bluuebunny/crossref_metadata_2025 huggingface dataset:
Health Plan Switching and Attrition Bias in the RAND Health Insurance Experiment
Authors: Nyman John A.
Published: March 2008

One of the most influential “lessons” of the RAND Health Insurance Experiment (HIE) is that cost sharing can reduce hospitalizations by about a quarter, with no effect on health for the average adult. In an earlier paper in this journal, I suggested that a portion of this reduction is due to participants becoming ill and dropping out of the experiment in order to switch to their preexperiment insurance coverage and thus avoid paying the cost-sharing amount. The sixteenfold higher voluntary attrition rate in the cost-sharing arms provides compelling evidence in support of this alternative explanation. Evidence is also provided by the finding in Manning, Duan, Keeler (1993) that the predicted number of hospitalizations among those who dropped out of the coinsurance arms was significantly greater by 34.5 percent than the actual number of hospitalizations, suggesting that participants anticipate hospitalizations and leave the experiment before incurring the cost-sharing payment. Still more evidence is provided by the finding that those (cost-sharing) participants with greater incomes, instead of being more likely to be hospitalized, as greater income usually implies, were less likely to be hospitalized than poor participants. This finding is consistent with their having better preexperiment insurance coverage than poor participants and therefore being more likely to have an incentive to drop out. This inpatient attrition bias makes it dangerous to rely on this lesson of the HIE, because it is not clear that hospitalizations were actually reduced by one-quarter, much less that if such a reduction actually had occurred, there would be no health consequences.
APC/CFzr/Cdh1 promotes cell cycle progression during theDrosophilaendocycle
Authors: Narbonne-Reveau Karine , Senger Stefania , Pal Margit , Herr Anabel , Richardson Helena E. , Asano Maki , Deak Peter , Lilly Mary A.
Published: March 2008

The endocycle is a commonly observed variant cell cycle in which cells undergo repeated rounds of DNA replication with no intervening mitosis. How the cell cycle machinery is modified to transform a mitotic cycle into endocycle has long been a matter of interest. In both plants and animals, the transition from the mitotic cycle to the endocycle requires Fzr/Cdh1, a positive regulator of the Anaphase-Promoting Complex/Cyclosome (APC/C). However, because many of its targets are transcriptionally downregulated upon entry into the endocycle, it remains unclear whether the APC/C functions beyond the mitotic/endocycle boundary. Here, we report that APC/CFzr/Cdh1 activity is required to promote the G/S oscillation of the Drosophila endocycle. We demonstrate that compromising APC/C activity, after cells have entered the endocycle, inhibits DNA replication and results in the accumulation of multiple APC/C targets, including the mitotic cyclins and Geminin. Notably, our data suggest that the activity of APC/CFzr/Cdh1 during the endocycle is not continuous but is cyclic,as demonstrated by the APC/C-dependent oscillation of the pre-replication complex component Orc1. Taken together, our data suggest a model in which the cyclic activity of APC/CFzr/Cdh1 during the Drosophilaendocycle is driven by the periodic inhibition of Fzr/Cdh1 by Cyclin E/Cdk2. We propose that, as is observed in mitotic cycles, during endocycles,APC/CFzr/Cdh1 functions to reduce the levels of the mitotic cyclins and Geminin in order to facilitate the relicensing of DNA replication origins and cell cycle progression.
Six2 functions redundantly immediately downstream of Hoxa2
Authors: Kutejova Eva , Engist Bettina , Self Michelle , Oliver Guillermo , Kirilenko Pavel , Bobola Nicoletta
Published: March 2008

Hox transcription factors control morphogenesis along the head-tail axis of bilaterians. Because their direct functional targets are still poorly understood in vertebrates, it remains unclear how the positional information encoded by Hox genes is translated into morphogenetic changes. Here, we conclusively demonstrate that Six2 is a direct downstream target of Hoxa2 in vivo and show that the ectopic expression of Six2, observed in the absence of Hoxa2, contributes to the Hoxa2 mouse mutant phenotype. We propose that Six2 acts to mediate Hoxa2 control over the insulin-like growth factor pathway during branchial arch development.
Smectite-illite-muscovite transformations, quartz dissolution, and Silica release in shales
Authors: van de Kamp Peter C.
Published: March 2008

Quantitative analysis of the smectite-to-illite and illite-to-muscovite transformations indicates that 17–28 wt.% SiO2 and 17–23 wt.% SiO2, respectively, are liberated during these reactions, assuming that Al is conserved. Dissolution of quartz silt in shales yields up to 6–9% SiO2 in the range up to 200°C and a further 10–15% SiO2 in the 200–500°C range. For muds altered to shales at 200°C, 14–20 wt.% silica is evolved. From 200 to 500°C, a further 18–28 wt.% silica is evolved. Additional small amounts of silica may be released in the alteration of feldspar to clay and by stylolitization of quartz silt. Thus, in the burial and temperature range of diagenesis into the epizone, major quantities of silica are released from clays and by quartz dissolution in shales. Within this range of alteration, concomitant decline of whole-rock Si/Al (SiO2/Al2O3) in the transformation of smectite to illite to muscovite suggests the liberated silica migrates from the source shale. As a result, the metamorphosed shales are more micaceous and less quartzose than their progenitor muds. In the diagenetic zone and anchizone, the evolved silica is probably a major source of quartz cement in sandstones. In the epizone, evolved silica is commonly present in quartz veins in the parent rocks. Fluid-inclusion temperatures in quartz overgrowths and fracture fillings in some sandstones suggest that some cements may have been derived from downdip basinal shales and pressure solution in sandstones.
Pyroxene weathering to smectite: Conventional and cryo-field emission scanning electron microscopy, Koua Bocca ultramafic complex, Ivory Coast
Authors: Velbel Michael A. , Barker William W.
Published: March 2008

