bluuebunny/crossref_metadata_2025 huggingface dataset:
The design of three-dimensional turbine blades combined with profiled endwalls
Authors: Bagshaw D A , Ingram G L , Gregory-Smith D G , Stokes M R , Harvey N W
Published: March 2008

This paper describes a novel design for reducing secondary flow in turbines. The design builds on previous work on non-axisymmetric profiled endwalls by combining them with three-dimensional blade design. Profiled endwalls have been shown to effectively reduce secondary flow but have often been used as a ‘retrofit’ application where the blade design is left unchanged. In the current paper reverse compound lean is used to prepare the blade row for the application of profiled endwalls. Computational fluid dynamic predictions ofthe expected performance show benefits over and above those of applying profiled endwalls to the blade row alone. The paper describes the design of the novel geometry for the so-called ‘Durham Cascade’ and gives predictions of the expected performance.
An experimental study of three-dimensional turbine blades combined with profiled endwalls
Authors: Bagshaw D A , Ingram G L , Gregory-Smith D G , Stokes M R
Published: March 2008

This paper presents a detailed series of measurements on a novel design for reducing secondary flow in a linear cascade. The design of this geometry, which features profiled endwalls and three-dimensional blade shaping was discussed in a companion paper [1]. This paper presents the results of static pressure measurements on the blade surface, pneumatic pressure probe traverses, and surface oil flow visualization in order to build a comprehensive picture of the geometry's performance and function. Although the interactions between blade shaping and profiled endwalls are complex the experimental results show benefits over applying profiled endwalls alone.
Thermomechanical exergy and thermoeconomic analysis of geothermal district heating systems
Authors: Ozgener L , Ozgener O
Published: March 2008

The current paper presents the thermomechanical exergy and thermoeconomic analysis of geothermal district heating systems (GDHSs) in Turkey. The case studies cover the actual system data taken from the systems in Afyon, Gonen, and Salihli GDHSs, Turkey. General energy and exergy analysis of the GDHSs are introduced. Then the analysis applied to these GDHSs using actual thermodynamic data for their performance evaluations in terms of energy and exergy efficiencies are presented. Besides, thermoeconomic evaluations of GDHSs are given in tables.
Recent advances in hearing restoration
Authors: Kulkarni Kunal , Hartley Douglas EH
Published: March 2008

Summary

This review is based on Pubmed, Medline and Internet literature searches, supplemented by knowledge from textbooks, conference presentations, and personal communications with experts in the field of hearing restoration and patients. We have not specifically selected a time limit for our literature searches; however, the majority are articles from the past 5 years.
A Metaheuristic Approach for the Vertex Coloring Problem
Authors: Malaguti Enrico , Monaci Michele , Toth Paolo
Published: March 2008

Given an undirected graph G = (V, E), the vertex coloring problem (VCP) requires to assign a color to each vertex in such a way that colors on adjacent vertices are different and the number of colors used is minimized. In this paper, we propose a metaheuristic approach for VCP that performs two phases: the first phase is based on an evolutionary algorithm, whereas the second one is a postoptimization phase based on the set covering formulation of the problem. Computational results on a set of DIMACS instances show that the overall algorithm is able to produce high-quality solutions in a reasonable amount of time. For four instances, the proposed algorithm is able to improve the best-known solution while for almost all the remaining instances, it finds the best-known solution in the literature.
Daten für die Zukunft – Das BMBF-Projekt Kooperativer Aufbau eines Langzeitarchivs digitaler Informationen (kopal) und seine Hintergründe
Authors: Altenhöner Reinhard
Published: March 2008

Seit Sommer 2004 führt Die Deutsche Bibliothek zusammen mit mehreren Partnern mit kopal ein vom Bundesministerium für Bildung und Forschung finanziertes Projekt zur Etablierung einer technischen Plattform für die Langzeitarchivierung in Deutschland durch. Die Tatsache, dass das Projekt mittlerweile in die eigentliche Entwicklungs- und Umsetzungsphase eingetreten ist, gibt Anlass, das Vorhaben und den aktuell erreichten Stand in größerem Zusammenhang vorzustellen.
Sciences of complexity and language origins: an alternative to natural selection
Authors: Longa Víctor M
Published: March 2008

Natural selection is claimed to be the only way to explain complex design. The same assumption has also been held for language. However, sciences of complexity have shown, from a wide range of domains, the existence of a clear alternative: self-organisation, spontaneous patterns of order arising from chaos. According to this view, design derives from internal factors (dynamic interaction of the elements within the system) rather than from adaptation to the environment by means of selection. This paper aims to apply sciences of complexity to language origins; it shows that preexisting and well established ideas can be rethought according to such a view. The main objective of the paper is to illustrate the new and promising horizons that complexity could open as regards the origins of the most specific property of human beings.
Applying C1601-06 “Standard Test Method for Field Determination of Water Penetration of Masonry Wall Surfaces” in Practice
Authors: Dalrymple Gerald A. , Rhett Whitlock A.
Published: March 2008

Water permeance of exterior masonry wall systems drives masonry restoration and repair design decisions from selection of flashing replacement to pointing to application of water repellents. ASTM C1601 was first issued in August 2004 and has not been used extensively in service by professionals to evaluate masonry wall surfaces. ASTM C1601 provides a standard method of measuring water permeance that can be used to evaluate existing wall surfaces prior to specifying repair methods and as a tool to evaluate the overall effectiveness of repair methods so that efficient repair options can be selected. This paper reviews the requirements of the test method, application of the test method and interpretation of test results. Historical test data are presented that illustrate use of the test method to evaluate wall systems and expected range of test results for existing and repaired wall systems that can be used to select appropriate repair procedures.
Film Culture in Rome
Authors: Forgacs David
Published: March 2008

