Reinvestigation of the Oxidative Folding Pathways of Hen Egg White Lysozyme: Switching of the Major Pathways by Temperature Control

It has been well established that in the oxidative folding of hen egg white lysozyme (HEL), which has four SS linkages in the native state (N), three des intermediates, i.e., des[76–94], des[64–80], and des [6–127], are populated at 20 °C and N is dominantly formed by the oxidation of des[64–80] and des[6–127]. To elucidate the temperature effects, the oxidative folding pathways of HEL were reinvestigated at 5–45 °C in the presence of 2 M urea at pH 8.0 by using a selenoxide reagent, DHS^ox. When reduced HEL was reacted with 1–4 equivalents of DHS^ox, 1S, 2S, 3S, and 4S intermediate ensembles with 1–4 SS linkages, respectively, were produced within 1 min. After the oxidation, 3S was slowly converted to the des intermediates with formation of the native structures through SS rearrangement. At 5 °C, des[76–94] was populated in the largest amount, but the oxidation to N was slower than that of des[64–80] and des[6–127]. At 35 °C, on the other hand, des[64–80] and des[6–127] were no longer stable, and only des[76–94] was populated. The results suggested that the major folding pathways of HEL can be switched from one to the other by temperature control.     

Dramatic Enhancement of Photoluminescence Quantum Yields for Surface‐Engineered Si Nanocrystals within the Solar Spectrum

Substantial improvements of the absolute photoluminescence quantum yield (QY) for surfactant‐free silicon nanocrystals (Si‐ncs) by atmospheric pressure microplasma 3‐dimensional surface engineering are reported. The effect of surface characteristics on carrier multiplication mechanisms is explored using transient induced absorption and photoluminescence QY. Surface engineering of Si‐ncs is demonstrated to lead to more than 120 times increase in the absolute QY (from 0.1% up to 12%) within an important spectral range of the solar emission (2.3–3 eV). The Si‐ncs QY is shown to be stable when Si‐ncs are stored in ethanol at ambient conditions for three months.     

Temperature influence on performance degradation of hydrogenated amorphous silicon solar cells irradiated with protons

This paper reports temperature influence on radiation degradation of hydrogenated amorphous silicon (a‐Si : H) solar cells. Degradation behaviors of a‐Si : H solar cells irradiated with protons at 331 K are compared with that at 298 K (room temperature). Variations with time in the post‐irradiation electrical properties are also investigated. It is found that the radiation degradation of the electrical properties at 331 K is significantly smaller than that at room temperature. Also, all the electrical properties (short‐circuit current, open‐circuit voltage, output maximum, and fill factor) recover with time after irradiation even at room temperature. The characteristic time of thermal annealing of short‐circuit current is larger as the temperature is higher. These results indicate that temperature during irradiation and elapsed time from irradiation to measurement is an important parameter for radiation degradation of a‐Si : H solar cells. Therefore, these parameters should be controlled in conducting the ground radiation tests. Copyright © 2012 John Wiley & Sons, Ltd.     

Numerical analysis of double-diffusive convection in a porous enclosure due to opposing heat and mass fluxes on the vertical walls – Why does peculiar oscillation occur?

Peculiar oscillating convection is observed when two-dimensional double-diffusive convection in porous medium is analysed numerically. The top and bottom walls of an enclosure are insulated, and constant and opposing heat and mass fluxes are prescribed on the vertical walls. The peculiar oscillations are of three types: (1) Chaotic oscillations wherein the main flow is due to temperature; however, the convection due to concentration is strong enough to generate this peculiar oscillation. (2) The ‘sudden steady state case’ caused by the shifts from thermally-driven to concentration-driven forces. (3) The ‘re-oscillation case’ caused by the convection pattern changes from centrosymmetric to non-centrosymmetric.     

