Synthesis of Highly Oriented Lithium Niobate Thin Film from Neutralized Aqueous Precursor Solution

Lithium niobate thin films with a c -axis orientation were synthesized from a neutralized aqueous precursor solution that was derived from lithium niobium double alkoxide. Lithium niobium hydroxide solution that was prepared by dissolving precipitates, through the complete hydrolysis of lithium niobium double alkoxide with water, was weakly basic. The hydroxide solution was neutralized with acetic acid to give neutralized homogeneous lithium niobium hydroxide solution. The film that was prepared at 500°C from the neutralized precursor solution had a smooth surface texture without cracks and pores. A pole-figure pattern indicated that the crystalline film was twinned, with rotation by 60° oriented along the c -axis.     

Processing of Novel Strontium Titanate-Based Thin-Film Varistors by Chemical Solution Deposition

Strontium titanate (SrTiO₃)-based multilayered film with varistor characteristics has successfully been fabricated by a chemical solution deposition (CSD) method. Homogeneous precursor solutions of SrTiO₃ and Nb:SrTiO₃ with long-term stability could be prepared by optimizing the reaction conditions among strontium ethoxide, titanium isopropoxide, and niobium ethoxide. Films were prepared using the precursor solutions on fused silica substrates at 700°C. Triple layered films with SrTiO₃/Nb:SrTiO₃/SrTiO₃ structure were also successfully crystallized on Pt/Ti/SiO₂/Si substrates at 700°C. The current–voltage ( I - V ) curve of the multilayered film was characteristic to varistors and the nonlinear coefficient α of the synthesized film was ∼3.0. The varistor voltages ( E _0.01) of 0.6-μm-thick film were 140 kV/cm for the forward direction and −120 kV/cm for the reverse direction, respectively, at room temperature.     

Exact Algorithms for the Bottleneck Steiner Tree Problem

Given n points, called terminals, in the plane ℝ² and a positive integer k, the bottleneck Steiner tree problem is to find k Steiner points from ℝ² and a spanning tree on the n+k points that minimizes its longest edge length. Edge length is measured by an underlying distance function on ℝ², usually, the Euclidean or the L ₁ metric. This problem is known to be NP-hard. In this paper, we study this problem in the L _p metric for any 1≤p≤∞, and aim to find an exact algorithm which is efficient for small fixed k. We present the first fixed-parameter tractable algorithm running in f(k)⋅nlog ² n time for the L ₁ and the L _∞ metrics, and the first exact algorithm for the L _p metric for any fixed rational p with 1<p<∞ whose time complexity is f(k)⋅(n ^k +nlog n), where f(k) is a function dependent only on k. Note that prior to this paper there was no known exact algorithm even for the L ₂ metric.     

Transient shift of local oxygen potential in nonstoichiometric oxides upon application of mechanical stress

Effect of mechanical stress on defect equilibrium was studied with an oxygen nonstoichiometric compound, La_0.6Sr_0.4Co_0.2Fe_0.8O_3-δ . In general, formation of oxygen vacancy in an oxide causes lattice expansion, which leads to stabilization of oxygen vacancy in the material under a tensile stress, and vice versa. Oxygen vacancy concentration is thus expected to increase under a tensile stress and decrease under a compressive stress. However, the change in defect concentration would not proceed spontaneously so that the material just after the application of stress would stay out of equilibrium. On this assumption, attempts were made to detect the shift of oxygen potential under stress using a potentiometric method. A ball-shaped yttria stabilized zirconia (YSZ) of 9.5 mm in diameter was utilized as an oxygen potential sensor as well as a pushing rod which was pressed onto the sample surface. In the measurements at 873 K to 1073 K, a clear shift of emf to the negative direction was observed depending on the magnitude of load and loading speed. It was followed by a relaxation to the initial value under the stress. On unloading operation, the shift of emf to the positive direction was observed. Those behaviors were well explained by the assumption that the oxygen vacancy concentration varies under mechanical stress.     