This essay describes a number of facilities and institutions in Rome, including the film festival, film school, exhibition circuit, and key production center Cinecittà.
Public Disclosure in Research with Exception from Informed Consent: The Use of Survey Methods to Assess its Effectiveness
Authors: Jacoby Liva H. , Young Barry , Watt James
Published: March 2008

In clinical trials with exception from informed consent, the Final Rule stipulates that investigators inform and consult with the community. A random-digit-dialing survey of 200 individuals assessed the effectiveness of public disclosure via press releases, notices in local newspapers, local radio and television stations and the host hospital's website, as well as a series of community meetings regarding a pending clinical trial of this kind. Results showed a 10% awareness level of the public trial, which is higher than surveys using convenience samples. Understanding of the nature of the trial was generally poor, while opinions about participating in this type of research were more favorable among individuals aware of the trial. Our findings suggest that adherence to the intent of the Final Rule is dependent on uniform guidelines for what constitute effective public disclosure methods and adequate community awareness and understanding and the use of rigorous sampling methods for evaluation.
The District Six Museum: An Ordinary People's Place
Authors: LAYNE VALMONT
Published: March 2008

This article describes the founding and work of the District Six Museum. Under the apartheid system, District Six was declared a white-only area. Many residents were forcibly removed, and almost all of the buildings were bulldozed. The District Six Museum was launched in 1994 to keep alive the memories of District Six and displaced people everywhere. It is a space where the forgotten understandings of the past are resuscitated, and where different interpretations of that past are facilitated. The museum also assists in the reconstitution of the community of District Six and Cape Town.
Low temperature synthesis of ultrafine Pb(Zr, Ti)O3 powder by sol-gel combustion
Authors: Schäfer J. , Sigmund W. , Roy S. , Aldinger F.
Published: March 2008

Lead zirconate titanate powders are derived from a novel aqueous-based citrate-nitrate/oxynitrate sol-gel combustion process. Aqueous solutions of metal nitrates or oxynitrates are transformed into gels with citric acid under heating. The received gels undergo a self-propagating combustion reaction on heating to 180 °C and subsequently yield voluminous ashes. These ashes form single phase perovskite Pb(Zr0.53Ti0.47)O3 powder with a specific surface area of 8 m2/g upon calcination at 550 °C. The ashes show a homogeneous distribution of lead, zirconium, and titanium ions which guarantees short diffusion paths in solid state formation of PZT perovskite. The redox behavior of the gels was studied with the help of DTA experiments. Powders are characterized in terms of XRD, SEM, and EDX analysis.
Crystallization of hafnia and zirconia during the pyrolysis of acetate gels
Authors: Yashima Masatomo , Kato Taka-aki , Kakihana Masato , Gulgun Mehmet Ali , Matsuo Yohtaro , Yoshimura Masahiro
Published: March 2008

Hafnia and zirconia gels were prepared by drying hafnyl or zirconyl acetate solutions. Hafnia and zirconia gels contain both hydroxyl group and bidentate acetates which are directly bonded to the metal ions. Thermal decomposition and crystallization behavior of the gels were investigated through XRD, FT-IR, and TEM. Hafnium-containing gels crystallized directly into stable monoclinic hafnia around 500–540 °C, while zirconium-containing gels first formed metastable tetragonal zirconia around 450 °C. The dissimilar crystallization behavior of the gels into metastable, tetragonal zirconia or into stable, monoclinic hafnia can be explained through the difference in free-energy changes of the tetragonal-to-monoclinic phase transformation.
Processing and characterization of lead magnesium tantalate ceramics
Authors: Akbas Mehmet A. , Davies Peter K.
Published: March 2008

Using a processing route that employed platinum crucibles, single phase ceramics of Pb(Mg1/3Ta2/3)O3 (PMT) relaxor ferroelectrics were prepared with densities greater than 95% of their theoretical value. The improvements in the sintering characteristics of this system that result from this route were reflected by the dielectric properties, at 182 K, which are similar to those reported for single crystal PMT. Contrast originating from nanosized polar clusters was evident in dark-field TEM images collected from the PMT ceramics at room temperature and showed little change upon cooling through the permittivity maximum. The electron diffraction patterns contained weak superlattice reflections at (h ± 1/2, k ± 1/2, l ± 1/2) that originate from a 1: 1 ordering of the B-site cations. High resolution imaging indicated that the length scale of the chemical ordering in PMT is essentially identical to niobate relaxors such as PMN, with the 1–2 nm ordered domains being surrounded by a disordered matrix.
Investigation of a new fracture mechanics specimen for thin film adhesion measurement
Authors: de Boer Maarten P. , Kriese Michael , Gerberich William W.
Published: March 2008

