bluuebunny/crossref_metadata_2025 huggingface dataset:
Valence states analysis of Ca and Si in CaSi2 during CaSi2–H2O reaction
Authors: Abe S. , Nakayama H. , Nishino T. , Iida S.
Published: March 2008

The changes in the valence electron states of CaSi2 during the chemical reaction with H2O have been investigated by Auger Valence Electron Spectroscopy (AVES). In order to study the reaction process, the reaction was precisely controlled by applying dc voltage between Pt electrode and CaSi2 specimen. The Si[2s, 2p,V] Auger spectra of CaSi2 specimen remain unchanged under the applied voltage lower than −15 V relative to the Pt electrode in H2O. At higher applied voltage, 3p components of Si[2s, 2p, V] (V = 3s, 3p) Auger spectra get weak while the 3s components increase drastically. The peak position due to Ca[2p, 3p, 3p] transitions gradually shifted toward the lower energy side by raising the applied voltage. The peak shift is due to the formation of Ca–O bonds in CaSi2. A new peak, which arises from the split of the valence electron states in Ca atoms due to the Ca–O bonds, appeared in Ca[2p, 3p,V] Auger spectra for CaSi2 after the reaction with H2O.
Oxidation of Sn Thin Films to SnO2. Micro-Raman Mapping and X-ray Diffraction Studies
Authors: Sangaletti Luigi , Depero Laura E. , Allieri Brigida , Pioselli Francesca , Comini Elisabetta , Sberveglieri Giorgio , Zocchi Marcello
Published: March 2008

The oxidation of tin layers deposited onto alumina substrates is investigated with the aim to identify the different steps of the process and obtain information on the sample homogeneity, phase segregation, and degree of oxidation. It is shown that at least three phases coexist at 450 °C, Sn, SnO, and SnO2, and remarkable inhomogeneities, already visible at an optical inspection, are found in the thin film. A micro-Raman mapping of the layer shows that these inhomogeneities are related to the presence of different Sn oxidation states, as evidenced by the inhomogeneous distribution of SnO and SnOx Raman bands. The thin film becomes homogeneous after annealing treatments above 550 °C, where only the SnO2 cassiterite phase is detected.
Synthesis, Structure, and Superconducting Properties of Tantalum Carbide Nanorods and Nanoparticles
Authors: Fukunaga Akihiko , Chu Shaoyan , McHenry Michael E.
Published: March 2008

Tantalum carbide nanorods and nanoparticles have been synthesized using a vapor-solid reaction path starting with CVD grown carbon nanotube precursors. Their structures were studied using XRD, TEM, and HRSEM. Superconducting properties were characterized using a SQUID magnetometer. For reactions at lower temperatures, carbide nanorods, which replicate the ∼14 nm diameter of the precursor carbon nanotubes, are observed. For higher temperature reactions, coarsened carbide nanoparticles (100–250 nm) are observed which have spherical or cubic-faceted morphologies. A morphological Rayleigh instability is postulated as initiating the transition from nanorod to nanoparticle morphologies. Stoichiometric bulk TaC crystallizes in the rock salt structure and has a superconducting transition temperature of 9.7 K. In TaC nanorods and nanoparticles, the superconducting properties correlate with the lattice parameter. Nanoparticles with a little higher lattice parameter than the ideal one show higher Tc and higher fields at which the superconductivity disappears than stoichiometric bulk TaC.
Effect of the Nanoparticles on the Structure and Crystallization of Amorphous Silicon Thin Films Produced by rf Glow Discharge
Authors: Bertran E. , Sharma S. N. , Viera G. , Costa J. , St'ahel P. , Cabarrocas P. Roca i
Published: March 2008

Thin films of nanostructured silicon (ns-Si:H) were deposited by plasma-enhanced chemical vapor deposition in the presence of silicon nanoparticles at 100 °C substrate temperature using a silane and hydrogen gas mixture under continuous wave (cw) plasma conditions. The nanostructure of the films has been demonstrated by diverse ways: transmission electron microscopy, Raman spectroscopy, and x-ray diffraction, which have shown the presence of ordered silicon clusters (1–2 nm) embedded in an amorphous silicon matrix. Because of the presence of these ordered domains, the films crystallize faster than standard hydrogenated amorphous silicon samples, as evidenced by electrical measurements during the thermal annealing.
Estimation of the Emissions of CO2, SOx, and NOx of Steel Alloys
Authors: Halada K. , Ijima K. , Yagi K.
Published: March 2008

The emissions of CO2, SOx, and NOx of various steel alloys in the production stage were calculated by using the unit requirement of each subsystem of the steel-making process, in order to compare the superiority from the viewpoint of the environmental issue among various types of steel alloys. As steel production is a typical integrated system with multiproducts, allocation of emissions to each product, effect of the composition, and sharing the load by the by-product gases are considered. Calculated values of emission were arranged for fifteen kinds of finished steel products and for arbitrary contents of alloying elements.
Crack Profiles in Applied Moment Double Cantilever Beam Tests
Authors: Hsueh C. H. , Sun E. Y. , Becher P. F. , Plucknett K. P.
Published: March 2008

In situ observations of crack propagation in an applied moment double cantilever beam specimen were used previously to obtain the R-curve behavior of ceramic composites. To predict the R-curve using constitutive models, knowledge of the crack profile is required to derive the bridging stress distribution along the crack length and to analyze the toughening effect. To predict the crack profile in an applied moment double cantilever beam test, both the deformation of the crack surface due to the bending moment and the movement of the crack surface due to the rigid body motion of the loading fixture need to be considered. The analytical solution for the crack profile is derived in the present study. The predicted crack profiles agree well with experimental measurements.
Formation of New Surface Layers on Ceramics by Ion Assisted Reaction
Authors: Koh S. K. , Son Y-B. , Gam J-S. , Han K-S. , Choi W. K. , Jung H-J.
Published: March 2008

