bluuebunny/crossref_metadata_2025 huggingface dataset:
Foxp3+CD25–CD4 T cells constitute a reservoir of committed regulatory cells that regain CD25 expression upon homeostatic expansion
Authors: Zelenay Santiago , Lopes-Carvalho Thiago , Caramalho Iris , Moraes-Fontes Maria Francisca , Rebelo Manuel , Demengeot Jocelyne
Published: March 2005

Expression of the IL-2 receptor α chain (CD25) by peripheral CD4 T cells follows cellular activation. However, CD25 expression by CD4 cells is widely used as a marker to identify regulatory T cells (TR), although cells with regulatory properties are also found in the CD4+CD25–subset. By usingin vivofunctional assays and Foxp3 expression as a faithful marker of TRdifferentiation, we have evaluated the requirements for CD25 expression by peripheral TR. We first show thatin vivodepletion of CD25+cells prevents the development of spontaneous encephalomyelitis in recombination-activating gene (RAG)-deficient anti-myelin basic protein T cell antigen receptor (TCR) transgenic mice, and allows disease induction in otherwise healthy RAG-competent transgenic mice. Similar treatment in normal thymectomized animals is followed by the fast recovery of a normal number of CD25+TR. Consistently, Foxp3-expressing TRencompassed in the CD25–cell population convert to CD25+after homeostatic expansion and are selectable by IL-2in vitro. Surface expression of CD25 on TRis controlled by the activity of conventional CD4 cells and is fully labile because it can be lost and regained without affecting the functional potential of the cells. These findings reveal that Foxp3-expressing CD25–cells constitute a peripheral reservoir of differentiated TR, recruited to the CD25+pool upon homeostatic expansion and/or activation. This analysis, together with the notion that physiological commitment of TRtakes place exclusively in the thymus should help for the interpretation of experiments assessing peripheral TRdifferentiation from naive CD4 T cells, defined as CD25–.
Calling for help is independently modulated by brain systems underlying goal-directed behavior and threat perception
Authors: Fox Andrew S. , Oakes Terrence R. , Shelton Steven E. , Converse Alexander K. , Davidson Richard J. , Kalin Ned H.
Published: March 2005

In primates, during times of need, calling for help is a universal experience. Calling for help recruits social support and promotes survival. However, calling for help also can attract predators, and it is adaptive to inhibit calls for help when a potential threat is perceived. Based on this, we hypothesized that individual differences in calling for help would be related to the activity of brain systems that mediate goal-directed behavior and the detection of threat. By using high-resolution positron emission tomography in rhesus monkeys undergoing social separation, we demonstrate that increased [
18
F]-fluoro-2-deoxy-
d
-glucose uptake in the right dorsolateral prefrontal cortex and decreased uptake in the amygdala independently predict individual differences in calling for help. When taken together, these two regions account for 76% of the variance in calling for help. This result suggests that the drive for affiliation and the perception of threat determine the intensity of an individual's behavior during separation. These findings in monkeys are relevant to humans and provide a conceptual neural framework to understand individual differences in how primates behave when in need of social support.
Phytoplankton species richness scales consistently from laboratory microcosms to the world's oceans
Authors: Smith Val H. , Foster Bryan L. , Grover James P. , Holt Robert D. , Leibold Mathew A. , deNoyelles Frank
Published: March 2005

Species-area relationships have been observed for virtually all major groups of macroorganisms that have been studied to date but have not been explored for microscopic phytoplankton algae, which are the dominant producers in many freshwater and marine ecosystems. Our analyses of data from 142 different natural ponds, lakes, and oceans and 239 experimental ecosystems reveal a strong species-area relationship with an exponent that is invariant across ecosystems that span >15 orders of magnitude in spatial extent. A striking result is that the species-area relationship derived from small-scale experimental studies correctly scales up to natural aquatic ecosystems. These results significantly broaden our knowledge of the effects of island size on biodiversity and also confirm the relevance of experimentally derived data to the analysis and understanding of larger-scale ecological patterns. In addition, they confirm that patterns in microbial diversity are strongly consistent with those that have been repeatedly reported in the literature for macroorganisms.
Architecture of recombination intermediates visualized by in-gel FRET of λ integrase–Holliday junction–arm DNA complexes
Authors: Radman-Livaja Marta , Biswas Tapan , Mierke Dale , Landy Arthur
Published: March 2005

λ Integrase (Int) mediates recombination between attachment sites on phage and
Escherichia coli
DNA. Int is assisted by accessory protein-induced DNA loops in bridging pairs of distinct “arm-type” and “core-type” DNA sites to form synapsed recombination complexes that subsequently recombine by means of a Holliday junction (HJ) intermediate. An in-gel FRET assay was developed and used to measure 15 distances between six points in two Int–HJ complexes containing arm-DNA oligonucleotides, and 3D maps of these complexes were derived by distance-geometry calculations. The maps reveal unexpected positions for the arm-type DNAs relative to core sites on the HJ and a new Int conformation in the HJ tetramer. The results show how the position of arm DNAs determines the bias of catalytic activities responsible for directional resolution, provide insights into the organization of Int higher-order complexes, and lead to models of the structure of the full HJ recombination intermediates.
Lifelong elimination of hyperbilirubinemia in the Gunn rat with a single injection of helper-dependent adenoviral vector
Authors: Toietta Gabriele , Mane Viraj P. , Norona Wilma S. , Finegold Milton J. , Ng Philip , McDonagh Antony F. , Beaudet Arthur L. , Lee Brendan
Published: March 2005

