Step-bunching instability of growing interfaces between ice and supercooled water.

SignificanceStep-bunching instability (SBI) is one of the interfacial instabilities driven by self-organization of elementary step flow associated with crystal-growth dynamics, which has been observed in diverse crystalline materials. However, despite theoretical suggestions of its presence, no direct observations of SBI for simple melt growth have been achieved so far. Here, with the aid of a type of optical microscope and its combination with a two-beam interferometer, we realized quantitative in situ observations of the spatiotemporal dynamics of the SBI. This enables us to examine the origin of the SBI at the level of the step-step interaction. We also found that the SBI spontaneously induces a highly stable spiral growth mode, governing the late stage of the growth process.

Two-Dimensional Structures Formed by Triblock Patchy Particles with Two Different Patches.

Two-dimensional structures formed by spherical triblock patchy particles are examined by performing Monte Carlo simulations. In the model, the triblock patchy particles have two different types of patches at the polar positions. The patch sizes are different from each other, and the attractive interaction acts only between the same types of patches. The particles translate on a flat plane and rotate three-dimensionally. When varying the two patch sizes, the pressure, and interaction energy, various structures are observed. When the difference between two patch sizes is small, kagome lattices, hexagonal structures, and two-dimensional dodecagonal quasi-crystal structures are observed. When the difference between two patch sizes is large, chain-like structures are created. With lower temperature, sparse structures such as ring-like structures form.

Effect of the Interaction Length on Clusters Formed by Spherical One-Patch Particles on Flat Planes.

Considering that one-patch particles rotate three-dimensionally and translate on a two-dimensional flat plane, I performed isothermal-isochoric Monte Carlo simulations to study how two-dimensional self-assemblies formed by spherical patchy particles depending on the interaction length and patch area. As the interaction potential between one-patch particles, the Kern-Frenkel (KF) potential is used in the simulations. With increasing patch area, the shape of the most numerous clusters changes from dimers to island-like clusters with a square lattice via triangular trimers, square tetramers, and chain-like clusters when the interaction length is as long as the particle radius. With a longer interaction length, other shapes of polygonal clusters such as another type of square tetramers, two types of pentagonal pentamers, hexagonal hexamers, and hexagonal heptamers also form.

Changes in the blood flow of the femoral artery by botulinum toxin A in rats.

We examined the changes in blood flow in the femoral artery caused by botulinum toxin A in rats. Blood flow was measured using laser Doppler flowmetry. We used male Sprague-Dawley-derived rats weighing between 350 and 400 g. The study was performed on 6 groups; each of them consisted of 30 rats (control and botulinum toxin A 0.5, 1, 2, 4, and 8 units). The laser Doppler flowmetry revealed that blood flow in the femoral artery increased by the third day in the groups injected with 1 or more units of botulinum toxin A. In the groups injected with 8 units of botulinum toxin A, we recognized an increase of blood flow from the second day. Our results suggest that botulinum toxin A is concerned in improving blood flow.

Formation of various structures caused by particle size difference in colloidal heteroepitaxy.

By performing isothermal-isochoric Monte Carlo simulations with depletion force, the author investigated the dependence of the epitxial layer structure on the differences in the particle size between the substrate in colloidal heteroepitaxy. By changing the size of epitaxial particles and performing simulations comprehensively, various structures including the structures observed in a experiment, such as a honeycomb, one created by hexagonal heptamers, and one consisting of both pentagonal tiles and triangular tiles, were created. When the ratio of particle sizes between the epitxial layer and substrate takes a specific value, two types of hexagonal structures were created. One is the hexagonal layer parallel to the substrate layer and the other layer is rotated by 60[Formula: see text] from the substrate layer. The former structure was created over a wide range of particle-size ratios, whereas the latter structure was created when the particle-size ratio was only around the specific ratio, and it seemed a metastable structure.

Structures Formed by Particles with Shoulderlike Repulsive Interaction in Thin Systems.

When particles are constructed in thin systems between two parallel flat walls, structures that are not observed in bulk systems are created and the created structures change, depending on the width between the walls. In this study, the structures formed by particles constructed in thin systems were investigated through performing isothermal-isobaric Monte Carlo simulations, where the interaction between the particles is given by the hard-core square shoulder potential. By controlling the width of the shoulder-like repulsive interaction and the system width, several novel structures such as the connection of rhombuses and the square lattice of the (100) face of the body-centered cubic lattice were created.