Ar+ ions with 1 keV energy were irradiated on aluminum nitride in an O2 environment and on aluminum oxide in a N2 environment. AlON on AlN and AlN on Al2O3 are formed by the Ar1 irradiation in O2 gas and N2 gas environments, respectively, and the formation of new surface layers is confirmed on the basis of Al2p near core levels and O1s, N1s core levels XPS depth profile analysis. Cu(1000 Å) films were deposited by ion-beam sputtering on Ar+ irradiated/unirradiated AlN surfaces, and the change of the adhesion strength was investigated by a scratch test. Cu films deposited on the irradiated AlN under an O2 environment showed higher bond strength than that on the unirradiated AlN. The improvement of bond strength of Cu films on the AlN surface resulted from the interface bonds between Cu and the surface layers. The bending strength of polycrystalline Al2O3 irradiated by Ar+ ions in N2 environment was also increased and the formation of nitride layer on the alumina was confirmed. A possible new surface layer formation mechanism on ceramics by the ion assisted reaction has been discussed in terms of surface analysis, chemical bond, and mechanical strength.
Electronmicroscopical Study of the Formation of Iron Carbide Phases After High-fluence Carbon Ion Implantation into Iron at Low Temperatures
Authors: Hammerl C , Königer A. , Rauschenbach B.
Published: March 2008

Carbon ions were implanted with energies between 50 and 150 keV into thin iron layers at temperatures of –10 °C and –70 °C. Formation of iron carbide phases was studied as a function of fluence, which was varied from 1.2 × 1017 C+-ions/cm2 up to 1.4 × 1018 C+-ions/cm2. The sequence of phase transformation during subsequent annealing to temperatures of up to 450 °C was also investigated. Detailed analysis of structure and morphology was done by cross-sectional transmission electron microscopy and electron diffraction experiments. The existence of metastable iron carbide phases, θ-Fe3C, Χ-Fe5C2, η-Fe2C, and also the amorphous phase Fe(C), after high-fluence carbon ion implantation and the transformation of the formed metastable phases by subsequent annealing into the θ-Fe3C phase are demonstrated.
Crystallization Kinetics and Phase Transformation of Li2O–Fe2O3–MnO2–CaO–P2O5–SiO2 Glass
Authors: His Chi-Shiung , Wang Moo-Chin
Published: March 2008

The crystallization kinetics and phase transformation of 10Li2O–14Fe2O3–11MnO2–25CaO–5P2O5–35SiO2 (LFMCPS) glass have been investigated using differential thermal analysis (DTA), Χ-ray diffraction (XRD), and scanning electron microscopy (SEM). The major crystalline phase determined by XRD analysis was triphylite [Li(Fe0.5Mn0.5)PO4], β–wollastonite (β CaO SiO2) and magnetite (Fe3O4) as the minor phases. The nonisothermal kinetics of crystallization of the LMFCPS glass was investigated using DTA analysis. The activation energy of crystallization for LFMCPS glass was 74.6 kcalymol. The growth morphology parameter n was 0.98 at a heating rate of 5 °C/min and decreased to 0.74 as the heating rate increased to 20 °C/min. The numerical factor of crystallization mechanism m was 0.57 at low crystallization temperature and gradually decreased as the temperature increased. For the experiment, the parameters n and m were approximately one. These results indicated that the surface nucleation was dominant in LFMCPS glass crystallization.
Indentation plastic displacement field: Part I. The case of soft films on hard substrates
Authors: Tsui T. Y. , Vlassak Joost , Nix William D.
Published: March 2008

The plastic deformation behavior of Knoop indentations made in a soft, porous titanium/aluminum multilayered thin film on a hard silicon substrate is studied through use of the focused-ion-beam milling and imaging technique. Pileup is observed for indentations with depths larger than 30% of the total film thickness. Analysis of the indentation cross sections shows that plastic deformation around the indentation is partly accommodated by the closing of the pores within the multilayers. This densification process reduces the amount of pileup formed below that predicted by finite element simulations. Experimental results show that the pileup is formed by an increase of the titanium layer thickness near the edges of the indentation. The thickness increase is largest near the film/substrate interface and decreases toward the surface of the multilayered film. The amount of normal compression near the center of the indenter is characterized, and it is demonstrated that the deformation becomes more nonuniform with increasing indentation depth.
Initial stages of yield in nanoindentation
Authors: Kiely J. D. , Jarausch K. F. , Houston J. E. , Russell P. E.
Published: March 2008

We have used the interfacial force microscope to perform nanoindentations on Au single-crystal surfaces. We have observed two distinct regimes of plastic deformation, which are distinguished by the magnitude of discontinuities in load relaxation. At lower stresses, relaxation occurs in small deviations from elastic behavior, while at the higher stresses they take the form of large load drops, often resulting in complete relaxation of the applied load. These major events create a relatively wide plastic zone that subsequently deepens more rapidly than it widens. We discuss these findings in terms of contrasting models of dislocation processes in the two regimes.
Nanoindentation and incipient plasticity
Authors: Tadmor E. B. , Miller R. , Phillips R. , Ortiz M.
Published: March 2008