Crigler–Najjar syndrome is a recessively inherited disorder characterized by severe unconjugated hyperbilirubinemia caused by a deficiency of uridine diphospho-glucuronosyl transferase 1A1. Current therapy relies on phototherapy to prevent kernicterus, but liver transplantation presently is the only permanent cure. Gene therapy is a potential alternative, and recent work has shown that helper-dependent adenoviral (HD-Ad) vectors, devoid of all viral coding sequences, induce prolonged transgene expression and exhibit significantly less chronic toxicity than early-generation Ad vectors. We used a HD-Ad vector to achieve liver-restricted expression of human uridine diphospho-glucuronosyl transferase 1A1 in the Gunn rat, a model of the human disorder. Total plasma bilirubin levels were reduced from >5.0 mg/dl to «1.4 mg/dl for >2 yr after a single i.v. administration of vector expressing the therapeutic transgene at a dose of 3 × 10
12
viral particles per kg. HPLC analysis of bile from treated rats showed the presence of bilirubin glucuronides at normal WT levels >2 yr after one injection of vector, and i.v. injection of bilirubins IIIα and XIIIα in the same animals revealed excess bilirubin-conjugating capacity. There was no significant elevation of liver enzymes (alanine aminotransferase) and only transient, moderate thrombocytopenia after injection of the vector. A clinically significant reduction in serum bilirubin was observed with a dose as low as 6 × 10
11
viral particles per kg. We conclude that complete, long-term correction of hyperbilirubinemia in the Gunn rat model of Crigler–Najjar syndrome can be achieved with one injection of HD-Ad vector and negligible chronic toxicity.
Role of structural determinants in folding of the sandwich-like proteinPseudomonas aeruginosaazurin
Authors: Wilson Corey J. , Wittung-Stafshede Pernilla
Published: March 2005

An invariant substructure that forms two interlocked pairs of neighboring β-strands occurs in essentially all known sandwich-like proteins. Eight conserved positions in these strands were recently shown to act as structural determinants. To test whether the residues at these invariant positions are conserved for mechanistic (i.e., part of folding nucleus) or energetic (i.e., governing native-state stability) reasons, we characterized the folding behavior of eight point-mutated variants of the sandwich-like proteinPseudomonas aeruginosaapo-azurin. We find a simple relationship among the conserved positions: half of the residues form native-like interactions in the folding transition state, whereas the others do not participate in the folding nucleus but govern high native-state stability. Thus, evolutionary preservation of these specific positions gives both mechanistic and energetic advantages to members of the sandwich-like protein family.
A role for the anaphase-promoting complex inhibitor Emi2/XErp1, a homolog of early mitotic inhibitor 1, in cytostatic factor arrest of
Xenopus
eggs
Authors: Tung Jeffrey J. , Hansen David V. , Ban Kenneth H. , Loktev Alexander V. , Summers Matthew K. , Adler John R. , Jackson Peter K.
Published: March 2005

Unfertilized vertebrate eggs are arrested in metaphase of meiosis II with high cyclin B/Cdc2 activity to prevent parthenogenesis. Until fertilization, exit from metaphase is blocked by an activity called cytostatic factor (CSF), which stabilizes cyclin B by inhibiting the anaphase-promoting complex (APC) ubiquitin ligase. The APC inhibitor early mitotic inhibitor 1 (Emi1) was recently found to be required for maintenance of CSF arrest. We show here that exogenous Emi1 is unstable in CSF-arrested
Xenopus
eggs and is destroyed by the SCF
βTrCP
ubiquitin ligase, suggesting that endogenous Emi1, an apparent 44-kDa protein, requires a stabilizing factor. However, anti-Emi1 antibodies crossreact with native Emi2/Erp1/FBXO43, a homolog of Emi1 and conserved APC inhibitor. Emi2 is stable in CSF-arrested eggs, is sufficient to prevent CSF release, and is rapidly degraded in a Polo-like kinase 1-dependent manner in response to calcium-mediated egg activation. These results identify Emi2 as a candidate CSF maintenance protein.
Agrarian Vista or Vortex: African rural livelihood policies
Authors: Bryceson Deborah Fahy
Published: March 2005

This article explores the concepts of livelihoods, sustainability and poverty alleviation with reference to recent rural economy survey findings in subSaharan Africa, policies in the international development policy arena during the last 20 years, and South Africa's rural history. It is argued that processes of deagrarianisation and depeasantisation have accelerated in association with the implementation of structural adjustment policies. Village case-study evidence from various African countries indicates a decline in peasant commodity production, a surge in non-agricultural income diversification, the proliferation of multi-occupational households, accelerating rural class stratification and growing poverty (‘non-agricultural’ activities are those that do not directly involve plant or animal husbandry). International financial institutions, specifically the World Bank, have become increasingly alert to rural poverty over the last few years but tend to ignore their policy influence in this field. The sustainable rural livelihoods approach acknowledges structural change in rural areas but has not yet fully analysed the depth of ongoing change and the policy scope needed to deflect rural poverty. A schematic look at deagrarianisation in South Africa and the effect of past and present policy interventions in South African rural areas illustrates the potential continental dimensions of agricultural labour displacement.
Elicited and spontaneous communicative functions and stability of conversational measures with children who have pragmatic language impairments
Authors: Adams Catherine , Lloyd Julian
Published: March 2005

Background: The preliminary phase of a project aimed at establishing appropriate outcome measures for intervention with children who have pragmatic language impairments (PLI) is reported. Assessment methods for children with PLI are considered in the context of developing outcome measures for intervention studies. Communicative function assessments in elicitation and conversational contexts are compared. The stability of measures derived from conversational profiling is also considered.

Aims: To investigate the utility of an elicited communicative function assessment in discriminating the pragmatic characteristics of children with PLI and to compare this method to conversational profiling. An additional aim was to estimate the degree of variation on conversational indices derived from interactions with children with PLI.