Air-dried and high-pressure frozen/freeze-etched samples of clinopyroxene and smectite in a saprolitized clinopyroxenite from Koua Bocca, Ivory Coast, West Africa, were compared to characterize textures developed during natural weathering of chain silicates. Comparison with air-dried material allowed evaluation of high-pressure cryofixation as a technique for preserving textures of hydrated clay minerals. Air-dried pyroxene surfaces appear very smooth. Small, flat lamellae, oriented parallel to the c axis, lend a distinct splintery appearance to pyroxene surfaces in fully hydrated samples. These lamellae often display a combination of straight (110) pyroxene edges and a crinkled border, suggestive of smectite. Narrow lenticular (110) open cleavages occur in both preparations and are not a pressurization artifact. Most often these openings contain no secondary minerals. Spaces between pyroxene denticles, lined with collapsed smectite in air-dried samples, are filled with thin packets of anhedral smectite crystallites oriented face to face when hydrated. Smectite microboxwork preserves original topotactic textures developed during isovolumetric pyroxene transformation, and smaller nanoporosity appears in hydrated cryofixed examples. Occasional regions of edge-to-face ‘house of cards’ texture also occur. Elimination of sample preparation artifacts induced by surface tension during air drying demonstrates that pores actually present during a hydration reaction-driven weathering episode are smaller and more numerous than would be inferred from examining air-dried materials.
Adjuvant activity of type I interferons
Authors: Tovey Michael G. , Lallemand Christophe , Thyphronitis George
Published: March 2008

Type I interferons (IFNs) produced primarily by plasmacytoid dendritic cells (pDCs) as part of the innate immune response to infectious agents induce the maturation of myeloid DCs and enhance antigen presentation. Type I IFNs also enhance apoptosis of virus-infected cells, stimulate cross priming and enhanced presentation of viral peptides. Type I IFNs are powerful polyclonal B-cell activators that induce a strong primary humoral immune response characterized by isotype switching and protection against virus challenge. Type I IFNs stimulate an IgG2a antibody response characteristic of Th1 immunity when ad-mixed with influenza virus vaccine and injected intramuscurarly (i.m.) or administered intranasally. The adjuvant activity of type I IFNs has been shown to involve direct effects of IFN on B-cells, effects on T-cells, as well as effects on antigen presentation. Oromucosal administration of type I IFNs concomitantly with i.m. injection of vaccine alone can also enhance the antibody response to influenza vaccination by enhancing trafficking of antigen-presenting cells towards the site of vaccination. Recombinant IFNs are potent adjuvants that may find application in both parenterally and mucosally administered vaccines.
Non-regulatory CD8+CD45RO+CD25+ T-lymphocytes may compensate for the loss of antigen-inexperienced CD8+CD45RA+ T-cells in old age
Authors: Herndler-Brandstetter Dietmar , Veel Ellen , Laschober Gerhard T. , Pfister Gerald , Brunner Stefan , Walcher Susanne , Parson Walther , Lepperdinger Günter , Grubeck-Loebenstein Beatrix
Published: March 2008

The age-related decline in immune system functions is responsible for the increased prevalence of infectious diseases and the low efficacy of vaccination in elderly individuals. In particular, the number of peripheral naive T-cells declines throughout life and they exhibit severe functional defects at advanced age. However, we have recently identified a non-regulatory CD8+CD45RO+CD25+ T-cell subset that occurs in a subgroup of healthy elderly individuals, who still exhibit an intact humoral immune response following influenza vaccination. Here, we demonstrate that CD8+CD45RO+CD25+ T-cells share phenotypic and functional characteristics with naive CD8+CD45RA+CD28+ T-cells from young individuals, despite their expression of CD45RO. CD8+CD45RO+CD25+ T-cells also have long telomeres and upon antigenic challenge, they efficiently expand in vitro and differentiate into functional effector cells. The expanded population also maintains a diverse T-cell receptor repertoire. In conclusion, CD8+CD45RO+CD25+ T-cells from elderly individuals compensate for the loss of functional naive T-cells and may therefore be used as a marker of immunological competence in old age.
Novel strategies to identify biomarkers in tuberculosis
Authors: Jacobsen Marc , Mattow Jens , Repsilber Dirk , Kaufmann Stefan H.E.
Published: March 2008

The more we learn about the immune response against tuberculosis (TB) and particularly about the features which distinguish protective immunity, disease susceptibility and pathology, the better we can define biomarkers which correlate with these different stages of infection. The most widely used biomarker in TB, which without a doubt is an important component of protective immunity, is IFNγ secreted by antigen-specific CD4 T-cells. However, the complexity of the immune response against TB makes it more than likely that additional biomarkers are required for a reliable correlate of protection. As a corollary, we assume that a set of biomarkers will be required, termed a biosignature.
Inhibition of bacterial oxidases by formamide and analogs
Authors: Gupta Sayan , Mazumdar Shyamalava
Published: March 2008