We have investigated mechanical probing of a precracked fine line structure as a new type of thin film fracture mechanics specimen. An idealized mechanics analysis is first presented. Experimentally, two types of precracks are formed. A thin carbon layer to which other layers weakly adhere creates a “processed precrack” by integrated circuit processing techniques. An “indented processed precrack” is formed by precision alignment of a sharp microwedge. The processed precrack is found to reduce the critical tangential load by 50% from a non-precracked line, while the indented processed precrack lowers the load by 200%. From this, a reasonable value of adhesion may be directly calculated. Crack path behavior is observed to depend on strength of the interface. In the case of a weak interface, the crack remains in the interface as it extends. For a strong interface, it kinks into the substrate if the crack is initially short, but remains in the interface if it is initially long. Given the experimental evidence, the mechanics are slightly modified to quantitatively model the experimental data.
Effect of Nd content on the magnetic properties and crystallographic alignment of Fe–Nd–B–Al sintered magnets
Authors: Kaszuwara W. , Leonowicz M. , Davies H. A.
Published: March 2008

The magnetic properties and crystallographic alignment for Fe–Nd–B–Al magnets having different Nd contents were studied. It was found that higher Nd concentration (above 18 at. %) resulted in deterioration of the alignment. Also, extended ball milling of the powder particles resulted in poorer alignment of the grains in the final sintered magnet. This behavior was attributed to the cold welding of the small particles of the Fe14Nd2B phase by a mechanically soft Nd-rich phase in the course of ball milling.
Does the shear-lag model apply to random fiber networks?
Authors: Räisänen V. I. , Alava M. J. , Niskanen K. J. , Nieminen R. M.
Published: March 2008

The shear-lag type model due to Cox (Br. J. Appl. Phys. 3, 72 (1952) is widely used to calculate the deformation properties of fibrous materials such as short fiber composites and random fiber networks. We compare the shear-lag stress transfer mechanism with numerical simulations at small, linearly elastic strains and conclude that the model does not apply to random fiber networks. Most of the axial stress is transferred directly from fiber to fiber rather than through intermediate shear-loaded segments as assumed in the Cox model. The implications for the elastic modulus and strength of random fiber networks are discussed.
Compensation phenomena in oil-resin mixtures: A new dielectric approach to percolative processes
Authors: Pagés O. , Lamure A. , Lacabanne C. , Odlyha M. , Craig D.
Published: March 2008

The methods of thermally stimulated currents (TSC) together with low frequency dielectric spectroscopy (LFDS) are combined for the first time to study percolation phenomena. These take place within oil-resin mixtures which constitute conductor/insulator-like composite systems. Each of these techniques is shown to describe selectively one of two different kinds of relaxation processes in the oil component: first, anelastic dipolar movements and second, the circulation of free charges. The separate qualitative interpretations of the combined TSC/LFDS experiments lead to convergent estimations of the percolation thresholds of the two basic materials in oil-resin mixtures. The latter appear as critical concentrations for which the dielectric relaxation processes either comply suddenly with compensation laws or pre-existing compensation phenomena change in nature.
Synthesis and properties of Tl–Ba–Ca–Cu–O superconductors
Authors: Siegal M. P. , Venturini E. L. , Morosin B. , Aselage T. L.
Published: March 2008

We review the synthesis methods and properties of single crystal, powder, and thin film TlBaCaCuO high-temperature superconducting (Tl-HTS) materials. With transition temperatures ≥ 100 K for several compounds, Tl-HTS materials present real opportunities for applications above 77 K. Experiments using (1) single crystals: determined precise structural parameters and identified the complex Tl1+–Tl3+ equilibrium model; (2) powders: studied the complex thermodynamic phase diagram; and (3) epitaxial films: studied fundamental properties such as electron pair symmetry and the effect of controlled extrinsic defects on flux pinning strength, as well as providing the large-area surfaces required for device applications.
Fabrication of NdBCO single crystal oxide superconductor with enhanced superconductive properties
Authors: Kambara M. , Yao X. , Nakamura M. , Shiohara Y. , Umeda T.
Published: March 2008

Nd1+xBa2−xCu3O6+d (Nd123) single crystals have been successfully grown by the top-seeded solution-growth method. Compositions of Nd123 could be controlled by applying two different methods: control of the oxygen partial pressure of the atmosphere and control of the liquid composition in air. The critical temperatures of Nd123 obtained by these two methods were 96 K (oxygen control) and 95 K (liquid composition control), respectively. The relationship between the peak effect in the Jc-H curve and heat treatment was investigated. The peak effect was found not to be an intrinsic property of Nd123; consequently it could be controlled by heat treatment.
Effect of initial composition on distribution of RE211 (422) particles in RE123 superconductors
Authors: Kambara M. , Watanabe Y. , Miyake K. , Endo A. , Murata K. , Shiohara Y. , Umeda T.
Published: March 2008

Microstructure in melt-textured bulk RE1Ba2Cu3O6+d crystals (RE123; RE = Sm, Nd) was investigated, changing the initial composition from the tie-line composition of RE123–Sm2Ba1Cu1O5 (Sm211)/Nd4Ba2Cu2O10 (Nd422) to the Ba-enriched side. It was found that the Sm211/Nd422 particle size decreased in the liquid with increasing the Ba/Cu ratio of the initial composition, and this tendency was also found in the grown Sm123 crystals. Composition of the Sm123 grown crystal could be controlled by selecting the Ba-enriched initial composition to obtain an almost stoichiometric compound, which resulted in higher Tc values. Furthermore, the Jc values also increased under low magnetic fields due to the significant decrease of Sm211 particle size. Therefore, changing the initial composition toward the Ba-enriched side was found to be a new process to enhance both Jc and Tc values simultaneously.
Doping high Tc superconductors with oxygen and metallic atoms: A molecular dynamics study
Authors: Stoll Erich , Stern Christian , Singer Johannes , Stucki Peter
Published: March 2008