This paper presents a large-scale atomic resolution simulation of nanoindentation into a thin aluminum film using the recently introduced quasicontinuum method. The purpose of the simulation is to study the initial stages of plastic deformation under the action of an indenter. Two different crystallographic orientations of the film and two different indenter geometries (a rectangular prism and a cylinder) are studied. We obtain both macroscopic load versus indentation depth curves, as well as microscopic quantities, such as the Peierls stress and density of geometrically necessary dislocations beneath the indenter. In addition, we obtain detailed information regarding the atomistic mechanisms responsible for the macroscopic curves. A strong dependence on geometry and orientation is observed. Two different microscopic mechanisms are observed to accommodate the applied loading: (i) nucleation and subsequent propagation into the bulk of edge dislocation dipoles and (ii) deformation twinning.
A study of the submicron indent-induced plastic deformation
Authors: Robertson C. F. , Fivel M. C.
Published: March 2008

A new method has been developed to achieve a better understanding of submicron indent-induced plastic deformation. This method combines numerical modeling and various experimental data and techniques. Three-dimensional discrete dislocation dynamics simulation and the finite element method (FEM) were used to model the experimental conditions associated with nanoindentation testing in fcc crystals. Transmission electron microscopy (TEM) observations of the indent-induced plastic volume and analysis of the experimental loading curve help in defining a complete set of dislocation nucleation rules, including the shape of the nucleated loops and the corresponding macroscopic loading. A validation of the model is performed through direct comparisons between a simulation and experiments for a nanoindentation test on a [001] copper single crystal up to 50 nm deep.
Deconvolution of hardness from data obtained from nanoindentation of rough surfaces
Authors: Bobji M. S. , Biswas S. K.
Published: March 2008

Variation of hardness with penetration in nanoindentation of a rough surface is a compound effect of variation in asperity geometry with penetration, designated geometric effect, and genuine property gradients with depth as may exist in a near-surface zone. We simulate indentation of a rough surface numerically to elucidate the geometric effects and validate it by some model “macro” experiments. Finally, we formulate a general framework to deconvolute genuine property variation by normalizing the measured hardness with the geometric effect.
Subsolidus phase equilibria in the La2O3–Ga2O3–NiO system
Authors: Hrovat Marko , Bernik Slavko , Holc Janez , Samardžija Zoran
Published: March 2008

Subsolidus equilibria in air in the La2O3–Ga2O3–NiO system were studied with the aim of obtaining information on possible interactions between a LaGaO3-based solid electrolyte and NiO during preparation of the anode in solid oxide fuel cells (SOFC). No ternary compound was found. The tie lines are between La4Ga2O7 and La2NiO4, LaGaO3 and La2NiO4, LaGaO3 and NiO, and LaGaO3 and NiGa2O4.
Synthesis and characteristics of ZnS/CdS composite nanocrystals in block copolymer micelle
Authors: Wang Dayang , Cao Yaan , Zhang Xintong , Qian Xinming , Ai Xin , Liu Zhiqiang , Liu Fengqui , Wang Dejun , Bai Yubai , Li Tiejin , Tang Xinyi
Published: March 2008

In hydroxylated poly(styrene-b-butadiene-b-styrene) (HO–SBS) micelle, ZnS/CdS composite nanocrystals were prepared by adding Cd2+ ions and Zn2+ ions to the system sequentially. The resulting composites were identified with elemental analysis, transmission electron microscopy, x-ray diffraction, surface photovoltage spectroscopy, and electric field induced surface photovoltage spectroscopy.
Atomic force microscopic studies of oxide thin films on organic self-assembled monolayers
Authors: Niesen T. P. , Guire M. R. De , Bill J. , Aldinger F. , Rühle M. , Fischer A. , Jentoft F. C. , Schlögl R.
Published: March 2008

The surface morphology of TiO2- and ZrO2-based thin films, deposited from aqueous solution at 70–80 °C onto functionalized organic self-assembled monolayers (SAMs) on silicon has been examined using atomic force microscopy (AFM). The films have been previously shown to consist, respectively, of nanocrystalline TiO2 (anatase) and of nanocrystalline tetragonal ZrO2 with amorphous basic zirconium sulfate. The films exhibit characteristic surface roughnesses on two length scales. Roughness on the nanometer scale appears to be dictated by the size of the crystallites in the film. Roughness on the micron scale is postulated to be related to several factors, including the topography of the SAM and the effects of larger, physisorbed particles or agglomerates. The topographies of the oxide thin films, on both the nanometer and micron scales, are consistent with a particle-attachment mechanism of film growth.
Magnetoresistance, temporal evolution, and relaxation of the electrical resistivity in the re-entrant semiconducting La0.80Ba0.20CoO3 perovskite
Authors: Sánchez R. D. , Mira J. , Rivas J. , Breijo M. P. , Señarís-Rodríguez M. A.
Published: March 2008

We report here a study on the electrical and magnetic properties of La1−xBaxCoO3 in the re-entrant semiconducting region (x = 0.20). We find that in this material: (i) the insulator-metal-insulator sequence is unstable and evolves toward a purely semiconducting behavior; the initial r versus T curve can be reinstated upon appropriate annealing treatments; (ii) there are relaxation effects that can be seen by changing the polarity of the electrodes; (iii) there is a negative magnetoresistance Δρ/ρ ∼ 2–3%, for a field as low as 9 kOe, especially at the metal-insulating transition temperatures; and (iv) there are important fluctuations in the electrical resistivity. Taking into account these experimental observations, we can interpret this material as an inhomogeneous system where two thermodynamic phases, one semiconducting and the other metallic and ferromagnetic, coexist, although they are crystallographically indistinguishable.
Spark plasma sintering of Nd–Fe–B magnetic alloy
Authors: Liu Z. G. , Umemoto M. , Hirosawa S. , Kanekiyo H.
Published: March 2008