The enzymatic activity of Paracoccus denitrificans cytochrome c oxidase (COX) and Escherichia coli cytochrome b
o ubiquinol oxidase (QOX) was determined in the presence of formamide, N,N-dimethyl formamide and N,N-dimethyl acetamide. Formamide was found to inhibit the enzyme activity of the oxidases most significantly, whereas the other two compounds inhibited the activity to a lesser extent. The effects of formamide and analogs on enzyme activity were very similar for COX and QOX, indicating that the mechanism of inhibition might be the same for both of these oxidases. The inhibition kinetics followed a non-competitive mechanism. Studies using proteoliposomes of COX and QOX containing the electron entry site of the enzyme directed towards the outside of the vesicles showed that the effect of inhibition by formamide was higher when the inhibitor was present on the outside of the proteoliposome compared to when it was present only in the aqueous core. This indicates that inhibition of enzyme activity by formamide possibly predominantly involves blocking of the water exit pathway in the oxidases.
Adaptive immune responses to hepatitis C virus: from viral immunobiology to a vaccine
Authors: Thimme Robert , Neumann-Haefelin Christoph , Boettler Tobias , Blum Hubert E.
Published: March 2008

Hepatitis C virus (HCV) causes chronic infection in approximately two-thirds of cases, leading to chronic hepatitis, liver cirrhosis, liver disease, liver failure, and hepatocellular carcinoma in a substantial proportion of the 170 million HCV-infected individuals worldwide. It is generally accepted that the cellular immune response plays the most important role in determining the outcome of HCV infection. First, vigorous, multispecific and sustained CD4+and CD8+T-cell responses are associated with viral clearance. Second, depletion studies in chimpanzees, the only other host of HCV besides humans, have shown that both CD4+and CD8+T-cells are required for virus elimination. Third, the host's human leukocyte antigen alleles, which restrict the repertoire of CD4+and CD8+T-cell responses, influence the outcome of infection. Of note, protective immunity has been demonstrated in population-based studies, as well as in experimentally infected chimpanzees. Thus, a detailed understanding of the mechanisms contributing to the failure of the antiviral immune response should allow successful development of prophylactic and therapeutic vaccination strategies.
Japanese encephalitis vaccines – needs, flaws and achievements
Authors: Tauber Erich , Dewasthaly Shailesh
Published: March 2008

Japanese encephalitis causes serious health problems in countries in Southeast Asia, where the causative virus is endemic. Whereas most adults living in this region have acquired immunity, children are at high risk of infection. Childhood mass immunization programs with first-generation mouse brain-derived vaccines efficiently reduced Japanese encephalitis incidence in affected countries, but immunization recommendations have mostly been abolished in Japan owing to the occurrence of severe side effects. Thus, there is a pressing need for safer vaccines to keep the disease under control. The safety profile of the current vaccines, together with the relatively low incidence, makes the risk/benefit ratio unfavorable for immunization of travelers to Southeast Asia, despite the high mortality once the clinical disease has developed. As Asian countries become increasingly popular travel destinations, the availability of well-tolerated vaccines would likely shift the ratio towards immunization. Currently, there is one second-generation inactivated cell-culture-grown vaccine in late-stage clinical development that is approaching licensing in developed countries.
Construction of an encapsulated ESAT-6-based anti-TB DNA vaccine and evaluation of its immunogenic properties
Authors: Nosareva Olesya , Nesterov Andrey , Boldyrev Alexander , Smirnova Olga , Tumanov Yurii , Kouzmitcheva Galina , Tatkov Sergey
Published: March 2008

Experimental preparations based on a DNA vaccine encoding the ESAT-6 antigen of Mycobacterium tuberculosis have been obtained (KpONE6) and studied for immunogenic effects in the murine model. The core of the preparation contains DNA of the recombinant plasmid pONE6 encapsulated within a spermidine-polyglucin conjugate, thereby protecting the DNA vaccine from degradation. KpONE6 induces a proliferative T-cell immune response in mice upon intramuscular immunization.
The coming of age of virus-like particle vaccines
Authors: Jennings Gary T. , Bachmann Martin F.
Published: March 2008

Virus-like particles are supra-molecular assemblages, usually icosahedral or rod-like structures. They incorporate key immunologic features of viruses which include repetitive surfaces, particulate structures and induction of innate immunity through activation of pathogen-associated molecular-pattern recognition receptors. They carry no replicative genetic information and can be produced recombinantly in large scale. Virus-like particles thus represent a safe and effective vaccine platform for inducing potent B- and T-cell responses. In addition to being effective vaccines against the corresponding virus from which they are derived, virus-like particles can also be used to present foreign epitopes to the immune system. This can be achieved by genetic fusion or chemical conjugation. This technological innovation has greatly broadened the scope of their use, from immunizing against microbial pathogens to immunotherapy for chronic diseases. Towards this end, virus-like particles have been used to induce autoantibodies to disease-associated self-molecules involved in chronic diseases, such as hypertension and Alzheimer's disease. The recognition of the potent immunogenicity and commercial potential for virus-like particles has greatly accelerated research and development activities. During the last decade, two prophylactic virus-like particle vaccines have been registered for human use, while another 12 vaccines entered clinical development.
Synchrotron x-ray study of interstitial oxygen ordering in the superconducting phase of La2CuO4+δ
Authors: Xiong X. , Zhu Q. , Li Z. G. , Moss S. C. , Feng H. H. , Hor P. H. , Cox D.E. , Bhavaraju S. , Jacobson A. J.
Published: March 2008