Using classical molecular dynamics based on Lennard–Jones-like potentials, a mechanically stable YBa2Cu3O7 high Tc superconductor structure is generated. This process is controlled via interactive computer graphics. After doping atoms into or removing atoms from the sample using a recently implemented picking mechanism, the lattice oscillation energy is annihilated with a simulated annealing procedure. The remaining minimum ground state energy allows marking of the preferred doping location. Information on the doping mechanism is important because the magnetic and superconducting properties of these compounds depend very strongly on their oxygen content.
Biaxial alignment control of YBa2Cu3O7−x films on random Ni-based alloy with textured yttrium stabilized-zirconia films formed by ion-beam-assisted deposition
Authors: Iijima Y. , Hosaka M. , Tanabe N. , Sadakata N. , Saitoh T. , Kohno O. , Takeda K.
Published: March 2008

Biaxially aligned YBa2Cu3O7−x (YBCO) films were fabricated on random Ni-based alloy tapes with yttrium stabilized-zirconia (YSZ) buffer layers deposited by ion-beam-assisted deposition (IBAD). Ar+ ion bombardment was found to have two significant effects on the crystalline structure of the YSZ buffer layers: to align a [100] axis with the substrate normal and a [111] axis with the bombarding beam axis. The resulting YSZ films were biaxially aligned on the random polycrystalline tapes, and the azimuthal distribution of the a- and b-axes of YBCO films on the top of the YSZ films was restricted to 10° FWHM. A critical current density (Jc) of 1.13 × 106 A/cm2 (77 K, 0 T) was obtained, and 1.1 × 105 A/cm2 was maintained at 5 T (77 K, B⊥c). The existence of both intrinsic and extrinsic pinning properties was clearly observed in the angular dependence of Jc with B⊥I. The longitudinal field effect on Jc was clearly observed, which indicated straight transport currents. This is evidence for strongly coupled current paths that demonstrate the bulk pinning properties of YBCO.
Nanostructured high-temperature superconductors: Creation of strong-pinning columnar defects in nanorod/superconductor composites
Authors: Yang Peidong , Lieber Charles M.
Published: March 2008

A chemical approach to the formation of columnar defects involving the growth and incorporation of MgO nanorods into high temperature superconductors (HTS's) has been developed. MgO nanorods were incorporated into Bi2Sr2CaCu2Oz, Bi2Sr2Ca2Cu3Oz, and Tl2Ba2Ca2Cu3Oz superconductors at areal densities up to 2 × 1010/cm2. Microstructural analyses of the composites demonstrate that the MgO nanorods create a columnar defect structure in the HTS matrices, form a compositionally sharp interface with the matrix, and self-organize into orientations perpendicular and parallel to the copper oxide planes. Measurements of the critical current density demonstrate significant enhancements in the MgO nanorod/HTS composites at elevated temperatures and magnetic fields compared with reference samples.
Connectivity and flux pinning improvements in Ag-clad BSCCO-2223 tapes produced by changes in the cooling rate
Authors: Parrell J. A. , Larbalestier D. C. , Riley G. N. , Li Q. , Carter W. L. , Parrella R. D. , Teplitsky M.
Published: March 2008

The rate at which Ag-clad (Bi, Pb)2Sr2Ca2Cu3Ox tapes are cooled from their final reaction heat treatment influences both the intergranular connectivity and intragranular flux pinning strength of the polycrystalline filaments. As the cooling rate from 825 °C to 730 °C in 7.5% O2 was decreased over a range of 5 °C/min to 0.005 °C/min, Jc (77 K, 0 T) increased from ∼8 to ∼24 kA/cm2, and the irreversibility field increased from, ∼120 to, ∼200 mT. The Jc (4.2 K, 0 T) increased in a similar fashion. Cooling slowly also sharpened the critical temperature transition and increased the critical onset temperature from 107 K to 109 K. These improvements in the superconducting properties occurred despite partial decomposition of the (Bi, Pb)2Sr2Ca2Cu3Ox phase into non-superconducting impurity phases during the slow cooling. A microstructural basis for these multiple effects is described.
Crystallization behavior and microstructure of lithium-calcium aluminogermanate glasses
Authors: Wang Moo-Chin
Published: March 2008

The crystallization behavior and microstructure of lithium-calcium aluminogermanate (LCAG) glasses have been studied by using differential thermal analysis (DTA), x-ray diffraction (XRD), scanning electron microscopy (SEM), scanning transmission electron microscopy (STEM), and electron diffraction (ED). Uniform crystallization of the LCAG glass was found to result from two stages of the heating process. The kinetics of crystallization of the LCAG glasses was studied by DTA using the nonisothermal method. The activation energy for 3CaO · Al2O3 · 3GeO2 crystal growth was 693 kJ/mol. The precipitated crystals determined by XRD analysis were mainly 3CaO · Al2O3 · 3GeO2, and minor phases of 2CaO · Al2O3 · GeO2 and Li2O · Al2O3 · 2GeO2. Morphology and microstructure of the glasses after heat treatment determined by SEM and STEM techniques are presented. Crystallization starts at the surface of the glass sample and then proceeds toward the interior of glass matrix. The morphology of 2CaO · Al2O3 · GeO2 is that of a subangular bell-shaped single crystal growing in a preferred orientation through the segregated phase matrix of fine dispersion of 3CaO · Al2O3 · 3GeO2 crystals. The Li2O · Al2O3 · 2GeO2 phase grows anisotropically in the fine fibrillar morphology and parallel to the [331].
Investigation of Al–Pb nanocomposites synthesized by nonequilibrium processes
Authors: Sheng H. W. , Zhou F. , .Hu Z. Q , Lu K.
Published: March 2008