Spark plasma sintering was used to consolidate the crystallized Nd–Fe–B alloy powders. It was found that a higher sintering temperature can improve the consolidation significantly, whereas it deteriorates the magnetic properties drastically due to the appearance of a large amount of α–Fe phase and the grain growth. Sintering at lower temperature can preserve the magnetic properties better, while the powders cannot be consolidated into a fully dense compact, even under the higher pressure of 75 MPa. Finer starting powder particles show similar behavior.
An investigation of carbon nanotubes obtained from the decomposition of methane over reduced Mg1−xMxAl2O4 spinel catalysts
Authors: Govindaraj A. , Flahaut E. , Laurent Ch. , Peigney A. , Rousset A. , Rao C. N. R.
Published: March 2008

Carbon nanotubes produced by the treatment of Mg1−xMxAl2O4 (M = Fe, Co, or Ni; x = 0.1, 0.2, 0.3, or 0.4) spinels with an H2–CH4 mixture at 1070 °C have been investigated systematically. The grains of the oxide-metal composite particles are uniformly covered by a weblike network of carbon nanotube bundles, several tens of micrometers long, made up of single-wall nanotubes with a diameter close to 4 nm. Only the smallest metal particles (<5 nm) are involved in the formation of the nanotubes. A macroscopic characterization method involving surface area measurements and chemical analysis has been developed in order to compare the different nanotube specimens. An increase in the transition metal content of the catalyst yields more carbon nanotubes (up to a metal content of 10.0 wt% or x = 0.3), but causes a decrease in carbon quality. The best compromise is to use 6.7 wt% of metal (x = 0.2) in the catalyst. Co gives superior results with respect to both the quantity and quality of the nanotubes. In the case of Fe, the quality is notably hampered by the formation of Fe3C particles.
Orientation relationship and interfaces in nonfaceted-nonfaceted ZrO2(c)–CaZrO3 lamellar eutectics
Authors: Larrea A. , Orera V. M. , Peña J. I. , Merino R. I.
Published: March 2008

The orientation relationship and the interfaces of ZrO2(c)–CaZrO3 unidirectional solidified eutectics have been investigated by means of electron diffraction and transmission electron microscopy (TEM). In contrast to previous studies on lamellar oxide-oxide systems, neither a constant orientation relationship between contiguous lamellae nor low-index interfaces are observed in this eutectic. As for metals and plastic crystals, it displays incoherent interfaces and nonfaceted growth. This unusual behavior is discussed in terms of entropy of fusion and related to the presence of oxygen vacancies in the ZrO2(c) phase.
The decisive role of oxide content in the formation and crystallization of gallium-lanthanum-sulfide glasses
Authors: Li Ruihua , Furniss David , Bagshaw Heath , Seddon Angela B.
Published: March 2008

A series of gallium-lanthanum-sulfide (GLS) glasses of different oxide concentration has been made and their spectroscopic properties, thermal properties, and the crystallization behavior of the glasses have been studied. It was revealed that the formability of GLS glasses relies on the existence of a certain amount of oxide content. The thermal stability of GLS glasses changes as a function of oxide concentration. The results have also shown that increasing oxide content caused a shift of the visible absorption edge to shorter wavelengths and an increase of absorption intensity in the infrared region at the multiphonon edge. Two closely related crystalline phases have been identified in the crystallized GLS glasses. For the first time it has been revealed that thermally stable GLS glasses can be made near the eutectic point of these two crystal phases by introducing an optimized amount of oxide.
Hydrothermal growth of hydroxyapatite single crystals under natural convection
Authors: Teraoka K. , Ito A. , Onuma K. , Tateishi T. , Tsutsumi S.
Published: March 2008

Whiskerlike-shaped hydroxyapatite single crystals with the calcium-deficient nature were hydrothermally grown under natural convection by using a temperature-gradient-applied pressure vessel. With this method, crystals grew thinner with a smaller tapering angle than those grown under the nonconvection. Maximum length of the crystals grown under natural convection was 8.3 nm. The grown crystals survived without fracture through at least ten times maximum indentation (25 µm) of the three-point bending tests, showing the maximum bending angle of 62°. Average tensile strength of the crystals was 410.0 MPa.
In situ surface modification and growth of ultrasmooth amorphous carbon films by direct carbon ion-beam deposition
Authors: Sohn M. H. , Kim S. I.
Published: March 2008

Very thin (<,100 nm) amorphous carbon films were grown on silicon substrates by unfiltered and filtered direct carbon ion beams. In situ surface modification was performed using C- energies in the range of 300–500 eV prior to the growth of the film. By lowering the energy of the C− beam to 150 eV, an amorphous carbon film was continuously grown after the surface modification. High-resolution electron microscopy showed that the film/substrate interface was damaged by 400 and 500 eV C− beams. The carbon composition profile at the interface investigated by electron energy-loss spectroscopy illustrated that the 500 eV C− beam generated a 30 nm thick carbon/silicon mixing layer at the interface. The damage and mixing layers were not observed at 300 eV modification. Wear testing found that strong adhesion occurred in samples modified at 400 and 500 eV. However, at 300 eV, modified samples exhibited delamination failure, which indicated inferior adhesion of the films. Surface roughness evolution of 30, 60, and 90 nm thick films was investigated by atomic force microscopy. The film surface roughness decrease as a function of film thickness was much faster when the films were grown by the filtered C− beam.
Quasicrystalline phase formation in Al62Cu22.5Fe12.5 and Al55Cu22.5Fe12.5Be7 alloys
Authors: Lee S. M. , Kim B. H. , Kim D. H. , Kim W. T.
Published: March 2008

