LanV, a bifunctional enzyme: aromatase and ketoreductase during landomycin A biosynthesis

LanV is involved in the biosynthesis of landomycin A. The exact function of this enzyme was elucidated with combinatorial biosynthesis by using Streptomyces fradiae mutants that produce urdamycin A. After expression of lanV in S. fradiae DeltaurdM, which is a mutant that accumulates rabelomycin, urdamycinon B and urdamycin B were found to be produced by the strain. This result indicates that LanV is involved in the 6-ketoreduction of the angucycline core, which preceeds a 5,6-dehydration reaction. 9-C-D-Olivosyltetrangulol was also produced by this strain; this demonstrates that LanV catalyses the aromatization of ring A of the angucycline structure. Coexpression of lanV and lanGT2 in S. fradiae AO, a mutant that lacks all four urdamycin glycosyltransferases, resulted in the production of tetrangulol and the glycoside landomycin H, both of which have an aromatic ring A. As glycosylated angucyclines were not observed after expression of lanGT2 in the absence of lanV, we conclude that LanGT2 needs an aromatized ring A for substrate recognition.     

Growth control of ice crystals by poly(vinyl alcohol) and antifreeze protein in ice slurries

Effect of poly(vinyl alcohol) (PVA) in inhibiting an increase in ice crystal size in isothermal ice slurries was investigated, and then compared with the effect of an antifreeze protein (AFP), NaCl, and three other polymers, namely, poly(ethylene glycol), poly(vinyl pyrrolidone), and poly(acrylic acid). First, ice slurries, in which the initial size distribution of ice crystals was known, were isothermally preserved for given periods of time (typically 300 min) in the presence of PVA, AFP type I, NaCl, or the other three polymers. Then, the average size of the ice crystals was measured using image processing. Both the PVA and AFP type I completely inhibited the increase in ice crystal size at such low concentrations that the melting temperature of the solution was , whereas NaCl and the other three polymers clearly increased the ice crystal size due to Ostwald ripening. This inhibition effect of PVA and AFP type I was caused by thermal hysteresis, which is often taken as the primary manifestation of non-equilibrium antifreeze activity of these additives and defined as the difference between the melting temperature and non-equilibrium freezing temperature at which ice crystals start to grow in solution. The increase in ice crystal size was inhibited when the thermal hysteresis surpassed the driving potential for Ostwald ripening. Using PVA, which exhibits thermal hysteresis, is a novel technique to completely inhibit the increase in ice crystal size in isothermal ice slurries.     

Design and Fabrication of a Novel Electrode-Supported Honeycomb SOFC

We report the design and fabrication of a novel electrode-supported honeycomb solid oxide fuel cell (SOFC), that can generate high volumetric power density. Among various cell designs, honeycomb SOFCs are suitable for compact SOFC modules because they have a large surface electrode area per unit volume. We have succeeded in fabricating a cathode-supported honeycomb SOFC via extrusion of a LaSrMnO₃ honeycomb monolith and through the use of a new slurry injection method for the channel surface coating using electrolyte/anode bi-layers. The fabricated honeycomb SOFCs exhibited high volumetric power densities of approximately 1.2 W/cm³ at 600°C under a wet H₂ fuel flow.     

H2O-tolerant monolithic catalysts for preferential oxidation of carbon monoxide in the presence of hydrogen

Pt–Fe/mordenite (4 wt% Pt–0.5 wt% Fe) powder catalysts were wash-coated onto ceramic straight-channel monoliths by using silica- and/or alumina-sol as a binder, and were evaluated for the preferential oxidation of carbon monoxide (PROX) in a hydrogen-rich gas. In a synthetic reformate gas (1% CO, 1% O₂, 5% H₂O, 20% CO₂, and balance H₂), the CO concentration was reduced to less than 20 ppm at temperatures ranging from 100 to 130 °C. After a certain period of the PROX reaction, condensation of H₂O in the pores of the mordenite-support occurred over the monolithic catalyst, which was wash-coated with alumina-sol, in the lower temperature range (100–120 °C), resulting in a rapid increase in CO concentration. The monolithic catalyst wash-coated with silica-sol, however, showed an excellent tolerance against H₂O condensation and offered a stable catalytic performance, maintaining a CO concentration of ca. 20 ppm for 200 h. The H₂O-tolerant characteristic was attributed to the relatively small adsorption amount of H₂O over the silica-modified monolithic catalyst.     

New Fabrication Technique for Series‐Connected Stack With Micro Tubular SOFCs

Solid oxide fuel cell (SOFC) is highly efficient and is a promising candidate for future power systems. Among the many types of SOFCs which have been reported, the micro tubular design offers improved thermal robustness, with the possibility of rapid start‐up/shut‐down. In this study, a new stack structure for anode‐supported micro tubular SOFCs was developed in which porous MgO matrices were used to position the micro tubular cell elements. This arrangement allowed for electrical interconnection of each cell in a series, using a silver paste and a connecting LSCF paste for the anode and the cathode, respectively, in the MgO support structure. With this technique, the bundle size could be easily increased towards the kW class module design.     