Two nonequilibrium processes (melt-spinning and ball-milling) were successfully employed to synthesize Al1−xPbx(x= 5, 10, 20, 30 wt. %) nanocomposites with distinct microstructures. In the melt-spun (MS) Al–Pb alloys, the nanometer-sized Pb particles are uniformly distributed in the micrometer-grained Al matrix and have an orientational relationship with the matrix, while in the ball-milled (BM) samples, both Pb and Al components are refined with prolonged milling time, forming nanocomposites with Pb particles homogeneously dispersed into the Al matrix. The minimum particle size of Pb in the milled samples linearly increases with the Pb content. The microhardness of the BM Al–Pb samples is much larger than that of the MS samples, which mainly results from strengthening effects of the nanometer scale Al grains following the Hall–Petch relationship. The microhardness for both BM and MS Al–Pb samples varies with the Pb content, and maximum hardness for both samples exists when Pb content is about 5 wt. %, indicating that small amounts of Pb, in the form of nanoparticles, may strengthen the Al matrix.
Influence of Fe impurity in nitridation of Si + B4C green compact
Authors: Liu Dangrong R. , Shinozaki Samuel , Miyata Motoyuki , Yasutomi Yoshiyuki
Published: March 2008

The addition of B4C powder retarded the nitridation of the silicon powder green body by the formation of a borosilicate layer in interfaces between Si grains. The viscous layers hindered the SiO formation and the Si and N diffusion. Despite the presence of borosilicate layers, the Fe impurity in the green body still promoted the Si nitridation process by the formation of fluid iron silicide and the promotion of the B4C conversion to BN in gaps or holes in the viscous borosilicate layers. The addition of 5% H2 in the N2 atmosphere accelerated the Si + B4C nitridation, where the hydrogen acted as an oxygen getter, thus reducing the amount of glassy borosilicate in the interface.
Characterization of polycrystalline silicon carbide films grown by atmospheric pressure chemical vapor deposition on polycrystalline silicon
Authors: Zorman Christian A. , Roy Shuvo , Wu Chien-Hung , Fleischman Aaron J. , Mehregany Mehran
Published: March 2008

X-ray diffraction, transmission electron microscopy, and Rutherford backscattering spectroscopy were used to characterize the microstructure of polycrystalline SiC films grown on as-deposited and annealed polysilicon substrates. For both substrate types, the texture of the SiC films resembles the polysilicon at the onset of SiC growth. During the high temperature deposition process, the as-deposited polysilicon recrystallizes without influencing the crystallinity of the overlying SiC. An investigation of the SiC/polysilicon interface reveals that a heteroepitaxial relationship exists between polysilicon and SiC grains. From this study, a method to control the orientation of highly textured polycrystalline SiC films has been developed.
Nitride formation in iron after nitrogen implantation in a nickel top layer
Authors: Inia D. K. , Tichelaar F. D. , Arnoldbik W. M. , Vredenberg A. M. , Boerma D. O.
Published: March 2008

Nitrogen was introduced in an iron layer underneath a top layer of nickel. This was done by ion implantation of N into the Ni layer at a temperature of 200 °C. During implantation and subsequent anneals at 250 and 300 °C, N diffuses from the Ni layer into the Fe layer because of a larger affinity of Fe for N than of Ni for N. The concentration depth profiles of N in the Ni/Fe bilayers, as recorded with the nuclear reaction analysis technique, show at the highest implantation dose a peak below the Ni/Fe interface. From structural analysis techniques (x-ray diffraction and cross-sectional transmission electron microscopy) it was observed that this peak is due to the presence of an ε–Fe3−xN layer below the Ni/Fe interface. It is thus shown that ε –nitride can be formed in Fe at such low temperatures in the absence of radiation damage.
A study of piezoelectric orthorhombic Ta2O5
Authors: Jooste B. R. , Viljoen H. J.
Published: March 2008

In 1985 it was first reported that monoclinic Ta2O5 has piezoelectric properties comparable to ZnO. In this work we report on the deposition, characterization, and qualitative assessment of the piezoelectric behavior of orthorhombic Ta2O5. Reactive magnetron sputtering was used to deposit thin films of Ta2O5 onto substrates of 316L stainless steel. Without substrate heating the crystallinity was poor. A rapid thermal anneal improved the crystallinity. The orthorhombic phase was dominantly present on all substrates. The piezoelectric property was qualitatively assessed, including a high temperature test at 650 °C.
Thermal transport due to material and gas flow in a furnace for drawing an optical fiber
Authors: Roy Choudhury S. , Jaluria Y.
Published: March 2008

