nitrogen (for example argon + 5%–10% nitrogen) seemed to inhibit denitrification and also maintain a high reaction rate. However, the reaction rate decreased significantly in a pure nitrogen atmosphere. The experimental mass spectrometry results also revealed that B4C in the Si3N4–B4C–C system inhibited the reaction between Si3N4 and carbon and, even, the decomposition of Si3N4. The present results indicate that boron could be a composition stabilizer for ceramic materials in the Si‐N‐C system used at high temperature.
Intrinsic Reaction and Self‐Diffusion Kinetics for Silicon Carbide Synthesis by Rapid Carbothermal Reduction
Authors: Johnson Jacob A. , Hrenya Christine M. , Weimer Alan W.
Published: February 2007

A one‐dimensional nonisothermal model has been developed for the “rapid carbothermal reduction” synthesis of fine silicon carbide powders. Intrinsic reaction and self‐diffusion kinetics are identified through simulation of the model and comparison to experimental results. The reaction rate follows a shrinking‐core mechanism and is described by the relation [formula omitted] The self‐diffusion coefficient for SiC in the aerosol flow reactor is described by the relation
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The self‐diffusion coefficient for SiC in the aerosol flow reactor is described by the relation

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Oxidation Behavior of Liquid‐Phase Sintered Silicon Carbide with Aluminum Nitride and Rare‐Earth Oxides (Re2O3, where Re = Y, Er, Yb)
Authors: Choi Heon‐Jin , Lee June‐Gunn , Kim Young‐Wook
Published: February 2007

Silicon carbide (SiC) ceramics have been fabricated by hot‐pressing and subsequent annealing under pressure with aluminum nitride (AlN) and rare‐earth oxides (Y2O3, Er2O3, and Yb2O3) as sintering additives. The oxidation behavior of the SiC ceramics in air was characterized and compared with that of the SiC ceramics with yttrium–aluminum–garnet (YAG) and Al2O3–Y2O3–CaO (AYC). All SiC ceramics investigated herein showed a parabolic weight gain with oxidation time at 1400°C. The SiC ceramics sintered with AlN and rare‐earth oxides showed superior oxidation resistance to those with YAG and Al2O3–Y2O3–CaO. SiC ceramics with AlN and Yb2O3 showed the best oxidation resistance of 0.4748 mg/cm2 after oxidation at 1400°C for 192 h. The minimization of aluminum in the sintering additives was postulated as the prime factor contributing to the superior oxidation resistance of the resulting ceramics. A small cationic radius of rare‐earth oxides, dissolution of nitrogen to the intergranular glassy film, and formation of disilicate crystalline phase as an oxidation product could also contribute to the superior oxidation resistance.