Formation of the icosahedral quasicrystalline phase in conventionally cast Al62Cu25.5Fe12.5 and Al55Cu25.5Fe12.5Be7 alloys were investigated. The icosahedral phase (I-phase) forming ability was greatly improved by partial replacement of Al by 7 at.% Be. The as-cast Al55Cu25.5Fe12.5Be7 alloy consisted of dendritic primary I-phase and interdendritic τ-phase, whereas that of an as-cast Al62Cu25.5Fe12.5 alloy consisted of various phases such as the β-, I-, and τ-phases, together with a small amount of the λ- and η-phases. The kinetic barrier for transformation into single I-phase by heat treatment was greatly reduced in an Al55Cu25.5Fe12.5Be7 alloy. The I-phase in an Al55Cu25.5Fe12.5Be7 alloy has the same face centered icosahedral structure as that in an Al62Cu25.5Fe12.5 alloy and is of high quality without phason strain.
A combinatorial approach for efficient mapping of phase diagrams and properties
Authors: Zhao Ji-Cheng
Published: March 2008

A methodology is developed which extends the combinatorial approaches to structural materials research and development. This high-efficiency methodology employs diffusion couples and “diffusion multiples” to create large variations (libraries) of compositions in bulk samples for fast and systematic surveys of bulk properties. These composition libraries coupled with microanalytical techniques such as electron probe microanalysis, electron backscatter diffraction analysis, and nanoindentation tests can be used for efficient surveys of phases, equilibria, diffusion coefficients, precipitation kinetics, properties, and composition–phase–property relations (such as solution hardening and strengthening effect) for accelerated design of multicomponent alloys.
Study of analysis methods of depth-sensing indentation test data for spherical indenters
Authors: Fischer-Cripps A. C.
Published: March 2008

The underlying theory behind the extraction of elastic modulus and hardness from the unloading load–displacement data obtained with a spherical indenter was explored in detail. A formal treatment of the effect of indenter elasticity was given, and the validity of the use of the reduced or combined modulus in analytical treatments was verified. The “Oliver and Pharr” method and the “Field and Swain” methods of analyses were compared in detail and shown to be equivalent.
Phase separation in SiO2–TiO2 gel and glassy films studied by atomic force microscopy and transmission electron microscopy
Authors: Karthikeyan A. , Almeida Rui M.
Published: March 2008

An investigation of phase separation phenomena in gel and glassy thin films of silica–titania, with TiO2 contents of 20 and 40 mol%, has been carried out by atomic force microscopy (AFM) and transmission electron microscopy (TEM). The thin films were prepared by spin coating of a precursor sol on silicon wafers. Both the TEM measurements (carried out on scrapped thin film flakes) and the AFM measurements (carried out on films coated on the silicon substrates) for samples with different heat treatments suggest that spinodal-like structural inhomogeneities occur in these samples, unlike the corresponding observations in pure silica films, which are known to be homogeneous. Changes in the microstructure of the films have been noticed with the thermal treatment, in agreement with earlier x-ray photoemission studies. The finer characteristic dimensions of the phase separated regions reveal that silica–titania samples prepared by sol-gel processing exhibit a more intimate mixing of the phases.
Electrical conductivity of vapor-grown carbon fiber/thermoplastic composites
Authors: Finegan Ioana C. , Tibbetts Gary G.
Published: March 2008

Conducting polymers are required for applications such as radio frequency interference shielding, primerless electrostatic painting, and static discharge. We have used vapor-grown carbon fiber (VGCF) as an additive to investigate conducting thermoplastics for these applications. The electrical properties of VGCF/polypropylene (PP) and VGCF/nylon composites are very attractive compared with those provided by other conventional conducting additives. Because of the low diameter of the VGCF used, the onset of conductivity (percolation threshold) can be below 3 vol%. Because of the highly conductive nature of the fibers, particularly after a graphitization step, the composites can reach resistivities as low as 0.15 Ω cm.
Formation and properties of Zr48Nb8Fe8Cu12Be24 bulk metallic glass
Authors: Zhang Yong , Zhao D. Q. , Wei B. C. , Wen P. , Pan M. X. , Wang W. H.
Published: March 2008

Zr/Nb-based bulk metallic glass (BMG) with a composition of Zr48Nb8Fe8Cu12Be24 was formed in cylindrical shapes 8 mm in diameter by the quartz tube water quenching method. The formation and acoustic, thermal, mechanical, and elastic properties of the BMG were investigated. The BMG exhibited excellent glass-forming ability, high thermal stability, and excellent mechanical properties.
Characteristics of elastic waves generated by crack initiation in aluminum alloys under fatigue loading
Authors: Nam Kiwoo , Mal Ajit
Published: March 2008

The characteristics of elastic waves emanating from crack initiation in 2024 and 5052 aluminum alloys subject to static and fatigue loading were investigated through laboratory experiments. The objective of the study was to determine the differences in the properties of the signals generated from static and fatigue tests and also to examine if the sources of the waves could be identified from the temporal and spectral characteristics of the acoustic emission waveforms. The signals were recorded using nonresonant, flat, broadband transducers attached to the surface of the alloy specimens. The time dependence and power spectra of the signals recorded during the tests were examined and classified according to their special features. Three distinct types of signals were observed. The waveforms and their power spectra were found to be dependent on the material and the type of fracture associated with the signals. Analysis of the waveforms indicated that some signals could be attributed to plastic deformation associated with static tests. The potential application of the approach in health monitoring of aging aircraft structures using a network of surface mounted broadband sensors is discussed.
Devitrification kinetics and mechanism of Pyrex borosilicate glass
Authors: Jean Jau-Ho , Fang Yu-Ching
Published: March 2008