The transport processes involved in the neck-down region for optical fiber drawing are numerically investigated. In this manufacturing process, a moving glass rod is heated in a furnace containing an inert gas environment and drawn into a thin optical fiber. The conjugate problem is solved considering both radiation and convection, with focus on the latter. Two different flow configurations, involving inert gas flow in the same as well as in the opposite direction as the moving preform/fiber, are considered in this study. A coordinate transformation is used to change the complicated computational domains in the gas and the fiber to cylindrical ones. The transport in the fiber is coupled with that in the gas through the boundary conditions. The radiative thermal transport is calculated using an enclosure model developed in an earlier study. The numerical results on convective flow and transport are validated by comparing with results available in the literaturefor simpler configurations. The effects of several important parameters such as fiber draw speed, inert gas velocity, furnace dimensions, and gas properties on the flow and temperature distributions are investigated. For the aiding flow case, in which the inert gases flow in the same direction as the fiber, heat transfer to the fiber increases as the gas velocity increases. For opposing flow, a recirculating region appears in the gas, close to the moving fiber surface, causing reduction in heat transfer as compared to the aiding case. The thickness of this recirculating zone decreases with increasing inert gas velocity. Radiation is found to be the dominant mode of heat transfer in the overall heating of the preform/fiber, with nitrogen as the inert gas. However, near the edges of the furnace, radiation heat transfer is relatively small and convection becomes very important. Also, the convective transfer rate is relatively large near the flow entrance because of the large temperature difference between the gas and the fiber. However, away from the entrance, the gas heats up and the temperature difference relative to the fiber decreases, resulting in a smaller convective heat transfer rate. The relevance of the results to various aspects of the fiber-drawing process is discussed.
The correlation between τɛ and the tolerance factor in (Sr, Ca) (Ti, Zr)O3 microwave dielectric ceramics
Authors: Cheon Chae-Il , Kim Jeong-Seog , Lee Hyeung-Gyu
Published: March 2008

Microwave dielectric properties and the relationship between the temperature coefficient of the dielectric constant (τ ɛ) and the tolerance factor were investigated in (Sr0.2Ca0.8) (Ti1–xZrx)O3 ceramics. The τɛ increased linearly as the tolerance factor decreased from 0.984 to 0.929 in the whole composition range of the (Sr0.2Ca0.8) (Ti1–xZrx)O3 solid solution. At the composition of (Sr0.2Ca0.8) (Ti0.04Zr0.96)O3, the dielectric constant was 34 and Q · f was 10,938 GHz and the temperature coefficient of the resonance frequency (τɛ) was supposed to be near zero.
Effects of electrochemical hydrogen charging on lead-based relaxor ferroelectric multilayer ceramic capacitors
Authors: Chen Wanping , Li Longtu , Wang Yu , Gui Zhilun
Published: March 2008

Lead-based relaxor ferroelectric multilayer ceramic capacitors (MLC's) were placed in 0.05 M NaOH solution to evolve hydrogen on their silver termination electrode by electrolysis of water. After this treatment, the MLC's failed as their insulation resistance was greatly decreased, their dielectric loss was considerably increased, and their capacitance was obviously decreased. By annealing in air at 650 °C for 30 min, the properties of the MLC's were restored. It is proposed that electrochemically generated hydrogen atoms can diffuse into the ceramic body of MLC's and undergo reduction to it, which may be one of the reasons for the negative influence of electroplating on lead-based relaxor ferroelectric MLC's.
Correcting errors in the theory for mirage-effect measurements
Authors: Josell D. , Gonzalez E. J. , White G. S.
Published: March 2008

Errors are noted in two publications on the theory for Mirage-effect measurements of the thermal diffusivity of materials. The works include theory for interpreting Mirage experiments on homogeneous samples mounted on a support with ambient (typically air) above and theory for interpreting Mirage experiments on coated substrates with ambient both above and below.
Structure of Pd–Te precipitates in a simulated high-level nuclear waste glass
Authors: Galoisy L. , Calas G. , Morin G. , Pugnet S. , Fillet C.
Published: March 2008

Structural and bonding characteristics of simplified (Pd, Te) precipitates have been determined in a simulated nuclear French glass using extended x-ray absorption fine structure (EXAFS) and x-ray diffraction. In this sample, these precipitates have a homogeneous composition, with about 10 wt.% Te. They retain a face-centered cubic structure as in pure Pd with a cell parameter which obeys Vegard's law. Pd K-edge EXAFS shows the presence of Te in the Pd coordination shell, with (Pd–Te) distances of 2.80 Å. These distances, higher by 0.05 Å than the (Pd–Pd) distances, may result in a lower packing efficiency of the CFC lattice. The comparison with the average distances derived from x-ray diffraction shows the nonmetallic character of the Pd–Te bond in these precipitates. These bonding modifications may cause the limited solubility of Te in metallic Pd.
A study of optical absorption and photoinduced effects in Ge–Se–Te amorphous system
Authors: Maged A. F. , Sanad A. M. , El-Fouly M. F. , Amin G. A. M.
Published: March 2008

Optical studies have been performed on amorphous films of the system Ge10Se90-xTex where (x = 20, 30, 40). The study revealed that as the Te content is increased, the optical band gap (Eg) was found to decrease. Photoinduced effects were studied on thin films samples irradiated with either white light or uv light. The shift in Eg due to photoirradiation disappears upon annealing the films at a temperature below the glass transition temperature. The effect of γ-radiation up to 8 kGy on the optical band gap was also investigated, and no detectable shift of the optical band gap was observed. The relationship between the optical band gap and both the average heat of atomization and the average coordination number of the compositions under investigation was studied.
Crystal structure of HgTlBa2CuOx studied by high-resolution electron microscopy
Authors: Oku Takeo , Nakajima Satoru
Published: March 2008