Wet Atomisation of Gd‐doped CeO2 Electrolyte Slurries for Intermediate Temperatures' Microtubular SOFC Applications

A wet atomising system has been employed as a novel method to prepare ultrafine Gd‐doped CeO₂ (GDC) electrolyte slurries. By changing the fluid flow pressure and repeating the atomisation process several times for the same atomised slurries, we have obtained optimised ultrafine GDC slurry with high‐dispersed and homogeneous distribution. The sizes of the particles of GDC were in the range of tens of nanometres. A highly dense electrolyte layer (membrane) was prepared using the ultrafine GDC slurries for intermediate temperatures microtubular solid oxide fuel cell (SOFC) applications. The SOFC was fabricated by using supporting porous anode tubes of NiO and GDC, and the cathode consisted of La_0.6Sr_0.4Co_0.2Fe_0.8O_3–y and GDC. A dense 10 μm GDC electrolyte layer was obtained at a lower sintering temperature of 1,250 °C for 1 h. The SOFC was tested with humidified (3% H₂O) hydrogen as a fuel and the static air as an oxidant, and the tubular cell maintained its high performance even at 500 °C.     

Application of step‐response test for evaluation of uncertainty of standard measuring system for lightning‐impulse high voltage

In evaluating the uncertainty of the standard measuring system for lightning‐impulse high voltages, which is composed of a standard voltage divider, a digital recorder, and calibrators, step‐response tests of the standard voltage divider may be useful. In this paper, a convolution algorithm is employed to calculate the output impulse voltage waveforms from measured step‐response waveforms. The uncertainties of peak‐value measurement due to the influence of the nominal epoch, uncertainty of the peak‐value measurement due to dispersion of the AC scale factor, and uncertainty of the virtual front‐time measurement due to long‐term stability are evaluated. Furthermore, the error of the virtual front time of the output waveforms is discussed. The front part of the step‐response waveform, t≤ T₃₀%, does not influence the error of the virtual front time. Therefore, for the standard voltage divider, the step‐response parameters, that is, the experimental response time, partial response time, settling time, and overshoot, have almost nothing to do with the error of the virtual front time. © 2012 Wiley Periodicals, Inc. Electr Eng Jpn, 180(2): 24–32, 2012; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.21279     

Optical Nanoscale Pool‐on‐Surface Design for Control Sensing Recognition of Multiple Cations

General design of optical chemical nanosensors is needed to develop efficient sensing systems with high flexibility, and low capital cost for control recognition of toxic analytes. Here, we designed optical chemical nanosensors for simple, high‐speed detection of multiple toxic metal ions. The systematic design of the nanosensors was based on densely patterned chromophores with intrinsic mobility, namely, “building‐blocks” onto three‐dimensional (3D) nanoscale structures. The ability to precisely modify the nanoscale pore surfaces by using a broad range of chromophores that have different molecular sizes and characteristics enables detection of multiple toxic ions. A key feature of this building‐blocks design strategy is that the surface functionality and good adsorption characteristics of the fabricated nanosensor arrays enabled the development of “pool‐on‐surface” sensing systems in which high flux of the metal analytes across the probe molecules was achieved without significant kinetic hindrance. Such a sensing design enabled sensitive recognition of metal ions up to sub‐picomolar detection limits (～10^?11 mol dm^?3), for first time, with rapid response time within few seconds. Moreover, because these sensing pools exhibited long‐term stability, reversibility and selectivity in detecting most pollutant cations, for example, Cr(VI), Pb(II), Co(II), and Pd(II) ions, they are practical and inexpensive. The key result in our study is that the pool‐on‐surface design for optical nanosensors exhibited significant ion‐selective ability of these target ions from environmental samples and waste disposals.     

Size dependence of THz region dielectric properties for barium titanate fine particles

Barium titanate (BaTiO₃) crystallites with various particle sizes from 22 to 500 nm were prepared by the two-step thermal decomposition method of barium titanyl oxalate. Various characterizations revealed that these particles were impurity-free, defect-free, dense BaTiO₃ particles. The powder dielectric measurement clarified that the dielectric constant of BaTiO₃ particles with a size of around 58 nm exhibited a maximum of over 15,000. To explain this size dependence, the THz region dielectric properties of BaTiO₃ fine particles, especially Slater mode frequency, were measured using the far infrared (FIR) reflection method. As the result, the lowest Slater mode frequency was obtained at 58 nm. This tendency was completely consistent with particle size dependence of the dielectric constant.     

Response of isotopically tailored titanium diboride to neutron irradiation

The response of polycrystalline TiB₂ to neutron irradiation was investigated. The material was fabricated using isotopically enriched ¹¹B powders to minimize helium production via the ¹⁰B(n, α)⁷Li reaction. Neutron irradiation was conducted at temperatures of ~200°C and ~600°C to a fast fluence of 2.4 × 10²⁵ n/m² (>0.1 MeV). The material exhibited some swelling, but less swelling at the higher irradiation temperature. No macroscopic damage was observed in the irradiated material, although moderate irradiation-induced micro-cracking was found in the irradiated TiB₂. This study demonstrated improved radiation resistance of isotopically tailored TiB₂ compared with natural boron TiB₂, which exhibited macroscopic fracture by irradiation.