Cristobalite is formed when initially amorphous Pyrex borosilicate glass (Corning 7740) is fired at temperatures ranging from 700 to 1000 °C. The sigmoidal devitrification kinetics of cristobalite obeys Avrami-like three-dimensional diffusion-controlled kinetics. Activation energy analysis indicates that the diffusion of Na+ in the glass is the rate-limiting step during phase transformation. The above conclusion is further confirmed by calculated and measured results of linear growth rates.
Growth study of epitaxial FexZn1−xF2 thin films
Authors: McChesney J. , Hetzer M. , Shi H. , Charlton T. , Lederman D.
Published: March 2008

The FexZn1−xF2 alloy has been shown to be a model system for studying the magnetic phase diagram of dilute magnets. Whereas the growth of bulk single crystals with fixed Zn concentrations is difficult, the thin film growth is comparatively simpler and more flexible. To gain an understanding of the growth of FexZn1−xF2 films, a method was developed to grow smooth films at fixed concentrations. This was done by depositing a MgF2 buffer layer on MgF2(001) substrates and then depositing FeF2 and ZnF2 [001]-orientated epitaxial thin films at different temperatures. Surprisingly, the lattice spacing depends strongly on the growth temperature, for 44-nm-thick FeF2 films and 77-nm-thick ZnF2 films. This indicates a significant amount of stress, despite the close lattice match between the films and the MgF2 substrate. Thick alloy samples (approximately 500 nm thick) were grown by co-evaporation from the FeF2 and ZnF2 sources at the ideal temperature determined from the growth study, and their concentration was accurately determined using x-ray diffraction.
Determination of the elastic properties of glasses and polymers exploiting the resonant characteristic of depth-sensing indentation tests
Authors: Lorenz D. , Fränzel W. , Einax M. , Grau P. , Berg G.
Published: March 2008

Depth-sensing indentation tests can be used to estimate the Young's modulus, hardness, and other characteristics of material behavior. For many materials, the unloading segment of the load–depth curve contains only elastic recovery while the loading segment can contain elastic and plastic deformation. In this paper a new method is presented to determine the Young's modulus of a material from the loading segment of an indentation test. A depth-sensitive hardness tester was used with a load cell integrated into the closed-loop system. Defined mechanical oscillations with constant frequency were generated by adding a piezoelectric stack to the closed loop of the hardness measurement system. Thus the resonance response of the system was obtained, which includes information regarding the stiffness of the tested material. This new method was tested on two polymers and two glasses, an optical and a conventional one. The results obtained for the Young's modulus were in good agreement with other accepted methods.
Influence of sintering atmosphere on the fabrication of SiC ceramics with a powder mixture of sialon composition
Authors: Lee Jong-Kook , Park Jong-Gon , Lee Eun-Gu , Kim Kyung-Seok
Published: March 2008

Silicon carbide ceramics with a powder mixture of sialon composition as a densification aid were prepared by hot pressing through a transient liquid phase, and the effects of sintering atmosphere and starting phases on the microstructural characteristics were investigated. The sintered SiC with the additive of a Y–α-sialon composition in argon showed high sintered density and grains with large aspect ratio. But sintered specimens in nitrogen yielded grains with low aspect ratio and small grain size, because of the retardation of phase transformation and grain growth. The SiC specimen prepared from the starting β–SiC powder with Y–α-sialon composition showed the highest fracture toughness of approximately 6.0 MPa m1/2.
X-ray scattering study on the structural evolution of AlN/sapphire(0001) films during radiofrequency sputter growth
Authors: Kang H. C. , Seo S. H. , Noh D. Y.
Published: March 2008

We present an x-ray scattering study on the evolution of the growth mode, the surface morphology, and the lattice strain of AlN/sapphire(0001) films during sputter growth. Aligned epitaxial planar layers with strain relaxed to about 2% are nucleated during initial stage growth. As the film thickness increases to an effective “critical” thickness of approximately 250 Å, the growth gradually crosses over to the less aligned island growth. As the growth crossover occurs, the growth front becomes substantially rougher and the residual strain begins to relax. The cogrowth of the planar layer and the islands results in a nonuniform strain distribution.
Superplasticicity of Cu–16 at.% Ag microcomposites
Authors: Hong S. I. , Kwon H. J.
Published: March 2008

Superplastic behavior of heavily drawn Cu–at.% Ag filamentary microcomposite wires was investigated. The filamentary microstructure tended to break up at high temperatures by spheroidization, grooving, and/or recrystallization because of its high interface energy and high cold-work energy. Above 400 °C, extensive recrystallization occurred and the grains 300–500 nm in size were observed in the Cu matrix. As the deformation proceeded, the elongated silver lamellae and/or the region with numerous filaments broke up and rearranged into chevron patterns, which mostly lay perpendicular to the loading axis. The elongation up to 1000% was obtained at 500 °C at the strain rates of 7 × 10−4/s and −3 × 10−3/s, and the elongation up to 600% was obtained at 400 °C at the strain rate of 1 × 10−4/s. Arrays of dislocations in the matrix and near grain and phase boundaries were observed after superplastic deformation, supporting the slip-accommodated grain and/or phase boundary sliding.
Metalorganic chemical vapor deposition of titanium oxide for microelectronics applications
Authors: Vydianathan Kanchana , Nuesca Guillermo , Peterson Gregory , Eisenbraun Eric T. , Kaloyeros Alain E. , Sullivan John J. , Han Bin
Published: March 2008