The structure model for HgTlBa2CuOx was proposed from high-resolution electron microscopy using residual indices. Averaged digital high-resolution image of the HgTlBa2CuOx showed the existence of separated Hg layers and oxygen vacancies in the double (Hg, Tl) layers. Image calculations based on the proposed structure model of HgTlBa2CuO5 agreed well with the observation, and showed low residual values. The present result indicates the stability of the (Hg, Tl) double layer structure would be due to the formation of oxygen vacancies in the Hg layers.
Model for zinc oxide varistor
Authors: Santos J. D. , Longo E. , Leite E. R. , Varela J. A.
Published: March 2008

Zinc oxide varistors are very complex systems, and the dominant mechanism of voltage barrier formation in these systems has not been well established. Yet the MNDO quantum mechanical theoretical calculation was used in this work to determine the most probable defect type at the surface of a ZnO cluster. The proposed model represents well the semiconducting nature as well as the defects at the ZnO bulk and surface. The model also shows that the main adsorption species that provide stability at the ZnO surface are O-, O2-, and O2.
Structural and electrochemical properties of Ti–Ru–Fe–O alloys prepared by high energy ball-milling
Authors: Yip S-H. , Guay D. , Jin S. , Ghali E. , Van Neste A. , Schulz R.
Published: March 2008

The structural and electrochemical properties of the Ti–Ru–Fe–O system have been studied over the whole ternary metal compositional range, keeping constant the oxygen content at 30 at.%. The phase diagram was explored systematically by varying the composition of the material along one of the following axes: (i) constant Ru content of 16 at. %; (ii) constant Ti/Ru ratio of 2; (iii) constant Ti/Fe ratio of 1.6. For O/Ti ratios equal or below unity, the most prominent peaks observed in the x-ray diffraction patterns belong to a B2 structure. For O/Ti ratio larger than unity, stable titanium oxide phases are formed, which coexist with a cubic Fe-like or hcp-Ru like phases depending on the Fe/Ru ratio. Powder compositions with stoichiometry close to Ti2RuFeO2 are of interest due to good electrocatalytic properties, long-term stability, and low Ru content.
Preparation of high solid content glass particle-polymethacrylate composite by an advance wetting method
Authors: Wu Yi Hong , Jada Siva , Xu Ren
Published: March 2008

An advanced wetting method is used to prepare a composite with a high content of ceramic particles in a matrix of photocured polymethylmethacrylate. The method allows for the preparation at minimum stirring of high quality samples with up to 59% solid in volume. The samples present reasonable flow characteristics prior to curing, with high hardness and fracture toughness in the fully cured state. Practical implications of the preparation method for dental restorative applications are studied. The method is also useful in the preparation of similar composites for other practical applications.
Pore geometry in woven fiber structures: 0°/90° plain-weave cloth layup preform
Authors: Lee S-B. , Stock S. R. , Butts M. D. , Starr T. L. , Breunig T. M. , Kinney J. H.
Published: March 2008

Composite preform fiber architectures range from the very simple to the complex, and the extremes are typified by parallel continuous fibers and complicated three-dimensional woven structures. Subsequent processing of these preforms to produce dense composites may depend critically on the geometry of the interfiber porosity. The goal of this study is to fully characterize the structure of a 0°/90° cloth layup preform using x-ray tomographic microscopy (XTM). This characterization includes the measurement of intercloth channel widths and their variability, the transverse distribution of through-cloth holes, and the distribution of preform porosity. The structure of the intercloth porosity depends critically on the magnitude and direction of the offset between adjacent cloth layers. The structures observed include two-dimensional networks of open pipes linking adjacent holes, arrays of parallel one-dimensional pipes linking holes, and relatively closed channels exhibiting little structure, and these different structures would appear to offer very different resistances to gas flow through the preform. These measurements, and future measurements for different fiber architectures, will yield improved understanding of the role of preform structure on processing.
Preparation and characterization of ultrafine TiO2 particles in reverse micelles by hydrolysis of titanium di-ethylhexyl sulfosuccinate
Authors: Lal Manjari , Chhabra Vishal , Ayyub Pushan , Maitra Amarnath
Published: March 2008

We describe the synthesis and characterization of ultrafine TiO2 particles (in both anatase as well as rutile form) produced by a chemical reaction within the aqueous core of a water-in-oil microemulsion. The microemulsion was stabilized and the Ti4+ ions provided by a functionalized surfactant derived from the commercially available Aerosol-OT, i.e., sodium bis (2-ethylhexyl) sulfosuccinate (Na-DEHSS). The Na+ ions in Aerosol-OT were completely replaced by Ti4+ through an ion-exchange reaction in nonaqueous solvents. Ultrafine TiO2 particles were produced by the hydrolysis of the Ti-containing surfactant in the water droplets. The dependence of the size of the precipitated TiO2 · xH2O particles on various structure parameters of the microemulsion was studied in detail.
Graded coatings by gradient temperature densification
Authors: Hur Sung Kang , Yoo Sang H. , Groza Joanna R. , Doh Jung Man , Yamazaki Kazuo , Shoda Kazuo
Published: March 2008

