Thermodynamic Regularities in Perovskite and K2NiF4 Compounds

It has been found that the enthalpy of formation of perovskite compounds, Δ_fH° (ABO₃, B = transition metais), from binary oxides can be well characterized in terms the tolerance factor, t≡(r_A+ r_o)√2 (r_B+ r_o), where r_A and r_B are the radii of A-site ions with 12-coordination and B-site ions with 6-coordination, respectively, and Δ_fH°=−168 + 270(1 − t) kJ·mol⁻¹ for A^IB^VO₃, Δ_fH°=−125 + 1000(1 − t) kJ·mol⁻¹ for A^IIB^IVO₃, and Δ_fH°=− 90 + 720(1 − t) kJ·mol⁻¹ for A^IIIB^IIIO₃. Although the thermodynamic data of K₂NiF₄ compounds are not extensive, a similar regularity can be found when use is made of the radii of A-site ions with 9-coordination for the K₂NiF₄ compounds. These correlations will be quite useful in predicting.     

A Modified Nonparametric Prewhitened Covariance Estimator

Abstract. This paper proposes a fully modified version of the spectral matrix estimator (and the long‐run variance estimator as a special case) proposed originally by Xiao and Linton [Journal of Time Series Analysis (2002) Vol. 23, pp. 215–250], and derives its asymptotic results. A striking feature of the modified spectral matrix estimator is to achieve the convergence rate of O(T ^?8/9) in the mean squared error (MSE), which is usually achieved under the fourth‐order spectral window. However, this estimator does not sacrifice the positive definiteness of the resulting estimate for the rate improvement; it is Hermitian and positive definite in finite samples by construction. The faster convergence rate is established by a multiplicative bias correction of the crude spectral estimator under the second‐order spectral window. The approximations to some sensible definitions of the MSE of the estimator and the bandwidths that minimize the asymptotic MSEs are also derived. Monte Carlo results indicate that for a wide variety of processes the modified spectral matrix estimator reduces the bias without inflating the variance and thus improves the MSE, compared with the crude, bias‐uncorrected estimator.     

Development of an anisotropic conductive adhesive film (ACAF) from epoxy resins

A thermoset type anisotropic conductive adhesive film (ACAF), which electrically connects an ITO glass and a flex circuit both having conducting pattersn of less than 100 μm in pitch, has been developed. In this development, bisphenol A and bisphenol F epoxy resins were tested to formulate an ACAF with easy-to-handle tackiness, flexibility, and strenght. A curing agent that gives fast cure and long shelf-life properties to the epoxy resin was also selected. The tensile stress–strain responses of obtained adhesive films were successfully used for determining the formulation. Good aftercure physical properties (electrical and mechanical) were obtained. Durability against high temperature and high humidity were also tested to confirm long-term stability of the conduction of this ACAF. © 1995 John Wiley & Sons, Inc.     

Dielectric Depression and Dispersion in Electrophoretically Fabricated BaTiO3 Ceramic Films

Dielectric depression and dispersion were observed in BaTiO3 ceramic films fabricated by electrophoretic deposition followed by sintering. The dielectric constants were depressed down to 6800–4600 around the Curie point ( T _C ). The dielectric dispersion occurred above T _C . These dielectric properties are attributable to a surface layer formed during sintering. XRD analysis indicated that the surface layer was a hexagonal-like BaTiO₃ phase. A mixed solvent of acetylacetone and alcohol employed in the present work may have been responsible for the formation of the surface layer.     

Characterization of Silicon Carbide–Silicon Nitride Composite Ultrafine Particles Synthesized Using a CO2 Laser by Silicon-29 Magic Angle Spinning NMR and ESR

The structure of silicon carbide–silicon nitride (SiC–Si₃N₄) composite particles synthesized using a CO₂ laser was studied by magic angle spinning nuclear magnetic resonance (MAS-NMR) and electron spin resonance (ESR). The structure around Si atoms changed by introducing N. C atoms around Si were substituted by N atoms, and N-rich configurations around Si atoms increased stepwise as the N content increased. The low N content composite particles consisted of mainly SiC phase containing dissolved N. N atoms were partly present in β-SiC microcrystal and partly in the grain boundary layer in the particle. N atoms were tetrahedrally surrounded by four Si atoms in β-SiC microcrystal and were trivalent state bonded to three Si atoms in the grain boundary layer. The high N content particles consisted of SiC, Si₃N₄, and amorphous phases, whose amount depended on N content.     

