Electronic structure of the ladder-chain compound Sr14−xCaxCu24O41

The electronic structure of the ladder-chain compound Sr_14−xCa_xCu₂₄O₄₁ is studied by ab initio calculations within the local density approximation. The effects of Ca substitution and structure modulation on electronic structure are discussed. It is found that 0.05 holes per copper atom are on the ladder layers for fully substituted compound, Ca₁₄Cu₂₄O₄₁.     

Formation,Structure, and Crystallization Behavior of Cu-Based Bulk Glass-Forming Alloys

We studied Cu-Zr–based alloys having exceptionally high glass-forming ability (GFA) and investigated the influence of Ag and Al addition on their structure and crystallization behavior. Most of the bulk glassy alloys (BGAs) do not contain any crystals, while some samples studied by high-resolution transmission electron microscopy (HRTEM) were found to contain well-developed medium-range order zones and nanoparticles in a bulk form. The crystallization kinetics of Cu₅₅Zr₄₅, Cu₅₀Zr₅₀, Cu_55–x Zr₄₅Ag _x (x = 0, 10, 20), Cu₄₅Zr₄₅Al₅Ag₅, Cu₄₄Ag₁₅Zr₃₆Ti₅, and Cu₃₆Zr₄₈Al₈Ag₈ glassy alloys was analyzed. An influence of the cooling rate on the formation of glassy phase and thermal stability of the Cu-based glassy alloys on heating was also studied. The crystallization kinetics and phase composition of the ribbon-shape and bulk glassy samples of Cu₃₆Zr₄₈Al₈Ag₈ alloys were also analyzed. The results also indicate that the best glass-forming compositions are possibly located at slightly off-eutectic area, owing to the shift of the eutectic point due to the nonequilibrium processing conditions.     

Yield stress of duplex stainless steel specimens estimated using a compound Hall–Petch equation

In this study, the 0.2% yield stress of duplex stainless steel was evaluated using a compound Hall–Petch equation. The compound Hall–Petch equation was derived from four types of duplex stainless steel, which contained 0.2–64.4 wt% δ-ferrite phase, had different chemical compositions and were annealed at different temperatures. Intragranular yield stress was measured with an ultra-microhardness tester and evaluated with the yield stress model proposed by Dao et al. Grain size, volume fraction and texture were monitored by electron backscattering diffraction measurement. The k_γ constant in the compound equation for duplex stainless steel agrees well with that for γ-phase SUS316L steel in the temperature range of 1323–1473 K. The derived compound Hall–Petch equation predicts that the yield stress will be in good agreement with the experimental results for the Cr, Mn, Si, Ni and N solid-solution states. We find that the intragranular yield stress of the δ-phase of duplex stainless steel is rather sensitive to the chemical composition and annealing conditions, which is attributed to the size misfit parameter.     

Structure extraction from decorated characters using multiscaleimages

Decorated characters are widely used in various documents. Practical optical character reader is required to deal with not only common fonts but also complex designed fonts. However, since the appearances of decorated characters are complicated, most general character recognition systems cannot give good performances on decorated characters. In this paper, an algorithm that can extract character's essential structure from a decorated character is proposed. This algorithm is applied in preprocessing of character recognition. The proposed algorithm consists of three procedures: global structure extraction, interpolation of structure and smoothing. By using multiscale images, topographical features, such as ridges and ravines are detected for structure extraction. Ridges are used for extracting global structure and ravines are used for interpolation. Experimental results show character structures can be clearly extracted from very complex decorated characters     

Contribution of shape on ignition of polymeric materials

The contribution of the shape and size of polymers towards ignition for four kinds of polymers, PP (polypropylene), HIPS (rubber reinforced polystyrene), ABS (acrilonitril‐butadiene‐styrene copolymer) and PC (bisphenor‐A type polycarbonate) was studied. The critical heat flux (CHF), which means that the specimen ignites after infinite time, depended on the shape and kind of polymer at the plane position heating. But it was not affected by these conditions at the side position heating. The CHF and other phenomena of ignition were analyzed and the two regions in one of which the shape and the kind of polymer affects them and in another region they was not affected. It will be useful to design electrical parts that reduce fire risks. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Thermoelectric properties of porous zinc oxide ceramics doped with praseodymium