Two-dimensional binary colloidal crystals formed by particles with two different sizes.

The formation of [Formula: see text] type two-dimensional binary colloidal crystals was studied by performing Monte Carlo simulations with two different size particles. The effect of interactions between particles and between particles and a wall, and the particles size ratios on the formation of [Formula: see text] structure were examined. [Formula: see text] structures formed efficiently when the interaction between equivalently sized particles was smaller than that between differently sized particles. To create [Formula: see text] on a wall, it was necessary to choose a suitable particles size ratios, and the attraction between the particles and the wall was greater than that between particles.

Clusters formed by dumbbell-like one-patch particles confined in thin systems.

Performing isothermal-isochoric Monte Carlo simulations, I examine the types of clusters that dumbbell-like one-patch particles form in thin space between two parallel walls, assuming that each particle is synthesized through the merging of two particles, one non-attracting and the other attracting for which, for example, the inter-particle interaction is approximated by the DLVO model . The shape of these dumbbell-like particles is controlled by the ratio of the diameters q of the two spherical particles and by the dimensionless distance l between these centers. Using a modified Kern-Frenkel potential, I examine the dependence of the cluster shape on l and q. Large island-like clusters are created when [Formula: see text]. With increasing q, the clusters become chain-like . When q increases further, elongated clusters and regular polygonal clusters are created. In the simulations, the cluster shape becomes three-dimensional with increasing l because the thickness of the thin system increases proportionally to l.

Synthesis of silica-coated AgI nanoparticles and immobilization of proteins on them.

This paper describes a method for preparing silica-coated silver iodide (AgI/SiO2) particles and immobilizing proteins on the AgI/SiO2 particles. Colloid solution of AgI particles was prepared by mixing AgClO4 aqueous solution and KI aqueous solution. Silica-coating of the AgI particles was performed by adding 3-mercaptopropyltrimethoxysilane, tetraethylorthosilicate/ethanol solution and NaOH aqueous solution successively to the AgI colloid solution. TEM observation revealed that the AgI nanoparticles were coated with uniform silica shell. The AgI/SiO2 particles were surface-modified with 3-aminopropyltrimethoxysilane and succinic anhydride. It was confirmed by XPS measurement that amino group or carboxyl group was introduced onto the AgI/SiO2 particles. Protein-immobilization was performed in aqueous solution with bovine serum albumin (BSA) in the presence of the surface-modified AgI/SiO2 particles. UV-VIS absorption spectroscopy revealed that the BSA was adsorbed on the surface-modified particles.

Effect of Patch Area and Interaction Length on Clusters and Structures Formed by One-Patch Particles in Thin Systems.

Assuming that the interaction between particles is given by the Kern-Frenkel potential, Monte Carlo simulations are performed to study the clusters and structures formed by one-patch particles in a thin space between two parallel walls. In isothermal-isochoric systems with a short interaction length, tetrahedral tetramers, octahedral hexamers, and pentagonal dipyramidal heptamers are created with increasing patch area. In isothermal-isobaric systems, the double layers of a triangular lattice, which is the (111) face of the face-centered cubic (fcc) lattice, form when the pressure is high. For a long interaction length, a different type of cluster, trigonal prismatic hexamers, is created. The structures in the double layers also changed as follows: a simple hexagonal lattice or square lattice, which is the (100) face of the fcc structure, is created in isothermal-isobaric systems.

Facile preparation of aminosilane-alginate hybrid beads for enzyme immobilization: Kinetics and equilibrium studies.