A synchrotron x-ray powder-diffraction study has been carried out on two samples with well-defined excess oxygen concentrations, δ = 0.045 and 0.055. Evidence for one-dimensional interstitial oxygen ordering along the c -axis was observed from the appearance of a pair of superlattice satellite peaks at (0, 1,2 ± Δ) in both samples. In La2CuO4.045, a ∼5% oxygen-poor Bmab phase coexists with a stage-6 phase and with a small amount of the high-temperature-tetragonal (HTT) phase below the phase separation temperature (∼280 K). La2CuO4.055 shows a single stage-5 phase below 170 K, but with two unindexed peaks between (0, 1, 2 ± 0.2) satellites which may well result from a further domain modulation. The critical temperature Tc is increased by 1.5 K by reducing the stage number from 6 to 5.
Al2O3 additions for isothermal melt processing of Bi2Sr2CaCu2Oy
Authors: Holesinger T.G.
Published: March 2008

It is shown that additions of Al2O3 (1.0 wt. %) can significantly aid in the isothermal melt processing of Bi2Sr2CaCu2Oy (Bi-2212). Al2O3 additions provide a means for grain refinement of phases present in the partial melt. By limiting grain growth in the partial melt, solidification to form Bi-2212 proceeds more efficiently, resulting in fewer secondary phases and improved transport properties. Aluminum does not substitute into the superconducting phase to any appreciable extent and is present in fully processed material as small, secondary grains of approximate composition Sr2−xCaxAlOy or Bi2Sr4−xCaxAl3Oy · Al2O3 additions were applied to the isothermal melt processing of Bi-2212 thick films and current leads.
Low-energy electron beam induced regrowth of isolated amorphous zones in Si and Ge
Authors: Jenčič I. , Robertson I. M.
Published: March 2008

Spatially isolated amorphous regions in Si and Ge have been regrown at room temperature by using an electron beam with an energy less than that required to cause displacement damage in crystalline material. The rate at which the zones regrow is a function of the energy of the electron beam. As the electron energy is increased from 25 keV (lowest energy employed), the regrowth rate decreases and reaches a minimum below the threshold displacement voltage. With further increases in the electron energy, the rate again increases. It is suggested that at the lower electron energies this room temperature regrowth process is stimulated by electronic excitation rather than by displacive-type processes.
On the substrate temperature dependence of the properties of In0.52Al0.48As/InP structures grown by molecular beam epitaxy
Authors: Yoon S.F. , Miao Y. B. , Radhakrishnan K. , Swaminathan S.
Published: March 2008

Growth of In0.52Al0.48As epilayers on InP(100) substrates by molecular beam epitaxy at a wide range of substrate temperatures (470–550 °C) is carried out. Low temperature photoluminescence (PL) and double-axis x-ray diffraction (XRD) measurements showed a strong dependence of the PL and XRD linewidths and lattice mismatch on the substrate temperature. Minimum PL and XRD linewidths and lattice mismatch were found to occur at substrate temperatures of between ≈500 and 520 °C under the beam fluxes used in this study. The XRD intensity ratios (Iepi/Isub) were generally higher within the same substrate temperature range at which the lattice mismatch was the lowest. XRD rocking curves of samples grown at low temperatures showed the main epilayer peak to be composed of smaller discrete peaks, suggesting the presence of regions with different lattice constants in the material. PL spectra taken at increasing temperatures showed the quenching of the main emission peak followed by the evolution of a distinct lower energy peak which is possibly associated with deep lying centers.
Solidification of Al–Cu–Fe alloys forming icosahedral phase
Authors: Grushko B. , Wittenberg R. , Holland-Moritz D.
Published: March 2008

The solidification of a series of Al–Cu–Fe alloys containing an icosahedral phase has been studied by scanning electron microscopy, energy-dispersive x-ray spectroscopy, powder x-ray diffraction, and differential thermal analysis. The constitution and morphology of alloys solidified at different rates are presented. The overall compositional range of the icosahedral phase was determined in as-cast, slowly solidified alloys and those annealed at 800 and 600 °C. The solidification of this phase follows closely the Al3Fe–AlCu compositional direction. The first icosahedral phase solidified close to Al65.5Cu21.5Fe13; its compositional region at 800 °C lies between about Al64.5Cu23Fe12.5 and Al62Cu26.5Fe11.5, while at 600 °C it lies between Al62Cu26.5Fe11.5 and Al60.5Cu29.5Fe10. The formation of the icosahedral and related structures observed in Al–Cu–Fe alloys is discussed.
Effects of hydrogen on the microstructure and microchemistry of Ti3Al – Nb intermetallics at high temperatures and high pressures
Authors: Xiao H. Z. , Robertson I. M. , Birnbaum H. K.
Published: March 2008

The microstructural and microchemical changes produced in a Ti–25Al–10Nb–3V–1Mo alloy (at. %) by charging at high temperatures in high pressures of hydrogen gas have been studied using transmission electron microscopy (TEM) and x-ray methods. Hydrides incorporating all of the substitutional solutes that formed during charging have a face-centered cubic (fcc) structure and exhibit either a plate or fine-grained morphology. With increasing hydrogen content, the size of the hydrides decreases and their microchemistry changes as they approach the stable binary hydride, TiH2. Rejection of substitutional solute elements from the hydride produces changes in the microchemistry, and consequently in the crystal structure, of the surrounding matrix. In alloys containing 50 at. % H, this solute redistribution results in the formation of an orthohombic substitutional solid solution phase containing increased levels of Nb. The driving force of this redistribution of solutes is the reduction in the chemical potential of the system as the amount of the most stable hydride, TiH2, forms. The hydrides reverted to a solid solution on annealing in vacuum at 1073 K, and the original microchemistry of the alloy was restored. Reversion from the hydride structure to the original α2 ordered DO19 structure proceeds via a disordered HCP phase.
Electronic bonding characteristics of hydrogen in bcc iron: Part I. Interstitials
Authors: Itsumi Yoshio , Ellis D. E.
Published: March 2008

