Study on quantitative classification of seasonal snow using specific surface area and intrinsic permeability

The release mechanism of snow avalanches depends on the mechanical properties of snow, which are closely related to snow microstructure. Previous observations show that snow microstructure can be described qualitatively on the basis of snow types. However, the qualitative determination of snow types may become subjective. Therefore, it is essential to quantitatively classify snow. The specific surface area (SSA) and intrinsic permeability (k₀) are closely related to the snow microstructure. In particular, we believe that the former parameter reflects the features of the grains, and the latter parameter indicates the characteristics of the pores. Measurements of the specific surface area per unit snow volume (SSAV) and the intrinsic permeability were performed on the naturally deposited dry snow in Hokkaido prefecture, Japan, during the winter of 2007–2008. SSAV was measured using a stereological method, where the section planes of snow samples were prepared, imaged, and analyzed, and the SSA per unit mass (SSAM) was obtained by dividing SSAV by the snow density. The value of SSAV indicates only the area size, while the value of SSAM indicates the snow microstructure. k₀ was measured in situ using an air permeameter with a double cylinder, and it was calculated assuming a laminar flow in order to satisfy Darcy's law. The results showed that the correlation between SSAM and k₀ could be used to clearly distinguish the snow types. In addition, we could confirm certain changes in SSAM and k₀ accompanied by the occurrence of the two processes of temperature gradient and melt-freezing metamorphism, which occur in the snow cover.     

Synthesis of hollow silica microparticles from bacterial templates

Hollow inorganic particles have attracted great interest because of their unique physicochemical properties. In this study, hollow silica microparticles were prepared using a rod-shaped gram-negative bacterium, Escherichia coli (KP7600), as a biological template. Silica nanoparticles were generated in addition to coated biological templates when the reaction rate was increased, so control of reaction rate is important for coating silica smoothly onto the bacterial surface. Silica coating was also carried out using the fixed cells (with and without internal water) using glutaraldehyde as templates. When the fixed cells without internal water were used as templates, no rod-shaped particles were observed after calcination of the synthesized particles. By contrast, silica hollow particles were formed using the fixed cells with internal water as templates. This means that the internal water inside biological cells acts as an initiator for hydrolysis of tetraethyl orthosilicate (TEOS) and results in the formation of smooth silica shell surface and indicates that the use of dry cultured bacteria templates is not required. Thus, there is a significant benefit in using gram-negative bacteria as templates for producing hollow silica microparticles, compared with the method using dried gram-positive bacteria templates.     

Large enhancement of fluorescence efficiency from CdSe/ZnS quantum dots induced by resonant coupling to spatially controlled surface plasmons

Nanoengineered fluorescent response is reported from semiconductor core-shell (CdSe/ZnS) quantum dots in proximity to the surface plasmon polariton field of periodic Ag nanoparticle arrays. Tuning the surface plasmon polariton resonance to the quantum dot exciton emission band results in an enhancement of up to approximately 50-fold in the overall fluorescence efficiency, in a design where each Ag nanoparticle is interconnected by a continuous Ag thin film. Propagating modes of surface plasmon resonances have a direct impact on the fluorescence enhancement.     

Synthesis of hollow zirconia particles using wet bacterial templates

Hollow particles have attracted considerable attention owing to their unique properties. In this work, hollow zirconia particles were synthesized using rod-shaped gram-negative bacteria, Escherichia coli, as templates. A zirconia precursor, generated by the hydrolysis of zirconium butoxide, was deposited on the surface of the bacterial cells to form the shell of the hollow particles. The as-synthesized particles had the morphology of the bacterial templates, and were about 1.7 μm long and 0.8 μm across. The bacterial templates could be removed by calcination at 800 °C. The particles shrank on calcination to a final size of about 1.0 μm long and 0.4 μm across, with a wall thickness of about 69 nm. The specific surface area and average pore diameter were 45.7 m²/g and 1.9 nm, respectively. When fixed cells without internal water were used as templates, no hollow particles were observed; this implies that the internal water inside the cells acted as the initiator for the hydrolysis of zirconium butoxide.     

Hydrothermal synthesis and properties of solid solutions and composite nanoparticles in the TiO2-SnO2 system

Solid solutions and composite nanoparticles in the TiO₂-SnO₂ system were directly formed via the hydrothermal treatment of precursor solutions of TiCl₄ and SnCl₄ under weakly basic conditions in the presence of urea. The rutile-type (Ti, Sn)O₂ solid solutions were formed in the composition range of Ti 0-70 mol%. The composite nanoparticles consisting of anatase- and rutile-type phases were formed at the composition of Ti 80 and Ti 90 mol%. The change in the lattice parameters a₀ and c₀ of the rutile-type solid solutions followed the Vegard Law. The crystallite size of the rutile-type solid solutions was in the range of 5-10 nm. The diffuse reflectance spectra varied with changing Ti content in the precipitates. The photocatalytic activity of composite nanoparticles synthesized at 240 °C was higher than that synthesized at 180 °C. The composite nanoparticles consisting of anatase- and rutile-type phases with compositions Ti_0.90Sn_0.10O₂ and Ti_0.80Sn_0.20O₂ showed improved photocatalytic activity.     

Definition of an Index Parameter To Screen Highly Functional Enzymes Derived from a Biochemical and Thermodynamic Analysis of Ancestral meso-Diaminopimelate Dehydrogenases

Sequence-based protein design approaches are being adopted to generate highly functional enzymes; however, screening the enzymes remains a time-consuming task. In this study, by analyzing the enzymatic properties of four ancestral meso-2,6-diaminopimelate dehydrogenases (AncDAPDHs), AncDAPDH-N1, -N2, -N3, and -N4, we attempted to define a new index parameter that is helpful for efficiently screening the enzymes. Biochemical and thermodynamic analyses indicated that only AncDAPDH-N4 exhibited greater thermal stability than and activity similar to those of native DAPDHs. Structural and sequence comparisons between DAPDH from Corynebacterium glutamicum (CgDAPDH) and the AncDAPDHs suggested that “quality of mutations” is a potential index parameter. In fact, the mutations introduced from CgDAPDH to AncDAPDH-N4 correlated highly with the mutations accumulated during the evolution process from mesophiles to thermophiles. These results suggest that, although there are several exceptions, the correlation coefficient can be used as an index parameter for screening high-functioning enzymes from sequence data.