Influence of macromolecular structure of novel 2- and 4-armed polylactides on their physicochemical properties and in vitro degradation process

The objective of this study was to analyse how macromolecular structure of polylactides influences their properties and degradation rate. To achieve this, novel 2- and 4-armed PDLLA and PLLA (noted as 2b and 4b) were synthesized by ring-opening method. 1,4-butanediol and pentaerythritol were used as initiators and stannous octoate was used as catalyst. The obtained polymers were investigated in terms of molecular weight by size exclusion chromatography, thermal properties by differential scanning calorimetry and thermogravimetry, and hydrophilicity by the contact angle measurements. The in vitro degradation test was carried out in PBS solution at 37 °C by means of the mass loss, water uptake, molecular weight and thermal properties changes. The branched polylactides including 2bPDLLA, 4bPDLLA, 2bPLLA and 4bPLLA were successfully synthesized and the average molecular weights were around 40-45 kDa. The numbers of arms in each polymer just slightly influenced the thermal properties and the contact angle. The crystallinity of 4bPLLA was 23 %, whereas for 2bPLLA it was 41 %. The degradation rates of both 2b and 4bPLLA were similar and the degradation process was similar only during first 7 weeks. After this period, the degradation rate of 4bPDLLA increased. Consequently, thermal properties and degradation profiles of the branched polymers would depend on plural factors, such as chain length and crystallinity in branched structure.     

Preparation of Yttria-Stabilized Zirconia Thin Films on Strontium-Doped LaMnO3 Cathode Substrates via Electrophoretic Deposition for Solid Oxide Fuel Cells

A yttria-stabilized zirconia (YSZ) thin film on an La_0.8Sr_0.2MnO₃ porous cathode substrate was prepared, using electrophoretic deposition (EPD) to fabricate a solid oxide fuel cell (SOFC). The electrical conductivity of an La_0.8Sr_0.2MnO₃ substrate is satisfactorily high at room temperature; therefore, YSZ powder could be deposited electrophoretically onto an La_0.8Sr_0.2MnO₃ substrate without any extra surface treatment, such as a metal coating. Successive repetition of EPD and sintering was required to obtain a film without gas leakage, because of the thermal expansion coefficient mismatch between the YSZ and the La_0.8Sr_0.2MnO₃ substrate. On the other hand, the electromotive force of the oxygen concentration in the cell that used YSZ film prepared via EPD increased and attained the theoretical value when the number of deposition and calcination cycles was increased. Six or more successive repetitions were required to obtain a YSZ film without gas leakage. A planar-type SOFC was fabricated, using nickel as the anode and YSZ film (∼10 μm thick) that had been deposited onto the La_0.8Sr_0.2MnO₃ substrate as the electrolyte and cathode. The cell exhibited an open circuit voltage of 1.0 V and a maximum power density of 1.5 W/cm². Thus, the EPD method could be used as a colloidal process to prepare YSZ thin-film electrolytes for SOFCs.     

Dynamic viscoelastic behavior of cholesteric liquid crystalline side-chain copolymers

Summary The rheological behavior of the cholesteric side-chain copolysiloxane whose two kinds of mesogenic groups consist of cholesteryl units and biphenyl benzoate units was investigated for three different compositions: 31:69, 35:65, 37:63 (in mol%). On the frequency dependence diagram of G′ for the copolymers at various temperatures, G′ decreases with decreasing frequency. The slope of G′ in a higher frequency region at lower temperatures (110°–130°C) is similar to that in the flow region of amorphous polymer melts. However, the slope of G′ in a lower frequency region at higher temperatures (140°–160°C) is relatively small, and the G′ curves in this region can not be superposed on to a single master curve. This deviation seems to be due to change in stability of the domain structure of the cholesteric phase. Furthermore, on the temperature dependence curve of G′, G′ showed a maximum near T _c1 . This maximum of G′ curve seems to be caused by molecular organization of a blue phase.     

Minor actinide transmutation in fast reactor metal fuels irradiated for 120 and 360 equivalent full-power days

An irradiation experiment on uranium–plutonium–zirconium (U–Pu–Zr) alloys containing 5 wt% or less minor actinides (MAs) and rare earths was carried out in the Phénix fast reactor. The isotope compositions of the fuel alloys irradiated for 120 and 360 equivalent full-power days (EFPDs) were chemically analyzed by inductively coupled plasma–mass spectrometry after 3.3–5.3 years of cooling. The results of chemical analysis indicated that the discharged burnups of the fuel alloys irradiated for 120 and 360 EFPDs were 2.1–2.5 and 5.3–6.4 at%, respectively. The changes in the isotopic abundances of plutonium, americium, and curium during the irradiation experiment were assessed to discuss the transmutation performance of MA nuclides added to U–Pu–Zr alloy fuel. Multigroup three-dimensional diffusion and burnup calculations accurately predicted the changes in these isotopic abundances after fuel fabrication. An evaluation of the MA transmutation ratio based on the results of chemical analysis revealed that the quantity of MA elements in the U–19Pu–10Zr–5MA (wt%) alloy decreased by about 20% during the irradiation experiment for 360 EFPDs.     