Methods & Procedures: Fifteen children with PLI (mean age 9;5 years) and an age‐matched control group were assessed on two occasions on a new communicative function elicitation task and on a conversation task. A checklist of communicative functions was employed in analysing the elicitation and the conversation tasks. An analysis of conversation was carried out to derive conversational indices such as verbosity and meshing.

Outcomes & Results: The elicitation task failed to discriminate between the PLI and control groups and showed a strong ceiling effect. Significant between‐group differences were found for both communicative function in conversation measures and on conversational indices. The variation in conversation indices is relatively small compared with the baseline measures.

Conclusions: A more representative picture of communicative function ability arises from unstructured tasks rather than from structured elicitation tasks for the age group of children with PLI. The elicitation procedure outlined in this paper might be better suited to a younger age group. Differences between communicative function performance on elicitation and conversation situations suggest a strong effect of context on the pragmatic performance of children with PLI. The conversational indices reported show sufficient stability to be employed in an outcome measure provided the minor variations indicated are factored into estimates of change.
Personal photon dosemeter trial—Devonport Royal Dockyard
Authors: Collison Roger
Published: March 2005

To establish an understanding of the operational responses of various personal dosemeters employed at Devonport and to assess new types of dosemeters, a photon dosemeter trial was conducted. Most day-to-day exposure is to relatively low dose rates. Therefore the suitability of each dosemeter for use within the relatively low Devonport dose rate environment has been assessed.

The Panasonic TLD demonstrated a good representation of the dose within the medium to higher gamma energy ranges with an unexpected under-response at lower energies.

The optically stimulated luminescent dosemeter showed a varied response within a degraded60Co environment.

With consistent under-response, the NRPB TLD and film badge were found to generally be unsuitable for sites such as Devonport.

The Harshaw TLD demonstrated a good representation of the dose.

The RADOS RAD80 and QFD fail to meet current best industry standards. However, the QFD is the only direct reading dosemeter suitable for use where intrinsically safe equipment is required.

The RADOS RAD52 and SAIC PD 2i show a reasonable representation of the dose received but should be adjusted to read within an operational60Co environment.

Direct ion storage and Thermos electronic personal dosemeters showed good representations of the dose. Inherent characteristics combined with the associated systems led to the conclusion that these dosemeters should be employed for preference.
A parasite-mediated life-history shift in
Daphnia magna
Authors: Chadwick William , Little Tom J
Published: March 2005

The impact of parasitism on host populations will be modulated by both genetic variation for susceptibility, and phenotypically plastic life-history traits that are altered to lessen the fitness consequences of infection. In this study we tested for life-history shifts in the crustacean
Daphnia magna
following exposure to the horizontally transmitted microsporidian,
Glugoides intestinalis
. In two separate experiments, we exposed hosts to parasite spores and measured their fecundity relative to controls. We show that hosts exposed to
G. intestinalis
show fecundity compensation, i.e. hosts shift their life-history strategy towards early reproduction. Our experiments included multiple host genotypes, and subtle differences among them indicated that fecundity compensation could be subject to parasite-mediated natural selection.
Lymphangioma‐like Kaposi sarcoma
Authors: Ramirez James A. , Laskin William B. , Guitart Joan
Published: March 2005

Background:  Lymphangioma‐like Kaposi's sarcoma (LLKS) is a rare morphologic expression of Kaposi's sarcoma (KS) that occurs in virtually all of the well‐recognized clinical subtypes of the disease and has the potential to mimic other pathologic processes. In this study, we present the clinical and pathological features of four patients with LLKS.

Methods:  Four cases of LLKS were retrieved from the dermatopathology files of our institution. All four tumours were tested immunohistochemically with anti‐human herpesvirus‐8 (HHV‐8) latent nuclear antigen‐1 (LNA‐1) and anti‐CD34 antibodies.

Results:  Clinically, each patient presented with violaceous patches, papules or plaques; one patient presented with bullous lesions. All of the LLKS biopsy specimens revealed areas with characteristic light microscopic features of KS. Lymphangioma‐like foci consisted of ectatic, irregularly shaped vascular spaces lined by mildly atypical endothelial cells. All tumour cells, including those associated with LLKS foci, showed a strong and diffuse reactivity for anti‐HHV‐8 LNA‐1 and anti‐CD34. KS progressed slowly in two patients with adequate follow‐up.

Conclusions:  As LLKS can mimic other disease processes, the correct diagnosis relies heavily on the recognition of salient clinical and histological features of conventional KS, including a strong immunohistochemical expression of HHV‐8‐associated LNA‐1 in lesional cells.
Liquid Redistribution during Liquid‐Phase Sintering
Authors: SHAW T.M.
Published: March 2005

A simple two‐dimensional packing model, consisting of arrays of circular particles, was used to calculate the free energy changes associated with the filling of pores of different coordinations with liquid. The calculations were used to determine the equilibrium distributions of a liquid in different packing arrangements of particles. The effect of both the volume fraction of liquid and shrinkage on liquid distribution was examined. It was found that, when liquid redistribution can easily take place, the volume fraction of liquid phase, the pore size distribution of a powder compact, and the amount of densification that has occurred all influence the homogeneity of the distribution of the liquid phase. In addition, the model predicts that, as shrinkage occurs or as the volume fraction of liquid phase increases, the pores will try to fill sequentially in order of increasing size. A consequence of this sequential filling of the pores is that the radius of curvature of the liquid meniscus, and hence the driving force for liquid‐phase sintering, changes systematically as shrinkage occurs. The modeling suggests that the driving force for sintering changes in a way that depends on the initial overall pore size distribution of the particle arrangement and the way the pore size distribution changes during sintering.
Phases in the System Ba2SiO4‐Ca2SiO4
Authors: MATKOVIĆ B. , POPOVIĆ S. , GRŽETA B. , HALLE R.
Published: March 2005