Functionally gradient materials (FGM) were prepared using layers of ZrO2 –3 mol% Y2O3 ceramic and NiCrAlY powders. A fine-grained zirconia powder was chosen to lower the ceramic sintering temperature and achieve simultaneous metal and ceramic densification. Consolidation of FGM's was achieved by a short time field-assisted sintering technique. Sintering was performed either at a constant temperature or in a temperature gradient by using punches made of different materials (i.e., one graphite and one tungsten). A temperature gradient of at least 100 °C was required with a low value of 1200 °C at the metal end and exceeding 1300 °C at the ceramic end. Increasing the number of intermediate layers alleviates some of the cracks formed during sintering due to different coefficients of thermal expansion.
Thickness dependence of microstructural evolution of ZnO films deposited by rf magnetron sputtering
Authors: Lee Yong Eui , Kim Young Jin , Kim Hyeong Joon
Published: March 2008

The microstructural evolution, including preferred orientation and surface morphology, of ZnO films deposited by rf magnetron sputtering was investigated with increasing film thickness. Preferred orientation of the ZnO films changed from (0002) → (1011) → (1120) and fine and dense columnar grains also changed to large elongated grains with increasing thickness. Such selective texture growth was explained with an effect of highly energetic species bombardment on the growing film surface. The relationship between preferred orientation change and microstructural evolution was also discussed.
Study on preparing PLT(28) thin film and its electro-optic effect
Authors: Ding Ai-Li , Luo Wei-Gen , Qiu P. S. , Feng J. W. , Zhang R. T.
Published: March 2008

PLT(28) thin films deposited on glass substrates were studied by two sputtering processes. One is an in situ magnetron sputtering and the other is a low-temperature magnetron sputtering. The sintered PLT ceramic powders are used as a sputtering target for both processes. The influences of sputtering and annealing conditions on structure and crystallinity of the films were investigated. The electro-optic (E-O) properties of PLT(28) thin films prepared by the two processes were determined by a technique according to Faraday effect. The researches showed the E-O properties were strongly affected by the sputtering process. The film with larger grains exhibits stronger E-O effect. The quadratic E-O coefficient of PLT(28) thin film varies in the range of 0.1 × 10−16 to 1.0 × 10−16 (m/v)2.
The oxidative transformation of solid, barium-metal-bearing precursors into monolithic celsian with a retention of shape, dimensions, and relative density
Authors: Allameh Seyed M. , Sandhage Kenneth H.
Published: March 2008

The conversion of Ba–Al2O3–Si–SiO2, Ba–Al–Al2O3–SiO2, and Ba–Sr–Al–Al2O3–SiO2precursors into monolithic, monoclinic celsian has been examined. The relative amounts of metal and oxide in each type of precursor were adjusted so that the overall stoichiometry and molar volume were similar to those of the desired product, celsian. Metal + oxide mixtures were mechanically alloyed and then uniaxially pressed to yield 84–92% dense precursor disks. The precursors were converted into celsian by exposure to a series of heat treatments from 300–1500 °C in oxygen-bearing gases. Differences and similarities in the phase evolution of the various precursors are discussed. Celsian disks were produced that retained the precursor shape, dimensions, and relative (% theoretical) density.
Simulations of fine ceramics cascade synthesized by the self-propagating high-temperature synthesis method
Authors: Chen Bai-Wai , Chen Chien-Chong
Published: March 2008

Due to the convective and radiant heat losses, there exists a maximal converted length of a dense pellet synthesized by the self-propagating high-temperature synthesis (SHS) method. In this paper, we numerically investigate the possibility to increase that maximal converted length by cascading two reactant pellets in series, where an interface is naturally and artificially introduced. First, the impacts of both the bulk and interfacial parameters on the SHS process are estimated. The maximal converted length for a single pellet is computed. Next, by varying the interfacial parameters, it is found that more than 10% of extra converted length is obtained by the proposed cascade arrangement. Effects of the bulk parameters on the same purpose are also addressed.
Determination of indenter tip geometry and indentation contact area for depth-sensing indentation experiments
Authors: McElhaney K. W. , Vlassak J. J. , Nix W. D.
Published: March 2008

The phenomena of pile-up and sink-in associated with nanoindentation have been found to have large effects on the measurements of the indentation modulus and hardness of copper. Pile-up (or sink-in) leads to contact areas that are greater than (or less than) the cross-sectional area of the indenter at a given depth. These effects lead to errors in the absolute measurement of mechanical properties by nanoindentation. To account for these effects, a new method of indenter tip shape calibration has been developed; it is based on measurements of contact compliance as well as direct SEM observations and measurements of the areas of large indentations. Application of this calibration technique to strain-hardened (pile-up) and annealed (sink-in) copper leads to a unique tip shape calibration for the diamond indenter itself, as well as to a material parameter, a, which characterizes the extent of pile-up or sink-in. Thus the shape of the indenter tip and nature of the material response are separated in this calibration method. Using this approach, it is possible to make accurate absolute measurements of hardness and indentation modulus by nanoindentation.
The Faraday effect in diamagnetic glasses
Authors: Qiu Jianrong , Hirao Kazuyuki
Published: March 2008

The wavelength dispersions of the Faraday effect in typical diamagnetic glasses, i.e., silica, borate, silicate, tellurite, lead-bismuth-gallate, and As2S3, have been examined. The Verdet constant of the glasses decreases with increasing wavelength in the longer wavelength region of the absorption edge of the glasses, while it increases with increasing optical bandgap of the glasses. These phenomena have been successfully explained based on the Becquerel theory. A guiding principle in designing a diamagnetic glass with a high Verdet constant is proposed.