Nanogel bottom-up gel biomaterials for protein delivery: Photopolymerization of an acryloyl-modified polysaccharide nanogel macromonomer

Polysaccharide nanogels are one of the most attractive carriers for drug delivery systems. Nanogels encapsulate proteins in their hydrated polymer networks, and minimize the denaturation of proteins. In this study, we demonstrated the cross-linking of acryloyl group-modified polysaccharide nanogels via photopolymerization, which allowed the formation of novel hydrogel particles and macrogels. The mechanical properties of the resultant hydrogels depended on the concentrations of the nanogels and the cross-linkers. The most significant property of the nanogel-cross-linked hydrogel was the ability to encapsulate insulin via hydrophobic interactions. After incubation of the hydrogel containing insulin in water, the hydrogel was degraded by hydrolysis, and insulin was gradually released from the hydrogels over a period of 1 week. According to these results, this nanogel-cross-linked hydrogel prepared via photopolymerization has potential for innovative biomaterials.     

Thin anodic oxides on n-InP studied by photocurrent transients and surface analysis

Surface reactions induced by fluorocarbon plasmas were studied on Si substrates with SiO₂ and photo-resist overlayers using an inductively coupled plasma source. As source gases, C₄F₈ and C₅F₈ were employed to investigate their differences in the etching performance and the selectivity between SiO₂ and photo-resist. Deposition of fluorocarbon polymer was noticed in both gases by Fourier-transform infrared ellipsometric measurements when substrate bias was not applied. With the bias application, etching started on both substrate from certain threshold values of the bias voltage and the rate increased with increase of the voltage. However, in C₅F₈ plasma the increasing tendency on photo-resist was much less than on SiO₂, while in C₄F₈ plasma the difference is small. This difference is attributed to a larger deposition ability of C₅F₈ plasma with higher content of fluorine atoms in the polymer than that of C₄F₈ plasma as confirmed by X-ray photoelectron spectroscopy.     

Size and surface modification of amorphous silica particles determine their effects on the activity of human CYP3A4 in vitro

Because of their useful chemical and physical properties, nanomaterials are widely used around the world - for example, as additives in food and medicines - and such uses are expected to become more prevalent in the future. Therefore, collecting information about the effects of nanomaterials on metabolic enzymes is important. Here, we examined the effects of amorphous silica particles with various sizes and surface modifications on cytochrome P450 3A4 (CYP3A4) activity by means of two different in vitro assays. Silica nanoparticles with diameters of 30 and 70 nm (nSP30 and nSP70, respectively) tended to inhibit CYP3A4 activity in human liver microsomes (HLMs), but the inhibitory activity of both types of nanoparticles was decreased by carboxyl modification. In contrast, amine-modified nSP70 activated CYP3A4 activity. In HepG2 cells, nSP30 inhibited CYP3A4 activity more strongly than the larger silica particles did. Taken together, these results suggest that the size and surface characteristics of the silica particles determined their effects on CYP3A4 activity and that it may be possible to develop silica particles that do not have undesirable effects on metabolic enzymes by altering their size and surface characteristics.     

Transient phenomena in a PEMFC during the start-up of gas feeding observed with a 97-fold segmented cell

To measure local phenomena in a PEMFC during a transitional state induced by changing of the feeding gas, a segmented cell was fabricated and the local current and local potential distribution were measured under open-circuit conditions. The anode or cathode was divided into 97 segments of 1.5 mm each. A change in the anode gas from nitrogen or oxygen to hydrogen induced momentary internal currents among the segments. The potential distribution in the electrolyte was observed simultaneously using three quasi-reference electrodes located locally. The results supported the reverse-current decay mechanism, which is known to be a mechanism of cathode degradation. Furthermore, internal currents were observed when the cathode gas was changed from nitrogen to oxygen. While the cathode was not subjected to a harmful potential, a large potential distribution was induced in the anode.