The system Ba2SiO4‐Ca2SiO4 was studied by heating mixtures of Ba2SiO4 and Ca2SiO4 at 1723 K. Six distinct phases resulted; they were examined by both X‐ray diffraction and differential thermal analysis. The phases β‐(Ba0.05Ca1.95)SiO4 and α‐(Ba0.15Ca1.85)SiO4 are isostructural with corresponding high‐temperature modifications of Ca2SiO4. The X phase (Ba0.48Ca1.52SiO4) is orthorhombic, is a pure phase rather than a solid solution, and is defined for the first time in the present work. The T phase (Ba1.31Ca0.69SiO4) is hexagonal and interpreted in terms of a unit cell with a doubled c parameter, in contrast with literature data.
Mechanical Properties of ZrC‐ZrB2 and ZrC‐TiB2 Directionally Solidified Eutectics
Authors: SORRELL CHARLES C. , STUBICAN VLADIMIR S. , BRADT RICHARD C.
Published: March 2005

Lamellar ZrC‐ZrB2 and Chinese‐script ZrC‐TiB2 eutectics were directionally solidified using the floating‐zone method of crystal growth. The Knoop microhardness, fracture toughness, and wear resistance were investigated as a function of the phase spacing. Nearly all of the direction ally solidified specimens exhibited superior mechanical properties when compared with the individual constituents. Notably high values of microhardness (24.02 GPa) and fracture toughness (5.44 MN/m3/4) were found for the ZrC‐ZrB2 eutectic.
Influence of Multiple Heterogeneities on Sintering Rates
Authors: Hsueh Chun‐Hway , Evans Anthony G. , Mcmeeking Robert M.
Published: March 2005

The sintering rate of a powder compact containing heterogeneities was calculated. The calculations reveal a strong retardation of sintering in the presence of nonsinterable agglomerates because of the development of a hydrostatic tensile stress. The variation in sintering rate with volume fraction is shown to be highly nonlinear, such that appreciable effects obtain even for 1% agglomerated powder. Specific results are calculated using constitutive laws pertinent to Al2O3.
Segregation of Mg to the (0001) Surface of Single‐Crystal Alumina: Quantification of AES Results
Authors: Baik Sunggi
Published: March 2005

The actual atomic concentration of Mg segregated to the basal plane of MgO‐doped single‐crystal alumina surfaces is calculated using an Auger electron spectroscopy quantification method which takes the backscattering factors and Auger electron escape depth into account. The results suggest that Mg segregates as effectively as Ca to AI2O3 interfaces. Plausible reasons why Mg has not been detected previously in the grain boundaries of MgO‐doped poly crystalline Al2O3, while Ca has always been found instead, are discussed.
Trivalent‐Cation‐Substituted Calcium Oxyhydroxyapatite
Authors: YAMASHITA KIMIHIRO , OWADA HITOSHI , NAKAGAWA HIROSHI , UMEGAKI TAKAO , KANAZAWA TAKAFUMI
Published: March 2005

Synthesis of stable oxy‐ and oxyhydroxyapatkes [(Ca,M)‐Ap] was attempted by substitution of Ca2+ with M3+ (M = Al, Y) assuming the composition Ca10‐xMx(PO4)6(OH)2‐xOx. Yttrium‐calcium oxyhydroxyapatite was successfully obtained. Its structure was analyzed and confirmed by X‐ray diffraction and infrared spectroscopy. Dielectric dispersion and absorption were not so distinct in (Ca,Y)‐Ap as in hydroxyapatite (Ca‐Ap). The ac electrical conductivity of (Ca10‐x,Yx)‐Ap was found to decrease with increasing x. These results are discussed in terms of a proposed charge transport mechanism.
Defect Clusters in Nonstoichiometric 3d Transition‐Metal Monoxides
Authors: GRIMES ROBIN W. , ANDERSON ALFRED B. , HEUER ARTHUR H.
Published: March 2005

The energies of defect clusters In Mn1–xO, Fe1–xO. Co1–xO, and Ni1–x,O have been calculated using molecular orbited theory. The results indicate that (i) relatively large extended defects of a zinc blende type coordination are stable in MnO and FeO, (ii) only small defects are stable in CoO, and (iii) no defect structures are stable in NiO.
Yttrium Segregation and YAG Precipitation at Surfaces of Yttrium‐ Doped α‐A12O3
Authors: McCune Robert C. , Donlon William T. , Ku Roland C.
Published: March 2005

Auger electron spectroscopy and low‐energy ion scattering were used to assess surface composition of yttrium‐doped polycrystalline and single‐crystal α‐aluminas which were heated under vacuum to temperatures above 1500°C. Extensive surface and intergranular precipitation of yttrium aluminum garnet was observed in a compact of nominal Y content of 210 wt ppm, while apparent Y segregation to surface cation sites predominated in a second compact with a Y content of 160 wt ppm. In the latter case, the segregation enthalpy of yttrium to the alumina surface in the temperature range 1700° to 1900°C was estimated to be of the order –44 kJ/mol with a maximum surface cation site occupancy of ∼13%.
Generation of Powder Compaction Response Diagrams
Authors: Matsumoto Roger L. K.
Published: March 2005

The effect of elastic compliances in the testing system is shown to have a considerable influence on the compaction diagram generated via an automatic procedure. Proper accounting of this effect allows rapid and accurate diagrams to be made.
On the Microstructures Resulting from the Diffusionless Cubic→Tetragonal Transformation in ZrO2‐Y2O3 Alloys
Authors: Lanteri V. , Chaim R. , Heuer A. H.
Published: March 2005