Formation of Small-Sized CdSxSe1-x Crystals in Sol-Gel-Derived SiO2 Glasses

Silica glasses doped with small-sized CdS_x-Se_1-x crystals were prepared by the sol-gel method. Gels synthesized by the hydrolysis of Si(OC₂H₅)₄, in the presence of CdSeO₄ with NH₄SCN dissolved in HNO₃ or NH₄OH, were heated in H₂-N₂ atmosphere. The pH value of solutions for CdSeO⁴ and NH⁴SCN primarily determined the fraction of anions in CdS^xSe^1-x crystals. The anion content in crystals was dependent on the pH value of the solvent and/or heat-treatment temperature, and the sulfur fraction changed from 0.1 to 0.6. The optical absorption spectra were red-shifted as the selenium content and the crystal size increased, and the emission spectra showed a sharp band near the absorption edge position and a broad tail extending into the long wavelength. The optical band gap energies increased reciprocally proportional to the square of the crystal size.     

Ring hydrogenation of naphthalene and 1-naphthol over supported metal catalysts in supercritical carbon dioxide solvent

Catalytic ring hydrogenations of naphthalene and 1-naphthol were studied over several supported metal catalysts in supercritical carbon dioxide solvent at low temperature. Higher concentration of hydrogen in supercritical carbon dioxide and lower reaction temperature were responsible for higher catalyst activity and selectivities to the desired partial ring hydrogenated products as compared with those observed in organic solvent for the same catalyst.     

Dehydration of Gels and Glasses in the Systems B2 O3-SiO2 and ZrO2-SiO2 Prepared by the Sol-Gel Process from Metal Alkoxides

Dehydration of gels prepared by the sol-gel process from metal alkoxides in the systems B₂O₃-SiO₂ and ZrO₂-SiO₂ was determined by measuring the shrinkage of the gel on heating. Dehydration was enhanced with increased ZrO₂ content, whereas it decreased with B₂O₃ content. Diffusion of water was also measured in the nonporous glasses obtained by heating the gels. The diffusion rate was independent of the composition of the glass.     

Thermal strain of high strength polyethylene fiber in low temperature

High strength polyethylene fiber (Toyobo, Dyneema® fiber: hereinafter abbreviated to DF) has a negative thermal expansion coefficient. Relation between fiber structure and thermal strain of DF used as reinforcement of DF reinforced plastic (DFRP) for cryogenic use was investigated. The crystallinities and orientation angles of several kinds of polyethylene fibers having different modulus from 15 to 134Gpa (herein after abbreviated to DFs) were measured by NMR and X‐ray. We obtained the parameters of the mechanical series‐parallel model composed of crystal and amorphous by crystallinity and modulus. Thermal expansion coefficients of DFs were estimated by mechanical series‐parallel model. All DFs having different modulus showed negative thermal expansion coefficients in the temperature range from 180 to 300K, and absolute values of those markedly increased by increasing tensile modulus of DF. The estimated thermal expansion coefficients showed negative values, and thermal strains showed a similar curve to observed ones mostly. Average thermal expansion coefficients in the temperature range from 180 to 300K estimated by mechanical model agreed with the observed ones. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2918–2925, 2004     

Alternative technologies for biotechnological fuel ethanol manufacturing

The challenges of implementing biorefineries on a global scale include socioeconomic, financial, and technological constraints. In particular, the development of biorefineries is tightly linked to the continued availability of fermentation raw materials. These constraints can be relaxed by the use of diverse raw materials, while advances that confer higher flexibility would enable biotechnological plant managers to swiftly react to volatile markets. In conventional processes, Saccharomyces cerevisiae grows on a relatively limited range of substrates, and produces only a single product—ethanol. Given the observed maturity of the S. cerevisiae fermentation technology, alternatives to baker's yeast may be needed to tip the economic balance in favour of biotechnological ethanol. These alternative fermentation technologies may allow a greater diversity of substrates to be used to produce an individually tailored mix of ethanol and other chemicals. Copyright © 2007 Society of Chemical Industry