Electronic structure calculations were carried out for bcc iron (Fe) clusters with or without hydrogen (H), and also involving a vacancy, using the self-consistent Discrete Variational method (DV-Xα) within the local density functional formalism. Bonding characteristics investigated show the following: (i) Interstitial H notably decreases interatomic Fe–Fe bond strengths, but acts over a small distance (within 0.3 nm). (ii) In the perfect Fe lattice field, interstitial H feels a repulsive force at any site. As a result of lattice relaxation, volume expansion may be expected. (iii) H in combination with a vacancy prefers a position shifted from the octahedral site toward the vacancy. This is fairly consistent with an experimental result.
Electronic bonding characteristics of hydrogen in bcc iron: Part II. Grain boundaries
Authors: Itsumi Yoshio , Ellis D.E.
Published: March 2008

Electronic structure calculations were carried out for bcc iron grain boundaries (GB) with or without hydrogen, using the self-consistent Discrete Variational embedded cluster method within the first-principles local density formalism. Bonding characteristics were mainly investigated. Simple rigid body translations perpendicular to the GB plane were used for estimation of relaxed GB geometry. Analysis of bond order summation over the GB shows considerable volume expansion normal to the GB plane of a dense 23(111) twist/tilt GB and some compression for the rather open 23(110) twist configuration. These results are discussed in the context of atomistic simulations which suggest that higher energy GB's generally have larger volume expansion normal to the GB plane. H in a 23(111) GB reduces Fe-Fe bonding strength by —3% within a 0.25 nm spherical volume around the H site, associated with reduction of the 4s and 4p occupancy of the nearest neighbor Fe. Since these orbitals contribute mainly to metallic bonding, the action of H atoms as an embrittlement inducer can be understood.
A new design of tungsten carbide tools with diamond coatings
Authors: Weihnacht Volker , Fan W.D. , Jagannadham K. , Narayan J. , Liu C-T.
Published: March 2008

We have designed tungsten carbide tools with a new binder, which makes them suitable for advanced diamond tool coatings. The new tool substrates, made of tungsten carbide and nickel aluminide as binder phase, are produced by sintering and hot isostatic pressing, and also by combustion synthesis. The high temperature strength of nickel aluminide is key to superior tool performance at elevated temperatures. More importantly, nickel aluminides reduce the formation of graphite and promote diamond growth during chemical vapor deposition. Diamond films are deposited on the new tool substrates to investigate the nucleation density, adhesion, and wear resistance. The diamond coatings are characterized by scanning electron microscopy and Raman spectroscopy. The graphitizing tendency due to cobalt in the tungsten carbide tools was found to be a limitation to improve adhesion of diamond films. The new tool substrates with nickel aluminide binder have been found to exhibit good adhesion and wear resistance. The implications of these results in advanced cutting tools are discussed.
Microstructure, electrical properties, and thermal stability of Al ohmic contacts to n-GaN
Authors: Smith L. L. , Davis R. F. , Kim M. J. , Carpenter R. W. , Huang Y.
Published: March 2008

As-deposited Al contacts were ohmic with a room-temperature contact resistivity of 8.6 × 10−5 Ω · cm2 on Ge-doped, highly n-type GaN (n = 5 × 1019 cm−3). They remained thermally stable to at least 500 °C, under flowing N2 at atmospheric pressure. The specific contact resistivities (ρc) calculated from TLM measurements on as-deposited Al layers were found to range from 8.6 × 10−5 Ω · cm2 at room temperature and 6.2 × 10−5 Ω · cm2 at 500 °C. Annealing treatments at 550 °C and 650 °C for 60 s each under flowing N2 resulted in an overall increase of contact resistivity. Cross-sectional, high-resolution electron microscopy (HREM) revealed that interfacial secondary phase formation occurred during high-temperature treatments, and coincided with the degradation of contact performance. Electron diffraction patterns from the particles revealed a cubic structure with lattice constant a = 0.784 nm, and faceting occurring on the {100} faces. Spectroscopic analysis via electron energy loss spectroscopy (EELS) revealed the presence of nitrogen and small amounts of oxygen in the Al layer, but no appreciable amounts of Ga. The results of microstructural and crystallographic characterization indicate that the new interfacial phase is a type of spinel Al nitride or Al oxynitride.
Effect of A-site vacancy order-disorder states on diffuse phase transition of the morphotropic phase boundary Pb1−xBaxNb2O6 ferroelectrics
Authors: Xiao Xiaoyue , Xu Yan , Zeng Zhigang , Gui Zhilun , Li Longtu , Zhang Xiaowen
Published: March 2008

The effect of A-site vacancy order-disorder states on diffuse phase transition (DPT) of tungsten bronze Pb1−xBaxNb2O6 (PBN) ferroelectrics has been investigated. The A-site vacancy disordered PBN ceramics exhibit notable variations of the Curie temperatures (i.e., the temperatures at the dielectric maximum permittivities) up to 12 °C in response to frequency changed from 0.1 KHz to 100 KHz. The largest frequency dispersion occurred at the morphotropic phase boundary of 1 − X = 0.63, along with the lowest Curie point. In contrast, the A-site vacancy ordered PBN ceramics present little frequency dispersion in the range of 2 °C from 0.1 KHz to 100 KHz. Dielectric constants of the disordered PBN ceramics were generally higher than those of the ordered ones. In comparison with the ordered PBN ceramics, the Curie points of the disordered ceramics were shifted from lower to higher temperature as the Pb2+ cation percentage was decreased; i.e., the Curie temperatures of the disordered PBN ceramics were lower than those of the ordered ones when 1 − X ≥ 0.70, but higher when 1 − X ≤ 0.65. These differences are suggested to inherently result from the A-site vacancy order-disorder states. The relationship between the A-site vacancy order-disorder states and the dielectric properties has also been confirmed with studies of thermal hysteresis.
Influence of microstructure on indentation and machining of dental glass-ceramics
Authors: Xu Hockin H. K. , Smith Douglas T. , Jahanmir Said
Published: March 2008