A diffusionless cubic (c)→metastable tetragonal (t′) phase transformation occurs in certain alloys in the ZrO2‐Y2O3 system on quenching from elevated temperatures. Microstructural features due to this phase transformation, principally anti‐phase domain boundaries (APB's) and mechanical accommodation twins, have been characterized using transmission electron microscopy. Certain differences between our interpretation and those of other workers are discussed.
Thermal Expansion of the Hexagonal (6H) Polytype of Silicon Carbide
Authors: LI Z. , BRADT R. C.
Published: March 2005

The thermal expansion of the hexagonal (6H) polytype of α‐SiC was measured from 20° to 1000°C by the X‐ray diffraction technique. The principal axial coefficients of thermal expansion were determined and can be expressed for that temperature range by second‐order polynomials: α11= 3.27 × 10–6+ 3.25 × 10–9T – 1.36 × 10–12T2 (1/°C), and ş33= 3.18 × 10–6+ 2.48 × 10–9T– 8.51 × 10–13T2 (1/°C). The σ11 is larger than α33 over the entire temperature range while the thermal expansion anisotropy, the δş value, increases continuously with increasing temperature from about 0.1 × 10–6/°C at room temperature to 0.4 × 10–6/°C at 1000°C. The thermal expansion and thermal expansion anisotropy are compared with previously published results for the (6H) polytype and are discussed relative to the structure.
Review and Chemical Thermodynamic Representation of 〈U1–zCezO2±x〉 and 〈U1–zLnzO2±x); Ln = Y, La; Nd, Gd
Authors: LINDEME TERRENCE B. , BRYNESTAD JORULF
Published: March 2005

The entire data base for the dependence of the nonstoichiometry, x, on temperature and chemical potential of oxygen (oxygen potential) in 〈U1–zCezO2+x〉 and 〈U1–zLnzO2+x〉 was retrieved from the literature and represented by a thermodynamic method. The method reproduces the behavior of the experimental data and also results in partial molal Gibbs free energy quantities that are useful for any thermodynamic calculation involving these nonstoichiometric phases. The behavior of these systems is also compared with that for 〈U1–zPuzO2±x〉.
Viscosity and Thermal Expansion of Mixed‐Alkali Borate Glasses
Authors: Kuppinger Christopher M. , Shelby James E.
Published: March 2005

Transformation‐range viscosity and thermal expansion measurements were made for five series (Li‐Na, Li‐K, Li‐Cs, Na‐Cs, and K‐Rb) of mixed‐alkali borate glasses containing 30 mol% total alkali oxide. In each case, negative deviations from additivity were observed in the isokom and glass transformation temperatures. Positive deviations from additivity were observed in the thermal expansion coefficients for the Li‐Na, Li‐K, and K‐Rb glasses, while the Li‐Cs and Na‐Cs glasses exhibited negative deviations. Maximization of the deviation from additivity in the viscosity and glass transformation temperatures occurred when the radius ratio of the two alkali ions was approximately 1.7 to 1.8. Combination of the results of this study with those of earlier studies indicates that the deviations from additivity observed for these properties are independent of the identity of the glass former.
Effect of Powder Purity and Second Phases on the Dielectric Properties of Lead Magnesium Niobate Ceramics
Authors: Chen Jie , Gorton Andrew , Chan Helen M. , Harmer Martin P.
Published: March 2005

The dielectric properties of lead magnesium niobate ceramics have been studied as a function of powder purity and microstructure. Starting powder purity was shown to have d pronounced effect on the resultant dielectric properties. Values of Kmax as high as 20 000 were obtained using starting powders of exceptionally high purity (99.999%), despite the formation of a pyrochlore phase. The pyrochlore phase formed as large isolated grains in the microstructure. It was found to be a cubic‐type pyrochlore with a composition of Pb2Nb1.75Mg0.25O6.62. Much lower dielectric constants were obtained with samples of lower reagent‐grade purity. This was partially explained by the presence of an intergranular second phase. Other factors such as lattice impurities and grain‐boundary chemistry were also argued to be important.
Effect of Nucleation on Transformation Toughening
Authors: LAMBROPOULOS J. C.
Published: March 2005

A simple model is presented to account for the effect of martensitic nucleation in ZrO2 particles on theoretical predictions of toughness enhancement during transformation toughening. The model allows for shear and volumetric strain contributions during nucleation, whereas only volumetric strain contributes to toughness enhancement. It is predicted that toughness enhancement results for both stationary and growing cracks. The predicted toughness enhancement exceeds the theoretical prediction for the case when only volumetric strain is allowed to operate. The important material property is identified to be the ratio of volumetric to shear strain during nucleation of the martensitic product in the transformation from tetragonal to monoclinic symmetry of the ZrO2 particles.
Crystallography of Stress‐Induced Martensitic Transformations in Partially Stabilized Zirconia
Authors: KELLY P. M. , BALL C. J.
Published: March 2005

The phenomenological theory of martensite crystallography was applied to the tetragonal‐monoclinic transformation in zirconia. Operation of variants of the lattice deformation can lead to a near‐twin orientation relation between different regions of a transformed particle, and if these regions are in the form of plates, as observed, they will fit together with very small contact stresses. Misfit stresses with the matrix are also minimized, and the overall misfit strain of a transformed particle is a very close approximation to a plane strain.
Preparation and Properties of Zirconia‐Toughened Mullite Ceramics
Authors: YUAN QI‐MING , TAN JIA‐QI , JIN ZHENG‐GUO
Published: March 2005