A simple, facile and potential platform for enzyme immobilization using alginate-based beads has been demonstrated by simultaneous gelation and modification of alginate using calcium chloride (CaCl2) and 3-aminopropyltriethoxysilane (APTES). In this method, sodium alginate solution containing enzyme was simply dripped into a crosslinker solution containing CaCl2 and APTES, leading to the formation of APTES-alginate hybrid beads (AP-beads). The optical observation, FT-IR analysis and amino group measurements provided evidence that APTES was successfully adsorbed to the alginate chain via electrostatic interaction. On the assumption that the binding of Ca2+ ion to polymannuronate residues of alginate via bidentate bridging coordination is competitive with APTES, the equilibrium isotherm and kinetics for the adsorption of APTES to AP-beads was found to follow extended Langmuir isotherm in binary system. Formate dehydrogenase (FDH) as a model enzyme was successfully immobilized in AP-beads and the immobilization yield of ca. 100% could be achieved under optimal conditions of CaCl2 and APTES concentrations in crosslinker solution. Furthermore, the AP-beads were reused efficiently for 9 cycles without loss of FDH activity. The above results demonstrated that AP-beads were effective support for enzyme immobilization.

Step wandering on Si(111) vicinal face near the 1 x 1<-->7 x 7 transition temperature with drift of adatoms parallel to steps.

On a Si(111) surface, which is covered with the 1 x 1 structure at high temperature, the 7 x 7 structure appears when temperature is lower than the structural transition temperature (860 degrees C) . On the vicinal face, the 7 x 7 structure spreads from the upper side of the step edge. The diffusion coefficient on the 1 x 1 structure is larger than that on the 7 x 7 structure. During growth, due to the difference in the diffusion coefficient, step wandering occurs and grooves perpendicular to the steps are formed. When the direct electric current is added parallel to the step, the grooves are tilted. In this paper, with taking account of the drift of adatoms caused by the direct current, we study the possibility of tilting of the grooves.

Effect of evaporation on step bunching induced by impurities.

In this paper, we study the effect of the evaporation of adatoms and impurities on the step bunching induced by impurity. Keeping the ratio of the impingement rate of impurities F_{imp} to that of atoms F constant, we carry out Monte Carlo simulation. In the system with the evaporation of impurities, the growth rate of vicinal face R is proportional to F. This relation is the same as that without the evaporation of impurities. When F is small, the vicinal face is unstable. Compared with the system without the evaporation of impurities, the effect of impurities is weakened. In our simulation, step pairing occurs but large bunches are not formed. When we take account of the evaporation of both impurities and adatoms, the vicinal face grows when F is larger than the equilibrium value F_{eq}. R is not proportional to (F-F_{eq}) and large bunches are formed when F is small. In this paper, we also show how the impurity density on surface σ_{imp} and that incorporated in solid ρ_{imp} are related to the formation of step bunches.

Two mechanisms forming a comblike step pattern induced by a moving linear adatom source.

We carry out phase field simulations to study properties of the comblike step patterns induced by an adatom source. When an adatom source advances right in front of a step, step wandering is caused by the asymmetry of the surface diffusion field and small protrusions are formed. If the velocity of the source V_{p} is smaller than a critical value V_{p}^{c}, the protrusions follow the adatom source with coarsening of the step pattern, and a regular comblike pattern with finger-like protrusions is formed. With a sufficiently small V_{p}, the gap of the supersaturation is large at the adatom source. Since the period of protrusions, Λ, decreases with increasing V_{p}, the coarsening of step pattern is irrelevant for the protrusions to catch up with the adatom source. Near V_{p}^{c}, the gap of the supersaturation at the adatom source is small. Taking account of the increase in Λ with increasing V_{p}, the coarsening of the step pattern is essential for the protrusions to follow the adatom source.

Period of a comblike pattern controlled by atom supply and noise.

Pattern formation of a step on a growing crystal surface induced by a straight line source of atoms, which is escaping from the step at a velocity V(p), is studied with the use of a phase field model. From a straight step, fluctuations of the most unstable wavelength λ(max) grow. Competition of intrusions leads to coarsening of the pattern, and survived intrusions grow exponentially. With sufficient strength of the crystal anisotropy, a regular comblike pattern appears. This peculiar step pattern is similar to that observed on a Ga-deposited Si(111) surface. The final period of the intrusions, Λ, is determined when the exponential growth ends. The period depends on the strength F(u) of a current noise in diffusion as Λ∼λ(max)|lnF(u)|: such a logarithmic dependence is confirmed for the first time. A nonmonotonic V(p) dependence of Λ indicates that the comblike pattern with a small V(p) is related to an unstable growth mode of the free needle growth in a channel. The pattern is stabilized by the guiding linear source.

Analysis of an inactivated Lg-FLO1 gene present in bottom-fermenting yeast.