The influence of microstructure on the abrasive machining and indentation response for a series of dental glass-ceramics was characterized. The experimental materials prepared for this study contained crystalline mica platelets that ranged in diameter from about 1 to 15μm, while the volume fraction of mica remained essentially constant. Damage formation and material removal behavior were studied as a function of mica platelet size using Vickers indentation, Berkovich instrumented indentation, and abrasive machining. In the instrumented indentation experiments, the energy absorbed in indentation decreased with increasing platelet size when indentations of equal penetration depth are made in each material. To characterize the grinding response, the normal and tangential forces for each material were measured as a function of the depth of cut in surface grinding. The grinding forces and the specific grinding energy at fixed depths of cut decreased with increasing the mica platelet size following the same trend observed in the fixed displacement indentation tests. Since the same microfracture process was observed to occur in both indentation and grinding, the absorbed indentation energy is proposed as a quantity for predicting the machining response of these glass-ceramics.
Maximum heating rates for producing undistorted glassy carbon ware determined by wedge-shaped samples
Authors: Maleki Hossein , Holland Lawrence R. , Jenkins Gwyn M. , Zimmerman R. L. , Porter Wally
Published: March 2008

Polymeric carbon artifacts are particularly difficult to make in thick section. Heating rate, temperature, and sample thickness determine the outcome of carbonization of resin leading to a glassy polymeric carbon ware. Using wedge-shaped samples, we found the maximum thickness for various heating rates during gelling (300 K–360 K), curing (360 K–400 K), postcuring (400 K–500 K), and precarbonization (500 K–875 K). Excessive heating rate causes failure. In postcuring the critical heating rate varies inversely as the fifth power of thickness; in precarbonization this varies inversely as the third power of thickness. From thermogravimetric evidence we attribute such failure to low rates of diffusion of gaseous products of reactions occurring within the solid during pyrolysis. Mass spectrometry shows the main gaseous product is water vapor; some carboniferous gases are also evolved during precarbonization. We discuss a diffusion model applicable to any heat-treatment process in which volatile products are removed from solid bodies.
Crystallization behavior of Li1–5x Ta1+xO3 glasses synthesized from liquid precursors
Authors: Allemann J.A. , Xia Y. , Morriss R. E. , Wilkinson A. P. , Eckert H. , Speck J.S. , Levi C. G. , Lange F. F. , Anderson S.
Published: March 2008

The crystallization of amorphous oxides synthesized by pyrolytic decomposition of mixed Li and Ta 2-ethylhexanoates and alkoxides has been investigated. The study was motivated by thermodynamic considerations that, in the light of experience in other systems, suggest the potential for metastable extension of the LiTaO3 homogeneity range. Materials investigated are described by the general stoichiometry Li1–5xTa1+xO3 and include Li2O contents from 0 to 70 mol% (20.18 ≤ x ≤ 0.2). The samples were prepyrolyzed at 400 °C and subsequently crystallized by heat treatments in air at 550–700 °C for 0.1–100 h. The first product of crystallization for compositions from 30 to 65% Li2O is always the LiTaO3 phase. Extensive characterization by x-ray and neutron diffraction, as well as 7Li-NMR spectroscopy, revealed that this phase evolves with a structure and stoichiometry close to equilibrium. For Li+-deficient compositions, excess Ta5+ is rejected to the amorphous constituent during crystallization and eventually gives rise to the evolution of Ta2O5, with the LiTa3O8 phase suppressed in all cases. Similar observations were made for the Li+-rich compositions, but the evolving second phase is the equilibrium Li3TaO4. The absence of solubility extension in LiTaO3, which appears feasible from a thermodynamic viewpoint, is ascribed to the large differences in mobilities of the Li and Ta species in the parent amorphous oxide resulting from pyrolysis.
Precipitation of bcc nanocrystals in bulk Mg–Cu–Y amorphous alloys
Authors: Liu Wenshan , Johnson William L.
Published: March 2008

Coexistent amorphous and nanoscale bcc-Mg7Li3 phases were found in slowly quenched alloys of the Mg65–xLixCu25Y10 system containing 3 to 15 at. % Li. The crystallization behavior of these alloys has been studied. The grain size of the nanocrystalline bcc phase which is formed ranges from 2 to 20 nm. The volume fraction of nanocrystalline phases as well as the grain size of the nanocrystals increase as the Li composition increases. Transmission electron microscopy studies suggest that the alloy exhibits phase separation in the undercooled liquid state and that the nucleation and growth of the bcc-nanocrystals is related to the phase separation. Some characteristic thermal properties of the glassy phase are presented, and the composition dependence of Tg and Tx is discussed. It is concluded that the addition of a small amount of Li is essential for the production of a bcc nanocrystalline phase in the Mg–Li–Cu–Y system.
Bi-epitaxial grain boundaries in YBa2Cu3O7−x thin films prepared by pulsed laser deposition and pulsed organometallic beam epitaxy: Direct comparison of transport properties and grain boundary structure
Authors: Vuchic Boris , Merkle K. L. , Char K. , Buchholz D. B. , Chang R. P. H. , Marks L. D.
Published: March 2008