Compacts formed from high‐purity fused submicrometer mullite powders, both pure and with the additions of 5 to 25 vol% ZrO2 of particle size 1, 2, or 4 μm (average), were sintered in air at 1610°C for 6 h to form dense ceramic bodies. Mechanical properties (flexural strength, Kic, and Young's modulus) were measured both before and after thermal shock. The strength after thermal shock increased considerably in systems containing additions of 10 to 20 vol% ZrO2; Kic also increased, but not so markedly. The low fraction of tetragonal ZrO2 (0.1 to 0.2) in the as‐fired samples and the increase in Young's modulus after thermal shock for some strengthened samples supported the view that the interaction of residual internal stresses induced by quenching and the accompanying martensitic transformation of ZrO2 result in potential nucleation sites for microcracking. Thus, microcracking may be the predominant energy‐absorbing mechanism responsible for strengthening and toughening the quenched ceramic bodies.
Theoretical Estimates of Point Defect Energies in Cubic Zirconia
Authors: MACKRODT W. C. , WOODROW P. M.
Published: March 2005

Preliminary results of a theoretical study of lattice defects in cubic zirconia are presented.
Thermodynamics of Solid‐Solution Formation in NiO‐CuO
Authors: BULARZIK J. , DAVIES P.K. , NAVROTSKY A.
Published: March 2005

Samples in the (NixCu1‐x)O system, 0.5 ≤x≤ 1.0, have been examined using powder X‐ray diffraction and high‐temperature Solution calorimetry. According to the X‐ray characterization samples form a one‐phase rock salt solid solution up to x= 0.30, and crystallize with a tetragonal structure at x= 0.35. The enthalpies of mixing in the rock salt region of the system show large negative deviations from ideal mixing. The tetragonal compound does not show a large increase in enthalpic stability relative to the rock salt solid solutions. The variation of stability with composition is complex and suggests that substantial stabilization occurs at Ni‐rich compositions. The thermodynamic mixing properties have been interpreted in terms of cation order between the Ni and Cu ions. The degree of cation order appears to increase up to the composition x= 0.65 at which a compound with substantial cation order crystallizes with a tetragonally distorted structure. The calorimetric results correlate well with TEM observations of a complex microstrueture.
Dilatation of Porous Glass
Authors: SCHERER GEORGE W.
Published: March 2005

A porous body dilates when its surface energy changes, either by adsorption of a gas or by immersion in a liquid. A new equation is derived to describe the resultant strain and is shown to agree better with experiment than the equation proposed by Yates. The physical properties needed for the calculation include Young's modulus and surface area. Measurements are presented for a commercial porous glass that show that the modulus increases by a factor of ∼2, with negligible accompanying shrinkage, upon heating to 800°C. The increase is attributed to the presence of hydroxyls (nonbridging oxygens) in the solid phase that condense on heating. The surface area contains a large contribution from gel that precipitates in the pores during acid leaching. It is concluded that the gel is rigidly bound to the solid network, and therefore contributes to the dilation of the body Porous glasses show an anamolously large expansion when immersed in water, which is attributed to absorption of water into the solid phase. Diffusion of water into the solid phase is expected to be enhanced by the large concentration of nonbridging oxygens.
Tensile and Shear Properties of Laminated Ceramic Matrix Composites
Authors: SBAIZERO O. , EVANS A. G.
Published: March 2005

Symmetric (0°/90°) composite laminates consisting of SiC fibers in a lithifum aluminosilicate matrix have been tested intension and flexure. The various modes of damage, consisting of matrix cracks, delamination cracks, and fiber bundle failure, have been examined and related to features of the stress‐strain curves. The materials exhibit a relatively lower shear strength (20 MPa), measured in flexure, than tensile strength (200 MPa), because of the formation of matrix microcracks. The stress‐strain characteristics of the laminates are shown to be predictable, based on strength measurements obtained on the individual laminate layers, in conjunction with knowledge of the residual stresses.
Compensating Defects in Highly Donor‐Doped BaTiO3
Authors: CHAN HELEN M. , HARMER MARTIN R , SMYTH DONALD ML
Published: March 2005

Nb‐doped BaTiO3 has been prepared with various Ba/(Ti + Nb) ratios such that single‐phase products will be obtained if the charged donor center is assumed to be compensated in turn by Ba vacancies, Ti vacancies, equal concentrations of the two cation vacancies, oxygen interstitials, or electrons. For air‐Fired samples, examination by transmission electron microscopy showed that only the composition adjusted for compensation by titanium vacancies was single phase. The other compositions contained a Ti‐rich second phase in order to achieve a matrix with the appropriate concentration of titanium vacancies. When sintered in a reducing atmosphere, compensation was by electrons, and a Ba‐rich second phase was present hi the composition adjusted to give compensation by titanium vacancies. The results indicate that for donor concentrations greater than ∼0.5 mol% in BaTiO3, charge compensation is achieved by Ti vacancies under oxidizing conditions, and by electrons (as is well‐known) under reducing conditions.' The effect of compensating defects on grain growth is also discussed.
Coupled Grain Growth Effects in Al2O3/10 vol% ZrO2
Authors: Pugar Eloise A. , Morgan Peter E. D.
Published: March 2005

Coupled crystallization has been observed in the Al3O3/10%‐ZrO2 system by heating an amorphous precursor Al /Zr copolymerized alkoxide network structure. A finely divided two‐phase material results which stabilizes tetragonal ZrO2 to 1700°C and exhibits an unprecedented microstructure. During crystallization, the grain growth of ZrO2 is coupled to the γ→α phase transformation of Al2O3.
Change in Chemical Composition of Mullite Formed from 2SiO2°3Al2O3 Xerogel During the Formation Process
Authors: Okada Kiyoshi , ŌTslka Nozomu
Published: March 2005

