Improvement of processability of poly(ε‐caprolactone) by radiation techniques

Improvement of processability of Poly(ε‐caprolactone) (PCL) was achieved by introduction of a branch structure using gamma‐irradiation from a ⁶⁰Co source. Irradiated PCL has higher molecular weight by producting a branch structure. Hence, the irradiation at a lower dose, such as 3 Mrad, leads to a higher melt viscosity. The branched structure gave improved properties for dynamic viscoelasticity and elongational viscosity. High elongational viscosity was observed by entanglement due to branch chain formed during irradiation, and the elongational viscosity for 3 Mrad is higher than 1.5 Mrad. Due to a higher elongational viscosity, PCL foam can be produced by a molding process. Foam produced from irradiated PCL pellets at 3 Mrad has honeycomb‐like structure, and the foam showed higher enzymatic degradation compared to film samples. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 1815–1820, 1999     

TWO-DIMENSIONAL SIMULATION IN TRANSITIONAL JET DIFFUSION FLAME WITH/WITHOUT A DUCT

The numerical study was performed to examine the dynamic structure of methane and air jet diffusion flame with and without a duct in the transitional flow regime, that is, Re = 1000-2000. The flame sheet model of infinite chemical reaction and unit Lewis number were assumed in the simulation. The temperature dependence of the viscosity and diffusivity of mixed gases was also considered. The mechanism of vortex growth was explained by using the streaklines visualized with marker particles, and the interrelation between vortical and thermal structures is clarified for two cases with and without a duct. The presence of a duct leads to suppression of vortex growth in the streamwise direction of the methane jet, and therefore the flame spreading is significantly reduced. Furthermore, oscillatory shear stress and heat flux are discussed to understand vortex-flame interactions. It is found that in the transitional flow regime, there are similarities between oscillatory momentum and heat transport inside the flame in both cases.     

Molecular cloning of the isoamyl alcohol oxidase-encoding gene (mreA) from Aspergillus oryzae

Isoamyl alcohol oxidase (IAAOD) is a novel enzyme that catalyzes the formation of isovaleraldehyde, which is the main component of mureka that gives sake an off-flavor (Yamashita et al. Biosci. Biotechnol. Biochem., 63, 1216-1222, 1999). We cloned the genomic DNA sequence encoding IAAOD from a koji mold, Aspergillus oryzae, using a PCR-amplified DNA fragment corresponding to the partial amino acid sequences of the purified protein as a probe. The cloned gene comprises 1903 bp of an open reading frame with three putative introns and encodes 567 amino acids with a presumed signal peptide consisting of 24 amino acids at the N-terminus. Moreover, nine potential N-glycosylation sites were present. Homology search on amino acid sequence showed that IAAOD has a region significantly similar to those conserved in FAD-dependent oxidoreductases. Southern hybridization analysis revealed that the cloned gene exists as a single copy in the A. oryzae RIB 40 chromosome. The cloned gene was overexpressed under the control of the amyB promoter in A. oryzae. The isovaleraldehyde-producing activity in the culture supernatant of one transformant was over 800 times as high as that of transformant with the control vector. This result demonstrates that the cloned gene encodes IAAOD. We named this novel alcohol oxidase gene "mreA".     

合金元素和显微结构对CO2/H2S环境中腐蚀产物稳定性的影响

石油天然气工业的耐蚀合金(CRAs)设计要考虑腐蚀产物的稳定性.通过电位-pH图,以及FeCO3、氧化物和硫化物溶解度的计算,评价了在CO2/H2S环境中钢铁表面生成的腐蚀产物的稳定性.在CO2的环境中,碳钢的局部腐蚀与腐蚀产物FeCO3的形成有关.含有铁素体-珠光体显微结构的J55钢可以耐CO2腐蚀,是因为层状渗碳体可以稳固表面形成的腐蚀产物.铬钢是CO2环境中的耐蚀材料,因为表面能生成黏附性非晶铬氧化物的腐蚀产物.当H2S的含量超过CO2的分压为100×10-6时的对应含量时,从腐蚀产物FeCO3和FeS的稳定性来看,其腐蚀就变成H2S的腐蚀类型.在H2S环境中,耐蚀合金腐蚀产物的稳定性与铬的氧化物和硫化物(如FeS,Ni3S2和MoS2)的生成有关.     

Surface Acoustic Waves in Reverse-Biased AlGaN/GaN Heterostructures

Properties of surface acoustic waves (SAWs) in reverse-biased AlGaN/GaN heterostructures on (0001) sapphire substrates were studied by examining the characteristics of SAW filters composed of interdigital Schottky and ohmic contacts. The fundamental and higher frequency SAW signals in measured -parameters were attributed to Rayleigh and Sezawa modes, respectively. The onsets of the SAW signals, which were close to the threshold voltage of HEMTs in the vicinities of the respective filters, changed in response to the spatial variation of the threshold voltage. The onset of Sezawa mode was deeper than that of Rayleigh mode, and the difference in onset was larger for longer SAW wavelengths. These results are possibly explained by the change of the input capacitance of interdigital transducers due to the reverse-bias voltages or by the difference in the distribution of SAW energy between the two modes.     