A set of 45° [001] bi-epitaxial YB2Cu3O7−x thin film grain boundaries was studied to compare the effects of the microstructure on transport properties. The grain boundaries were made using two different deposition techniques: pulsed laser deposition (PLD) and pulsed organometallic beam epitaxy (POMBE). The transport properties were highly dependent on the specific growth conditions used, resulting in both fully resistive and superconducting grain boundaries. Subsequent microstructural analysis of the measured boundaries showed that both types (superconducting and resistive) meandered on the length scale of hundreds of nanometers. The major structural difference between the boundaries was at the atomic scale where the resistive boundary had a 1 nm wide disordered region. The direct correlation of microstructure to transport properties demonstrates the importance of the atomic scale structure in the resulting transport behavior.
A study of a low copper dental amalgam by analytical transmission electron microscopy
Authors: Hooghan Tejpal Kaur , Pinizzotto Russell F. , Watkins John H. , Okabe Toru
Published: March 2008

Analytical transmission electron microscopy was used to study specimens of a low-Cu dental amalgam (Velvalloy), prepared using the “wedge technique.” Analysis confirmed that the microstructure consists of a Ag2Hg3(γ1)/HgSn7−9(γ2) matrix surrounding unreacted Ag3Sn(γ) particles. In addition a hitherto uncharacterized reaction layer of fine grains between Ag3Sn(γ) and Ag2Hg3(γ1) is a mixture of Ag3Sn(γ), Ag–Hg–Sn (β1), Ag2Hg3 (γ1), and occasionally Cu6Sn5 (η′). An Ag–Hg–Sn (β1) phase was clearly identified for the first time. Since Velvalloy is a simple commercial dental amalgam, it is a reasonable starting point for characterizing more complex dental amalgam microstructures.
Synthesis and characterization of a novel layered titanium phosphate
Authors: Bortun Anatoly I. , Bortun Lyudmila , Clearfield Abraham , Villa-García María A. , García José R. , Rodríguez Julio
Published: March 2008

A novel metastable layered titanium phosphate has been synthesized by the treatment of layered titanates (Na2Ti3O7 and Na4Ti9O20) with 1–2 M phosphoric acid solution at 120–150 °C. Based on the data of 31P MAS NMR and IR spectroscopy, x-ray powder diffraction, and thermal and elemental analysis, the formula Ti2O3(H2PO4)2 · 2H2O was assigned to the novel compound. The layered nature of the compound was confirmed from n-alkylamine intercalation and the ion exchange behavior toward alkali, alkaline earth, and some transition metal ions.
Magnetoelastic anisotropy distribution in glass-coated microwires
Authors: Velázquez J. , Vázquez M. , Zhukov A. P.
Published: March 2008

Amorphous microwires, obtained by the glass-coated melt-spinning method having diameters in the range of micrometers, can exhibit perfectly square (single and large Barkhausen jump) or quasi-anhysteretic hysteresis loops, depending on the easy magnetization direction determined by the intrinsic magnetoelastic anisotropy. The thermoelastic internal stressed frozen-in during the fabrication that model the domain structure are here calculated by considering the classical theory of elasticity. A complex stress distribution is obtained having magnitude of 103 MPa. Circular stresses turn out to be predominant, which arises from the composite nature of the microwire (metallic nucleus and insulating glass coating having different mechanical and thermal properties).
Sintering and properties of Li2O · Al2O3 · 4SiO2-borosilicate glass composites
Authors: Shyu Jiin-Jyh , Wang Ching-Tang
Published: March 2008

Sintering, glass crystallization, microstructure, and the resulting properties of spodumene-borosilicate glass composites were investigated. Densities >90% could be obtained for samples sintered below 1000 °C. Samples that contained more low-viscosity glass densified at lower temperatures, and significant density reduction was observed at higher temperatures. Samples that contained high-viscosity glass densified only at higher temperatures. When glasses of different viscosity were added, the densification of the composites was improved. There was interdiffusion between spodumene and glass. Cristobalite crystallized from the pure glasses. Addition of spodumene changed the major phase crystallized to anorthite or α-quartz as a result of dissolution of spodumene into glass. Composites that contained glass of higher silica content showed more crystallization. As sintering temperatures increased, the amount of crystallization decreased, due to dissolution of glass into spodumene. The spodumene particles showed angular shape with smooth and straight sides. The spodumene-glass composites showed a dielectric constant in the range of 5–6, a loss tangent generally <1%, and a CTE value in the range of 2–5.6 × 10–6 K–1. Codoping of glasses with different viscosity effectively improved the densification and properties of the composites.
Fracture behavior of Al2O3/SiC-platelet composites
Authors: Belmonte M. , Moya J. S. , Miranzo P. , Nguyen D. , Dubois J. , Fantozzi G.
Published: March 2008