We evaluated praseodymium (Pr) doping effects on thermoelectric properties of porous zinc oxide (ZnO) ceramics. The low density ceramics composed of ZnO and an additive of Pr (0.5 and 0.1 mol%) oxide were prepared by sintering processes in different atmospheres (air and oxygen), where the additives were Pr₆O₁₁ known for phase transformations and the trioxide Pr₂O₃ with low valence state different from Pr₆O₁₁. Thermoelectric properties of the samples were measured between 313 K and 903 K. At high-temperature around 590 K, some samples showed a maximum of electrical resistivity. We discussed the origin of the maximum on the basis of carrier transport model on gas sensor and varistor. From the results, The maximum appearance was attributable to an interchange of carriers through defects complex closely related with enhanced zinc vacancies acceptor-like in the vicinity of grain boundaries (GB), where the defect complex seemed to be caused by Pr with valence state between 3+ and 3.78+ around GB. The doping Pr into ZnO matrix is expected to be advantageous to improve thermoelectric power.     

Effect of gravity on pool boiling heat transfer on thermal spray coating

This study deals with heat transfer enhancement surface manufactured by thermal spraying. Two thermal spraying methods using copper as a coating material, wire flame spraying (WFS) and vacuum plasma spraying (VPS), were applied to the outside of copper cylinder with 20 mm OD. The surface structure by WFS was denser than that by VPS. The effect of gravity on boiling heat transfer coeffcient and wall superheat at the onset of boiling were experimentally evaluated under micro- and hyper-gravity condition during a parabolic trajectory flight of an airplane. Pool boiling experiments in saturated liquid of HCFC123 were carried out for heat fluxes between 1.0 and 160 kW/m² and saturated temperature of 30 °C. As a result, the surface by VPS produced higher heat transfer coefficient and lower superheat at the onset of boiling under microgravity. For the smooth surface, the effect of gravity on boiling heat transfer coefficient was a little. For the coating, a large difference in heat transfer coefficient to gravity was observed in the moderate heat flux range. The heat transfer coefficinet decreased as gravity changed from the normal to hypergravity, and was improved as gravity changed from the hyperto microgravity. The difference in heat transfer coefficient between the normal and microgravity was a little. Heat transfer enhancement factor was kept over the experimental range of heat flux. It can be said that boiling behavior on thermal spray coating might be influenced by flow convection velocity.     

Fast crystallization of poly(3‐hydroxybutyrate) and poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) with talc and boron nitride as nucleating agents

The crystallization behavior of poly(3‐hydroxybutyrate) (PHB) and poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) (PHBV) induced by two kinds of nucleating agents, boron nitride (BN) and talc, was investigated by differential scanning calorimetry, polarized optical microscopy and X‐ray diffraction. Both BN and talc have good nucleating ability in the crystallization of PHB and PHBV. From these results, combined with molecular weight measurement by gel permeation chromatography, the mechanism of nucleation by BN and talc in the crystallization of PHB and PHBV has been proposed. BN acts as a nucleating agent itself and initiates nucleation in the crystallization of PHB and PHBV. Talc acts in a different way. It reacts as a chemical reagent with the molten chains of PHB/PHBV, while the reaction product acts as the true nucleating agent, which lowers the crystallization barriers of PHB and PHBV. ¹H NMR spectroscopy provides evidence for the reaction between PHB and talc and supports the proposed nucleation mechanism. Copyright © 2005 Society of Chemical Industry     

Optimal dispersion management for a wavelength division multiplexedoptical soliton transmission system

Soliton's frequency shift arising from the pulse collision between wavelength division multiplexed (WDM) channels in an optical transmission line may be reduced by dispersion management technique. The reduction mechanism is due to a cancellation between the shifts in normal and anomalous dispersion fibers. With a proper management of the dispersion, the effect of lumped amplifiers on the frequency shift may also be canceled out. In this paper, we give a detailed analysis of the frequency shift in dispersion managed systems, and explain the reduction mechanism of the shift. We then propose optimal dispersion management schemes by means of minimizing the frequency shift. We also present a statistical analysis of the collision induced timing jitter for a two-channel WDM system