Novel Er and Ce codoped fluoride fiber amplifier for low-noise and high-efficient operation with 980-nm pumping

We demonstrate the low-noise and high-gain operation of a fluoride Er/sup 3+/ and Ce/sup 3+/ codoped fiber (F-ECDF) amplifier with 980-nm pumping. A 980-nm-pumped F-ECDF with a length of only 45 cm exhibits a noise figure of <4.5 dB in the entire C-band and a small signal gain of >20 dB with a gain ripple of <1 dB without any gain-flattening filter in the 1525-1560-nm range. Excitation spectra for the gain and noise figure of an F-ECDF exhibit flat shapes in the 974-982-nm range. We also demonstrate that the gain coefficient reaches 1.4 dB/mW and the power conversion efficiency is 27.4% at 1532 nm for a 2.25-m-long F-ECDF.     

Mechanism of Ca2+ increase in myoblasts derived from chicken embryos

The mechanism of intracellular calcium ions (Ca(2+)) increase in chicken myoblasts was studied using histological, immunohistochemical, immunoblotting and Ca(2+) imaging techniques. Mononuclear myoblasts at embryonic day 12 (E12) contained myofibrils in the peripheral cytoplasm, and the sarcoplasmic reticulum was observed in the cytoplasm. Several Ca(2+)-related receptors, namely acetylcholine (ACh) receptors, dihydropyridine receptors (DHPRs) and ryanodine receptors (RyRs), were detected in the tissue as early as E12. Western blotting analyses detected one band corresponding to RyR subtype 3 (RyR3) at E12 and two bands corresponding to RyR1 and RyR3 after E13. Ca(2+) imaging of mononuclear myoblasts in vitro revealed an intense Ca(2+)-increase response to ACh stimulation, and this effect was abolished after EGTA addition to the culture medium. Nifedipine treatment also led to a lack of Ca(2+) increase in response to ACh stimulation, while ryanodine treatment led to a weak Ca(2+)-increase response. On the other hand, multinuclear myoblasts showed a Ca(2+)-increase response to ACh stimulation in the presence of not only EGTA but also nifedipine, although ryanodine treatment led to a lack of Ca(2+) increase. These results suggest that the mechanism of Ca(2+) increase in mononuclear myoblasts involves extracellular Ca(2+) entry through DHPRs, which is amplified by Ca(2+) release from the cytoplasmic Ca(2+) store, while multinuclear myoblasts mainly depend on Ca(2+) release from the cytoplasmic Ca(2+) store.     

Effects of siRNAs targeting the spacer sequence of plant RNAi vectors on the specificity and efficiency of RNAi

Small interfering RNAs (siRNAs) generated from the spacer region of hairpin RNAs were not detected in the RNA interference (RNAi) plants targeting the fatty acid desaturase gene. The expression of the desaturase gene was stably suppressed even when siRNAs targeting the spacer sequences were introduced into this plant.     

Structural and magnetic properties of Lix(MnyFe1−y)PO4 electrode materials for Li-ion batteries

A series of LiMn_yFe_1−yPO₄ samples have been prepared in the whole range 0 ≤ y ≤ 1. Chemical delithiation could be achieved to obtain Mn_yFe_1−yPO₄ in the range 0 ≤ y ≤ 0.8, keeping the same crystal phase (olivine structure, space group Pnma). The composition y = 0.8 is the limit where the delithiated phase is still crystallized, but abruptly suffers strains at the molecular scale evidenced by both optical spectroscopy and X-ray diffraction. The analysis of the magnetic properties shows that in all the samples the concentration of impurities is negligible. The concentration of polarons, either holes associated to Li vacancies in LiMn_yFe_1−yPO₄ or electrons associated to the existence of Li left in the matrix of Mn_yFe_1−yPO₄, is found to be small (≤1%) in all the samples. For y ≤ 0.6, all the Mn³⁺ ions Mn_yFe_1−yPO₄ are in the high-spin state (S = 2). At larger manganese concentration, however, the Mn³⁺ ions in excess of the critical concentration y_c = 0.6 undergo a transition to the low-spin state (S = 1). As a consequence, and in contrast with prior works, we find that Mn_0.8Fe_0.2PO₄ has magnetic interactions that are much smaller, and no antiferromagnetic ordering in this compound is detected, at least above 20 K. Antiferromagnetic ordering that had been reported so far for Mn_yFe_1−yPO₄ at large y-composition might come from incomplete delithiation. The spin-transition of Mn³⁺ in concentration (y–y_c) to the low-spin state is at the origin of the strain fields at the molecular scale that increase with y for y > 0.6, and ultimately prevents the full delithiation for y > 0.8. This result sheds light on the reason for the degradation of cathode properties in Mn-rich compounds of the heterosite–purpurite series, while the electrochemical properties are good in the range y ≤ 0.6 but only at slow rates, due to the very small hopping mobility of the small polaron.     

Isolation of Solid Solution Phases in Size‐Controlled LixFePO4 at Room Temperature

State‐of‐the‐art LiFePO₄ technology has now opened the door for lithium ion batteries to take their place in large‐scale applications such as plug‐in hybrid vehicles. A high level of safety, significant cost reduction, and huge power generation are on the verge of being guaranteed for the most advanced energy storage system. The room‐temperature phase diagram is essential to understand the facile electrode reaction of Li_xFePO₄ (0 < x < 1), but it has not been fully understood. Here, intermediate solid solution phases close to x = 0 and x = 1 have been isolated at room temperature. Size‐dependent modification of the phase diagram, as well as the systematic variation of lattice parameters inside the solid‐solution compositional domain closely related to the electrochemical redox potential, are demonstrated. These experimental results reveal that the excess capacity that has been observed above and below the two‐phase equilibrium potential is largely due to the bulk solid solution, and thus support the size‐dependent miscibility gap model.