Mechanical behavior of hot-pressed SiC platelet reinforced alumina composites has been analyzed as a function of SiC platelet content for two different alumina matrix powders. Fracture toughness and flexural strength at temperatures ranging from 25 to 1200 °C, R-curve behavior, and thermal shock resistance have been determined. Small differences in the impurity content of the starting Al2O3 powders strongly determine the microstructure and the mechanical behavior of Al2O3/SiC-platelet composites. Low alkali content alumina led to composites with large matrix grain size which presented spontaneous microcracking. At high temperature, a high viscosity liquid phase is formed that shields cracks enhancing mechanical properties and R-curve behavior. A small amount of impurities reduced Al2O3 matrix grain size and avoided spontaneous microcracking. Enhanced fracture toughness (up to 30%) at room temperature, R-curve behavior, and thermal shock resistance were achieved for these materials.
Metastable δ-Bi12SiO20 and its effect on the quality of grown single crystals of γ-Bi12SiO20
Authors: Fu Senlin , Ozoe Hiroyuki
Published: March 2008

Metastable δ-Bi12SiO20 may crystallize from the overheated Bi12SiO20 melt and transform into stable γ-Bi12SiO20 at about 569.5 °C during the subsequent slow cooling process. The transition δ-Bi12SiO20 → γ-Bi12SiO20 is irreversible and the γ-Bi12SiO20 is stable up to the melting temperature. By quenching the Bi12SiO20 melt, pure δ-Bi12SiO20 can be obtained at room temperature. The quenched δ-Bi12SiO20 crystal is nontransparent and has a space group of Fm3m (225) and a lattice constant of 55.417 Å at 20 °C. The quenched metastable δ-Bi12SiO20 can transform into pure γ-Bi12SiO20 at 382.5–386.1 °C with an exothermic heat of 31.68–32.38 J/g. The transition-produced δ-Bi12SiO20 crystal is still nontransparent and has a large lattice distortion. The transition δ-Bi12SiO20 → γ-Bi12SiO20 causes about 6% volume contraction, which may result in cracking of the grown crystal. By controlling the growth parameters, this transition can be effectively avoided.
Preparation of zirconia thin films by metalorganic chemical vapor deposition using ultrasonic nebulization
Authors: Kim Dong-Young , Lee Choon-Ho , Park Soon Ja
Published: March 2008

Zirconia (ZrO2) thin films were prepared by metalorganic chemical vapor deposition (MOCVD) using ultrasonic nebulization with new source materials, Zr(OBu)4, Zr(OBu)3(acac), Zr(OBu)2(acac)2, and Zr(OBu) (acac)3. This process is a simple and economic method to prepare oxide thin films. Zr(OBu)4 was successfully reacted with acetylacetone at a molar ratio of 1: 3. Polycrystalline thin films were deposited at a substrate temperature range from 300 to 550 °C. The substitution of alkoxy radicals by acetylacetone made the deposition rate higher and insensitive to substrate temperature. The films deposited below 450 °C mostly had a monoclinic structure, and those deposited above 450 °C had a tetragonal structure. The measured optical energy band gap of zirconia film was 5.32 eV.
Microstructure and ferroelectric properties of fine-grained BaxSr1−xTiO3 thin films prepared by metalorganic decomposition
Authors: Mohammed Majed S. , Naik Ratna , Mantese Joseph V. , Schubring Norman W. , Micheli Adolph L. , Catalan Antonio B.
Published: March 2008

Thin films of BaxSr1−xTiO3 (x = 0.7, 0.8, 0.9, and 1.0) were prepared by metalorganic decomposition (MOD). The relative permittivity, dissipation, polarization, resistivity, and grain size of these films were studied as a function of composition and temperature. Ferroelectric hysteresis loops were observed for all values of x and were found to be independent of measurement temperature though strongly dependent upon grain size.
Thermal plasma treatment of titanium carbide powders: Part I. Numerical analysis of powder behavior in argon-hydrogen and argon-nitrogen radio frequency plasmas
Authors: Watanabe Takayuki , Kanzawa Atsushi , Ishigaki Takamasa , Moriyoshi Yusuke
Published: March 2008

Modeling of TiC powder behavior in Ar–H2 and Ar–N2 RF thermal plasmas has been performed as well as the numerical analysis of the plasma fields to investigate the plasma/powders interaction. The heat transfer rate from the plasma to the powders decreases with increasing the powder feed rate and with decreasing the plasma pressure, because of the significant local cooling owing to the presence of the injected powders. These results agree fairly well with the experimental results of our following paper. The modeling herein gives guidance for the rational design of new material processing using thermal plasmas.
Crystal growth and electrical properties of Li2B4O7
Authors: Byrappa K. , Rajeev V. , Hanumesh V. J. , Kulkarni A. R. , Kulkarni A.B.
Published: March 2008

Growth of Li2B4O7 crystals has been carried out under hydrothermal conditions at relatively low temperature and pressure conditions (T = 250 °C, P = 100 bars). A systematic study of electrical measurements has been carried out within a wide range of internal frequency and temperature. The corresponding impedance, Arrhenius, and Bode plots are given.
Optical fiber-drawing temperature of fluorogallate glasses
Authors: Suriñach S. , Illekova E. , Zhang G. , Poulain M. , Baró M.D.
Published: March 2008

The thermal properties and the crystallization behavior of fluorogallate-based glasses were analyzed. The kinetic nature of the glass transition was used to determine the temperature dependence of the viscosity and from it an estimation of the appropriate drawing temperature for an optical fiber was established. The crystallization kinetics were studied by using both isothermal and continuous heating regimes. The temperature range for nucleation was evaluated and for samples previously nucleated the activation energy of the growth process was found. The results were used to estimate the empirical nucleation and crystal growth rates from which the time-temperature-transformation curves and the temperature-heating rate-transformation diagrams were constructed. The results obtained agree with experimental data and are discussed in the light of minimizing the volume of crystals formed during fiber drawing.