Material-binding peptide application--ZnO crystal structure control by means of a ZnO-binding peptide

Recently, a zinc oxide (ZnO)-binding peptide (ZnOBP) has been identified and has been used to assist the synthesis of unique crystalline ZnO particles. We analyzed the influence of ZnOBP on the crystal growth of ZnO structures formed from zinc hydroxide. The addition of ZnOBP in the hydrothermal synthesis of ZnO suppressed [0001] crystal growth in the ZnO particles, indicating that the specificity of the material-binding peptide for specific inorganic crystal faces controlled the crystal growth. Furthermore, the dipeptides with a partial sequence of ZnO-binding "hot spot" in ZnOBP were used to synthesize ZnO particles, and we found that the presence of these dipeptides more strictly suppressed (0001) growth in ZnO crystals than did the complete ZnOBP sequence. These results demonstrate the applicability of dipeptides selected from material-binding peptides to control inorganic crystal growth.     

Controlled reduction of Cu to Cu with an N,O-type chelate under hydrothermal conditions to produce Cu2O nanoparticles

N,O-type organic chelates reduced coordinated Cu²⁺ ions under hydrothermal reaction conditions to produce Cu₂O/CuO nanoparticles. Chelates in which the N and O atoms are closely spaced produced smaller amounts of CuO nanoparticles, indicating their higher ability to reduce Cu²⁺ ions to Cu⁺ ions. [Cu(Gly)₂]² with the shortest ligand chain length produced only Cu₂O nanoparticles and, therefore, can be used as a single molecule precursor for the synthesis of Cu₂O nanoparticles.     

Phase relations in the Fe-Pu-U ternary system

An isothermal section of the Fe-Pu-U ternary system at 650 °C was assessed in a previous study. In the present study, the predictions of the phase relations in the Fe-Pu-U system to higher and lower temperatures were performed by applying the interaction parameters determined at 650 °C. Differential thermal analysis (DTA) for the Fe-Pu-U alloys was also carried out to confirm the phase relations in the temperature region of 500 to 800 °C. Both results agreed well. On the basis of the predicted ternary phase diagram, the phase relations for a region surrounded by Fe₂Pu, Fe₂U, U, and Pu were described by a reaction scheme and a projection of the liquidus surface.     

Phase transition and the packing structure of the side mesogenic groups of liquid crystalline side-chain copolymers

Summary Copolymers consisting of cholesteryl 11-methacryloyloxy-undecanoate (ChMO-10) and t-buthyl methacrylate (t-BMA) were studied by DSC method and by small angle X-ray scattering method (SAXS). Although homopolymer (pChMO-10) has two different packing structures which are a single-layer packing structure and a two-layer packing one, copolymers (co-pChMO-10-t-BMA) have only the single layer packing one in their mesophase. Furthermore, transition entropy at a clearing point of co-pChMO-10-t-BMA (80/20) is larger than that of pChMO-10. Adequate distance of the mesogenic groups in the direction of a short axis of the mesogenic groups, produced by introduction of non-mesogenic units, seems to stabilize the single-layer packing structure.     

Effect of oxide species and thermomechanical treatments on the strength properties of mechanically alloyed Fe-17%Cr ferritic ODS materials

The effects of several oxide species, such as Y₂0₃, Zr0₂ and MgO, and the thermomechanical treatment (TMT) after the mechanical alloying (MA) process on the strength properties of Fe-17%Cr ferritic ODS (oxide dispersion strengthening) MA materials were investigated. Y20, showed the most uniform dispersion of the finest particles among me above oxides, but the microstructural evolution during the TMT had a larger effect on the strengthening of the alloys than the fine and uniform dispersion of the Y₂O₃ particles had.     

Evaluation tests of 1700 °C class turbine cooled blades for a hydrogen fueled combustion turbine system

The development of 1700 °C class hydrogen fueled combustion turbine system with output of 500 MW and thermal efficiency of over 60% (HHV) has been conducted in the World Energy Network (WE‐NET) program. This paper describes the development of the first‐stage turbine cooled stator and rotor blades applied to the power generation system. The conceptual design of these cooling blades which were served in hot steam flow was carried out. The hybrid cooling method combining recovery cooling with partial ejection cooling was chosen from several cooling systems from a viewpoint of plant efficiency, operational reliability, and durability of cooled blades. Also, the single crystal superalloy (SC) as a blade substrate and thermal barrier coating (TBC) were applied. The experiments of the scale model turbine cooled blades were carried out using a hydrogen–oxygen combustion wind tunnel with practical steam conditions of 1700 °C and 2.5 MPa. The cooling effectiveness and metal temperature at rated condition and the soundness of TBC and blade substrate of the first stage stator and rotor test blades were clarified. © 2003 Wiley Periodicals, Inc. Heat Trans Asian Res, 32(3): 237–252, 2003; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.10088