During the course of investigating a flocculation-related gene of a bottom-fermenting yeast, we identified a new Lg-FLO1 homologue which contains the N-terminal domain of the Lg-FLO1 gene. The results of the partial DNA sequence analysis of the amplified product obtained by inverse-PCR suggested that the homologue contains a sequence present in the YIL169c (chr. IX of Saccharomyces cerevisiae). Southern blot analyses using the VTH1, HXT12, SDL1 and UBP7 genes as probes for chr. IX strongly indicated that an approximately 20-kb region from the YIL169c ORF to the left telomere in chr. IX translocated to the Lg-FLO1 ORF region in chr. VIII of bottom-fermenting yeast. This translocation might convert a flocculent cell to a non-flocculent one.

Breeding of brewer's yeast by hybridization between a top-fermenting yeast Saccharomyces cerevisiae and a cryophilic yeast Saccharomyces bayanus.

To improve the fermentability of a top-fermenting yeast at low-temperature, we performed hybridization trials between four top-fermenting Saccharomyces cerevisiae strains and a cryophilic yeast Saccharomyces bayanus YM84 with good fermentability at low-temperature. The hybrids selected using 5-bromo-4-chloro-3-indolyl-alpha-D-galactopyranoside were checked with pulsed-field gel electrophoresis and their brewing performance at the low-temperature of 10.5 degrees C was observed using small-scale (2 l) fermentation trials.

Effect of container shape and walls on solidification of Brownian particles in a narrow system.

We carry out Brownian dynamics simulations and study the ordering of particles under a uniform external force in a narrow system. In our previous studies [M. Sato et al., Phys. Rev. E 87, 032403 (2013); J. Phys. Soc. Jpn. 82, 084804 (2013)], we showed that the ordering of particles depends on the direction of the external force. In the studies, however, the system size and the number of particles are small, so the behaviors we observed corresponds to the motions in the initial stage of crystallization. In this paper, using a longer container and more particles, we investigate how solidification in a narrow system proceeds. We also study the effect of the shape of simulation box on the ordering of particles. When we use a rhomboid as a simulation box, the ratio of the particles with the face-centered cubic structure to those with the hexagonal close-packed structure is larger than that in a cuboid system.

Crystallization of Brownian particles in thin systems constrained by walls.

Keeping formation of a colloidal crystal by a centrifugal force in mind, we carry out Brownian dynamics simulations in thin systems and study ordering of particles induced by an external force. During solidification, the two-dimensional ordering along walls initially occurs. Then, the ordered particles on the walls act as substrates, and crystallization proceeds into bulk. When the external force is weak, the close-packed face of the crystal structure is parallel to the bottom wall. The direction of the close-packed face depends on the strength of the external force: The close-packed face becomes parallel to the side walls with a strong external force.

Surgical treatment of facial fracture by using unsintered hydroxyapatite particles/poly l-lactide composite device (OSTEOTRANS MX(®)): a clinical study on 17 cases.

BACKGROUND: In Japan we currently use absorption properties for facial fractures. OSTEOTRANS MX(®) (Takiron co., ltd, Japan) is an absorption device, which is called Super FIXSORB MX(®) in Japan. This absorbable osteosynthetic device constitutes unsintered hydroxyapatite particles/poly l-lactide (u-HA/PLLA) composites. This study focuses on reporting clinical cases of using OSTEOTRANS MX(®). MATERIALS AND METHODS: Seventeen patients (16 men and 1 woman) aged 10-80 years (mean: 39.9 years, SD: ±20.7) with 86 fracture sites were treated. In all cases we used 1.0 mm plates and 5 mm or 7 mm screws. The postoperative observation period was 6-60 months (mean: 21.8 months, SD: ±14.5). RESULTS: The fracture site recovered in all cases. Complications included one bone excess on the forehead and one foreign-body reaction on the frontozygomatic suture, but the fracture sites were recovered and had no problems. In the case with the longest observation time 60 months, the plate was almost fully absorbed. However, in other cases the plate was not fully absorbed because of a shorter observation time. CONCLUSION: OSTEOTRANS MX(®) is a useful device because of its suitable intensity, thinness, radiopaque, and few complications. A longer observation time is required for a plate to be absorbed completely.