The chemical composition of mullite which was termed from 2SiO23Al2O3 xerogel by firing was examined by analytical TEM. Mullite formed at 950°C firing showed around 66 mol% Al2O3, which was fairly Al2O3 rich compared with the bulk composition. The chemical composition of mullite gradually approached the bulk composition as the firing temperature increased to 1400°C and slightly departed again above that firing temperature.
Dielectric Measurements of Package Materials in an Inhomogeneously Filled Rectangular Waveguide
Authors: Dube D.C. , Lanagan Michael T. , Jang Ski‐Joo
Published: March 2005

A transmission technique for dielectric measurements in the microwave region is presented. Thin specimens are longitudinally positioned at the center of a rectangular waveguide. Expressions for the real and imaginary parts of the permittivity are considered with different approximations. The suitability of the technique is evaluated for dielectric measurements of packaging materials. Experimental results are presented for Teflon, porous Vycor, and alumina in the X‐band frequency range.
Photosensitive Characteristics of Dopant‐Free, Ultraviolet‐Sensitive Calcium Aluminate Glasses
Authors: HOSONO HIDEO , YAMAZAKI KOJI , ABE YOSHIHIRO
Published: March 2005

Calcium aluminate glasses show high sensitivity to ultraviolet radiation without the doping of optically active components. In this paper, photosensitive characteristics and the cause of UV‐induced coloring were investigated for these glasses. Ultraviolet rays below 270 nm were effective for inducing the coloring. The most effective wavelength agreed with that of the apparent absorption edge. In the ternary system with SiO2 or GeO2, the sensitivity was monotonically reduced with the amount of the third component and almost vanished for the compositions containing 40 mol%. On the basis of the establishment of a close correlation between two optical absorption bands and two electron spin resonance signals induced by UV illumination, the UV‐induced coloring was concluded to be due to the emergence of an aluminum‐oxygen hole center (Al‐OHC) and an ozonide (O3‐).
Synthesis and Thermal Stability of Aluminum Titanate Solid Solutions
Authors: ISHITSUKA MASAYUKI , SATO TSUGIO , ENDO TADASHI , SHIMADA MASAHIKO
Published: March 2005

Aluminum titanate solid solutions with empirical formulas of Al2Ti1‐xZrxO5, Al6(2‐x)(6+x)Si6x/(6+x)□6x/(6+x)TiO5, and Al2(1‐x)MgxTi1+xO5 were synthesized by reaction sintering and annealed at 900° to 1300°C in air to evaluate the thermal stability. Substitution of Al in Al2TiO5 by Si and 2Al by Mg and Ti ions to form solid solutions such as AI6(2‐x)/(6+x)l‐Si6x/(6+x)□6x/(6+x)TiO5, and Al2(1‐x)MgxTi1+xO5 was effective in controlling the thermal decomposition, but substitution of Ti by Zr had little effect.
Spectroscopic Analysis of the Structure of Silicate Glasses along the Joint xMAlO2‐(1–x)SiO2(M = Li, Na, K, Rb, Cs)
Authors: ROY BIMALENDU NARAYAN
Published: March 2005

Infrared spectroscopic studies of charge‐coupled substitution in silicate glasses and crystals along the joints xMAlO2(1 –x)SiO2 (M = Li, Na, K, Rb, and Cs; 0.10 ≤x≤ 0.60) were carried out in the range 2000 to 200 cm−1 Three major absorption bands appeared in the 1100‐, 800‐, and 500‐cm−1 regions. For a specific value of x, the observed changes in frequency, intensity, and bandwidth decreased in the order Li > Na > K > Rb > Cs and the apparent disorder in the glass structure caused by the substituted aluminum increased in the direction K < Na < Li. The 800‐cm−1 band splits at SiO2≃ 0.75 mol, which has been interpreted in terms of the number of AlO4 tetrahedra in the structure. Most of the substituted aluminum in the glasses and the crystals was found to be in the fourfold coordination.
Crack Deflection as a Toughening Mechanism in SiC‐Whisker‐Reinforced MoSi2
Authors: Carter David H. , Hurley George F.
Published: March 2005

Crack propagation in SiC‐whisker‐reinforced MoSi2 was studied. In particular, the deflection angles of the cracks were examined to determine the degree to which they are affected by the whisker reinforcement. The composite studied was hot‐pressed MoSi2 with 20 vol% vapor‐liquid‐solid β‐SiC whiskers. A substantial difference was found between the deflection angles of cracks formed in the reinforced MoSi2 and those in a control sample with no whiskers, showing the process of crack deflection as an important, but not the only, toughening mechanism.
On the Polymorphism of Enstatite
Authors: LEE W. E. , HEUER A. H.
Published: March 2005

The polymorphism of enstatite (MgSiO3) is reviewed. Three stable phases occur—clinoenstatite, orthoenstatite, and protoenstatite, being stable at low, intermediate, and elevated temperatures, respectively — and new data concerning their crystallization from synthetic glasses are summarized. The phase transformations between these polymorphs are discussed, particularly their sensitivity to shear stresses. Finally, the possibility of using one or more of these transformations for toughening silicates is considered.
Frictional Properties of Sintered TiN‐TiB2 and Ti(CN)‐TiB2 Ceramics at High Temperature
Authors: Shobu Kazuhisa , Watanabe Tadahiko , Enomoto Yuji , Umeda Kazunori , Tsuya Yuko
Published: March 2005

The frictional properties of sintered TiN‐TiB2 and Ti(CN)‐TiB2 ceramics were investigated in air at temperatures up to 1073 K. Friction coefficients as low as 0.1 to 0.2 can be obtained at 973 to 1073 K because oxidation of TiB2 produces a lubricating, glassy phase of boron oxide on the sliding surfaces.
Eutectoid Decomposition of MgO‐Partially‐Stabilized ZrO2
Authors: FARMER SERENE C. , HEUER ARTHUR H. , HANNINK R. H. J.
Published: March 2005