A chemical vapor deposition process has been developed for titanium dioxide (TiOx) for applications as capacitor dielectric in sub-quarter-micron dynamic random-access memory devices, and as gate insulators in emerging generations of etal-oxide-semiconductor transistors. Studies using the β-diketonate source precursor (2,2,6,6-tetramethyl-3,5-heptanedionato) titanium were carried out to examine the underlying mechanisms that control film nucleation and growth kinetics and to establish the effects of key process parameters on film purity, composition, texture, morphology, and electrical properties. Resulting film properties were thoroughly analyzed by x-ray diffraction, x-ray photoelectron spectroscopy, Rutherford backscattering spectrometry, scanning electron microscopy (SEM), focused-ion-beam SEM, and capacitance–voltage (C–V) measurements. The study resulted in the identification of an optimized process for the deposition of an anatase–rutile TiOx film with a dielectric constant approximately 85 at 1 MHz for a 330-nm thickness, and a leakage current below 2 × 10−8 A/cm2 for bias voltage values up to 3.5 V.
Submicron-grained multiphase TiAlSi alloys: Processing, characterization, and microstructural design
Authors: Bohn R. , Fanta G. , Klassen T. , Bormann R.
Published: March 2008

Prealloyed powders of the intermetallic γ–TiAl phase and the ceramic Ξ–Ti5Si3phase were high-energy milled and hot-isostatically pressed (HIP) to produce silicide dispersed composite materials with grain sizes in the submicron and nanometer range. The amorphous state of the as-milled powders crystallizes via a multistep decomposition reaction during degassing at 440 °C and HIP. At a pressure of 200 Mpa HIP-temperatures as low as 750 °C are sufficient for a complete densification of the milled powder. The microstructure of the compacts is very homogeneous and consists of equiaxed γ–TiAl crystals and Ξ–Ti5(Si,Al)3particles. Depending on the silicon content, these particles are interspersed within the grain boundary network of the γ–TiAl phase or dispersed inside the γ grains. With respect to technical applications, submicron-grained composites are regarded as promising precursor materials that should allow for easy hot working in the as-prepared state as well as for high-temperature structural applications after a suitable transformation of the microstructure.
Síndrome de Kallmann: uma revisão histórica, clínica e molecular
Authors: Ribeiro Rogério Silicani , Abucham Julio
Published: March 2008

A síndrome de Kallmann (SK) é a associação de hipogonadismo hipogonadotrófico (HH) e anosmia descrita por Maestre de San Juan, em 1856, e caracterizada como condição hereditária por Franz Josef Kallmann, em 1944. Muitos aspectos de sua patogenia, variabilidade fenotípica e genotípica foram desvendados nos últimos 15 anos. Conseqüentemente, tem sido difícil manter-se atualizado frente à rapidez que o conhecimento dessa condição é gerado. Nesta revisão, resgatamos aspectos históricos pouco conhecidos sobre a síndrome e seus descobridores; incorporamos novas descobertas relacionadas à embriogênese dos neurônios olfatórios e produtores de GnRH. Esse processo é fundamental para compreender a associação de hipogonadismo e anosmia; descrevemos a heterogeneidade fenotípica e genotípica, incluindo mutações em cinco genes (KAL-1, FGFR1, PROKR2, PROK2 e NELF). Para cada gene, discutimos a função da proteína codificada na migração e maturação dos neurônios olfatórios e GnRH a partir de estudos in vitro e modelos experimentais e descrevemos características clínicas dos portadores dessas mutações.
Blood pressure and cardiorenal responses to antihypertensive therapy in obese women
Authors: Rosa Eduardo Cantoni , Zanella Maria Tereza , Kohlmann Nárcia Elisa Bellucci , Ferreira Sandra Roberta Gouveia , Plavnik Frida Liane , Ribeiro Artur Beltrame , Kohlmann Jr. Osvaldo
Published: March 2008

OBJECTIVE: Blood pressure(BP) and target organ responses to antihypertensive drugs are not well established in hypertensive obese patients. This study is aimed at evaluating the effects of obesity and adiposity distribution patterns on these responses. METHODS: 49 hypertensive obese women were designated to different groups according to waist to hip ratio measurements - 37 with troncular and 12 with peripheral obesity. Patients were treated for 24-weeks on a stepwise regimen with cilazapril alone or a cilazapril/hydrochlorothiazide/amlodipine combination therapy to achieve a BP lower than 140/90mmHg. Ambulatory blood pressure monitoring (ABPM), echocardiography, and albuminuria were assessed before and after the intervention. RESULTS: After 24 weeks, weight loss was less than 2% in both groups. ABPM targets were achieved in 81.5% of patients upon a combination of 2(26.5%) or 3(55.1%) drugs. Similar reductions in daytime-SBP/DBP: -22.5/-14.1(troncular obesity) / -23.6/-14.9mmHg (peripheral obesity) were obtained. Decrease in nocturnal-SBP was greater in troncular obesity patients. Upon BP control, microalbuminuria was markedly decreased, while only slight decrease in left ventricular mass was observed for both groups. CONCLUSIONS: In the absence of weight loss, most patients required combined antihypertensive therapy to control their BP, regardless of their body fat distribution pattern. Optimal target BP and normal albuminuria were achieved in the group as a whole and in both obese patient groups, while benefits to cardiac structure were of a smaller magnitude.
Análise da taxa metabólica de repouso avaliada por calorimetria indireta em mulheres obesas com baixa e alta ingestão calórica
Authors: Rodrigues Alessandra E. , Marostegan Patrícia Freire , Mancini Marcio C. , Dalcanale Lorença , Melo Maria Edna de , Cercato Cíntia , Halpern Alfredo
Published: March 2008