High-frequency Lamb wave device composed of MEMS structure using LiNbO3 thin film and air gap

High-frequency devices operating at 3 GHz or higher are required, for instance, for future 4th generation mobile phone systems in Japan. Using a substrate with a high acoustic velocity is one method to realize a high-frequency acoustic or elastic device. A Lamb wave has a high velocity when the substrate thickness is thin. To realize a high-frequency device operating at 3 GHz or higher using a Lamb wave, a very thin (less than 0.5 μm thick) single-crystal plate must be used. It is difficult to fabricate such a very thin single crystal plate. The authors have attempted to use a c-axis orientated epitaxial LiNbO(3) thin film deposited by a chemical vapor deposition system (CVD) instead of using a thin LiNbO(3) single crystal plate. Lamb wave resonators composed of a interdigital transducer (IDT)/the LiNbO(3) film/air gap/base substrate structure like micro-electromechanical system (MEMS) transducers were fabricated. These resonators have shown a high frequency of 4.5 and 6.3 GHz, which correspond to very high acoustic velocities of 14,000 and 12,500 m/s, respectively, have excellent characteristics such as a ratio of resonant and antiresonant impedance of 52 and 38 dB and a wide band of 7.2% and 3.7%, respectively, and do not have spurious responses caused by the 0th modes of shear horizontal (SH(0)) and symmetric (S(0)) modes.     

Effect of Hydrogen Atmosphere on Pyrolysis of Cured Polycarbosilane Fibers

SiC-based fibers with various chemical compositions were synthesized using an irradiation-curing process. Polycarbosilane (PCS) fibers were cured by irradiation with an electron beam in a helium atmosphere. The cured PCS fibers were pyrolyzed at 1300°C under controlled hydrogen or argon atmospheres, and SiC fibers with C/Si of 0.84 to 1.56 were obtained. The fibers consisted of <1.0 wt% O, <0.2 wt% N, <0.1 wt% H, with the balance being Si and C. The mechanism of pyrolytic transformation of cured PCS to SiC-based ceramics was investigated using TG/DTA analysis. Greater mass losses were observed during pyrolysis in a hydrogen atmosphere than in argon. This result suggests that the hydrogen atmosphere suppresses H₂ evolution and helps to remove excess carbon as CH₄ during pyrolysis. The microstructure and mechanical properties of the resulting SiC-based fibers were found to be very dependent on their C/Si chemical compositions.     

Photoluminescence Analysis of Iron Contamination Effect in Multicrystalline Silicon Wafers for Solar Cells

We investigated the effect of Fe contamination on the electronic properties of dislocation clusters in relation to oxygen precipitation in multicrystalline silicon (mc-Si). Photoluminescence (PL) spectroscopy and mapping were performed at room and liquid-He temperatures on mc-Si wafers before and after Fe contamination. PL spectra consisted of the band-edge emission, the 0.78-eV emission associated with oxygen precipitates, and the dislocation-related D-lines. The Fe contamination increased the electrically active dislocation clusters. Part of these clusters acted as preferential oxygen precipitation sites, and their electronic properties were not further influenced by the Fe contamination.     

Formation and Microstructure of Carbon-Containing Oxide Scales by Oxidation of Single Crystals of Zirconium Carbide

The isothermal oxidation of ZrC single crystals with (100) orientation was carried out at temperatures of 500°, 550°, and 600°C at an oxygen pressure of 2.6 kPa for times up to 240 h. A polished cross section of the oxidized crystal was observed by backscattered electron imaging in a scanning electron microscope. Quantitative chemical analysis for Zr, O, and C and their elemental profiles by the linescan method in the ZrC and oxide scale were performed by wavelength dispersive X-ray microanalysis. A thin foil of a crystal oxidized at 600°C was examined by transmission electron microscopy. It was found that the oxide scale was divided into two regions, zones 1 and 2, which contained 14 to 23 and 7 to 10 at. % carbon, respectively. Zone 1 exhibited an almost compact, pore-free matrix of c -ZrO₂. In zone 2, some growth and aggregation of the c -ZrO₂ occurred, producing 5- to 20-nm-sized particles between which carbon should have been present. The thickness of zone 1 increased parabolically up to 240 h at 500°C and probably in an early period at 550° and 600°C, reaching a constant (about 2 (μm), in contrast to the thickness of zone 2, which increased linearly with time.     

The failure mechanism and the pull-out strength of a bond-type anchor near a free edge

A bond-type anchor bolt has been used as a post-installed type anchor. Recent developments in construction technology have diversified the use of this type of anchor even in a new construction site. Since this type of anchor exhibits a complex failure mode involving cone and bond failure, its design method is still to be investigated in depth. Among the various conditions to be considered, we focus on the effect of a free edge on the pull-out strength both experimentally and analytically. We propose a new method to estimate the cone failure strength using the theory of linear fracture mechanics. The experimental results coincide well with the analytical estimation. The reduction of the strength is much larger than expected by the analysis based on the current design method.