Euctectoid decomposition of cubic (c) ZrO2 in MgO‐partially‐stabilized ZrO2 (Mg‐PSZ) has been studied using optical, scanning electron, and transmission electron microscopy. Alloys containing from 8.1 to 18.6 mol% MgO were decomposed by annealing between 1100° and 1300°C for times up to 16 h. The eutectoid products nucleated heterogeneously at the grain boundaries and advanced into the adjoining two‐phase grains. Decomposition proceeded as a “cellular” reaction involving the cooperative growth of MgO and a low‐solute ZrO2 phase with either monoclinic (m) or tetragonal (t) symmetry. The MgO morphology is rodlike and exhibits a well‐defined orientation relationship to m‐ZrO2. The rate of eutectoid decomposition was a maximum at 1200°C and was greater in the solute‐rich materials at all temperatures. At 1100°C, SrO doping decreased the nucleation rate of the eutectoid product in a 9.7 mol% alloy, thus strongly suppressing the decomposition rates; at the higher decomposition temperatures, the SrO was less effective.
Crystallization Kinetics of a Complex Lithium Silicate Glass‐Ceramic
Authors: HAMMETTER WILLIAM F. , LOEHMAN RONALD E.
Published: March 2005

Volume crystallization of this glass is nucleated by Li3PO4. On heating from room temperature, Li2SiO3 appears around 650°C and then converts to Li2Si2O5 around 850°C by reaction with SiO2 from the melt. Preheating the glass at 1000°C forms larger Li3PO4 nuclei that promote additional crystallization of cristobalite in the 650° to 850°C range. Crystallization activation energies calculated from scan‐rate dependence of DTA peaks are 270 kJ/mol for Li2SiO3 and 360 to 570 kJ/mol for Li2Si2O5.
Retention of Cobalt, Cesium, and Strontium in the Hydrates of C3S, C3A, and Gypsum
Authors: LAMEILLE J.M. , GOUTIERE G. , PETIT JEAN‐CLAUDE , REGOURD MICHELINE
Published: March 2005

The retention of cobalt, cesium, and strontium as trace elements in the hydrates of simple ordinary portland cement components has been investigated. The combined characterization of the solid by SEM, electron microprobe, XRD, and SIMS, as well as the chemical analysis of the solutions, allowed us to identify the likely localization of these trace elements in the solid. In particular, cobalt is dramatically incorporated into the solid during the hydration of C3S; we show that this is due to the formation of a cobalt oxychloride, a compound which is unstable at temperatures ≥60°C. Cesium is retained in small amounts in the C‐S‐H and CH mixture. The formation of hydrated aluminates notably increases its retention. Finally, small quantities of strontium are also retained in silicates and, in the presence of gypsum, its retention is markedly higher. This is likely due to the formation of sulfoaluminates.
Oxidation Kinetics of Polycrystalline LaCrO3
Authors: Yu Chikung J. , Sparlin Don M. , Anderson Harlan U.
Published: March 2005

The oxidation kinetics of polycrystalline LaCrO3 were determined by measuring the time and temperature dependence of the weight and conductivity change of reduced samples. A region of fast diffusion followed by a smaller, slower diffusion “tail” was observed in the thermogravimetric measurements. This observation can be interpreted as the rapid diffusion along the grain boundaries and subsequent diffusion into the body of the grain. The absence of the “tail” in the conductivity measurements is due to the high hole mobility along the boundaries.
Optical, Structural, and Chemical Characteristics of Lead‐Indium Phosphate and Lead‐Scandium Phosphate Glasses
Authors: SALES BRIAN C. , BOATNER LYNN A.
Published: March 2005

Two new glass systems based on a range of lead‐indium phosphate and lead‐scandium phosphate compositions have been developed and characterized. These glasses have a relatively high index of refraction (n= 1.75 to 1.83) in the visible region and exhibit moderate dispersion (Abbe number ∼30). The ultraviolet absorption edge occurs near 300 nm and the glasses strongly absorb in the infrared at wavelengths greater than 2800 nm. Both glass types can be prepared at relatively low temperatures (900° to 1000°C) and are easily poured down to ∼800°C because of their low melt viscosities. The glasses exhibit good chemical durability and resistance to both weathering and intense γ‐radiation. These materials have a glass transition temperature of about 430°C, a softening point of about 460°C, and thermal expansion coefficients in the range of 10.8 × 10−6 to 12.0 × 10−6/°C. The structure of these phosphate glasses is shown to consist of a distribution of chains of PO4 tetrahedra held together by bonding between the non‐bridging oxygens of the tetrahedra and the metal cations. The polyphosphate chain length distribution was determined by a liquid chromatographic technique. Potential aqueous corrosion mechanisms are discussed and some general guidelines for forming a chemically durable phosphate glass are given.
Electrical Conductivity and Defect Models of MgO‐Doped Cr2O3
Authors: PARK JIN SEONG , KIM HO GI
Published: March 2005

The dc electrical conductivity of MgO‐doped Cr2O3 and the defect models with the defect structure of a sesquioxide were investigated as a function of oxygen partial pressure, temperature, and dopant content. The electrical conductivity of MgO‐doped Cr2O3 is increased with oxygen partial pressure and temperature. The electrical conductivity of MgO‐doped Cr2O3 within the solubility limit is increased with MgO content because of the creation of holes and the annihilation of chromium vacancies. Above the solubility limit, however, it is decreased with increasing MgO content owing to the formation of the spinel phase (MgCr2O4).