Este trabalho analisou se mulheres obesas com baixa ingestão calórica (IC), aferidas por questionário alimentar, apresentam valores diminuídos de taxa metabólica de repouso (TMR), o que favoreceria um desequilíbrio no balanço energético (BE) e conseqüente ganho de peso. Foram avaliados o índice de atividade física (AF) e sua relação com a IC em 77 mulheres obesas, com índice de massa corporal (IMC) acima de 30 kg/m², entre 20 e 45 anos. A partir dos valores da IC, as mulheres foram divididas em três grupos: baixa (G1), média (G2) e alta (G3) IC e submetidas a exame de calorimetria indireta de repouso. Foram avaliados: peso, altura, superfície de área corpórea (SAC), composição corporal por bioimpedância. O G1 apresentou maior valor de peso, SAC, peso de gordura corpórea e também valores abaixo de 1,2 na razão IC:TMR, o que indica provável subestimação da IC. Os maiores valores de AF e de TMR (por quilo de massa magra) foram verificados no G3. O G1 apresentou o BE mais negativo. O G3 apresentou valores positivos. Em suma, este estudo mostrou que existe tendência à subestimação da IC de algumas mulheres obesas e que a manutenção do peso corporal em algumas pacientes se deve ao baixo nível de AF.
Premature thelarche: clinical and laboratorial assessment by immunochemiluminescent assay
Authors: Borges Maria F. , Pacheco Kátia D. , Oliveira Andréia A. , Rita Cláudia V. C. , Pacheco Karla D. , Resende Elisabete A. M. , Lara Beatriz H. J. , Ferreira Beatriz P.
Published: March 2008

In order to establish cut-off limits and to distinguish isolated premature thelarche (IPT) from precocious puberty (PP), we evaluated data from 79 girls with premature thelarche, comparing basal and stimulated LH and FSH serum concentrations with those from 91 healthy girls. A GnRH stimulation test was performed in 10 normal girls and in 42 with premature thelarche. Comparison among groups was performed by Kruskal-Wallis and Dunn’s tests. LH values were significantly greater in girls with IPT than in control groups. Basal gonadotropin concentrations were higher in patients with PP than in controls, but not different from patients with IPT. Peak LH levels after GnRH stimulation distinguished those two groups, with a cut-off value of 4.0 IU/L, but still with minimal overlap. In conclusion, a girl with premature thelarche and LH peak value above 4.5 IU/L has, indeed, PP, but values between 3.5 and 4.5 IU/L point to careful follow-up.
Metformina e AMPK: um antigo fármaco e uma nova enzima no contexto da síndrome metabólica
Authors: Santomauro Jún Augusto Cézar , Ugolini Michelle Remião , Santomauro Ana Teresa , Souto Ricardo Peres do
Published: March 2008

A metformina é uma das drogas antidiabéticas orais mais prescritas mundialmente, entretanto seu mecanismo de ação permanece desconhecido. Os estudos do Diabetes Prevention Program Research Group demonstraram que tanto a administração de metformina como a mudança no estilo de vida (dieta e exercício físico) podem reduzir a incidência de diabetes melito tipo 2 (DM2). Uma possível conexão bioquímica entre essas duas terapias pode ser a proteína quinase ativada por AMP (AMPK). Essa enzima foi inicialmente descrita como um sensor energético celular, sendo ativada pelo exercício físico. Por outro lado, várias evidências experimentais indicam que a AMPK seja um alvo importante da ação da metformina. Este artigo discute as várias formas da regulação da AMPK, sugerindo um possível mecanismo para sua ativação pela metformina que envolve a formação de espécies reativas de nitrogênio. A ativação da AMPK determina ampla variedade de efeitos fisiológicos, incluindo o aumento da captação de glicose pelos músculos esqueléticos e aumento do catabolismo de lipídios, podendo ser interessante não apenas na prevenção e tratamento do DM2, mas também no contexto da síndrome metabólica. A descoberta da ativação da AMPK pela metformina faz dessa enzima importante alvo farmacológico.
Screening tests are not enough to detect hemineglect
Authors: Lopes Manuel Alvim Leite , Ferreira Hebert Pereira , Carvalho Juliana Costa , Cardoso Lídia , André Charles
Published: March 2008

OBJECTIVE: To verify the sensitivity of the conventional subtests of the Behavioral Inattention Test (BIT) in the diagnosis of hemineglect after stroke. METHOD: One hundred and two patients with cerebral infarct or hemorrhage were prospectively evaluated. In 22, hemineglect was diagnosed using standard BIT criteria. The frequency of hemineglect using 6 commonly used screening subtests of this battery was assessed. RESULTS: Hemineglect would not be recognized in 10 patients if they were only screened using the line crossing test; this would be the case in 2 patients with the letter cancellation test; and in 4 patient with the line bisection test. Three patients would not be diagnosed even if both line crossing and line bisection tests were used. CONCLUSION: Hemineglect may not be recognized with single screening tests commonly used. The use of a standard battery is recommended to improve diagnostic sensitivity in individuals with various subtypes of hemineglect.