Kyushu University Academic Staff Educational and Research Activities Database
List of Papers
Yoshiki Hidaka Last modified date:2021.05.28

Assistant Professor / Applied Physics / Department of Applied Quantum Physics and Nuclear Engineering / Faculty of Engineering

1. Noriko Oikawa, Tomohiro Gunji, and Yoshiki Hidaka, Grid pattern emerging from complex dynamics of defects, Physical Review E, 10.1103/PhysRevE.101.062204, 101, 062204-1-062204-7, 2020.06, The formation process and growth dynamics of the grid pattern, a cellular convective pattern in the electroconvection of nematic liquid crystals, are investigated. The grid pattern appears via a disordered state called defect turbulence with the increasing of an applied voltage. The averaged defect density increases with the applied voltage and then the defects that have been in the continuous process of creation and annihilation are frozen as grid cells forming domain structures. The area fraction of the grid domains is adopted as the order parameter. The temporal growth of the area fraction for the step voltage was also measured. By applying the Kolmogorov-Avrami model to the results, it is suggested that the growth dynamics of the grid domain is not primarily governed by domain growth, but by the local transition of the rolls to the cellular flow via preliminary grid structures that transiently appear..
2. Takayuki Narumi, Yoshiki Hidaka, Slow diffusive structure in Nikolaevskii turbulence, Physical Review E, 10.1103/PhysRevE.101.022202, 101, 2, 022202-1-022202-7, 2020.02, Weak turbulence has been investigated in nonlinear-nonequilibrium physics to understand universal characteristics near the transition point of ordered and disordered states. Here the one-dimensional Nikolaevskii turbulence, which is a mathematical model of weak turbulence, is studied theoretically. We calculate the velocity field of the Nikolaevskii turbulence assuming a convective structure and carry out tagged-particle simulations in the flow to clarify the Nikolaevskii turbulence from the Lagrangian description. The tagged particle diffuses in the disturbed flow and the diffusion is superdiffusive in an intermediate timescale between ballistic and normal-diffusive scale. The diffusion of the slow structure is characterized by the power law for the control parameter near the transition point of the Nikolaevskii turbulence, suggesting that the diffusive characteristics of the slow structure remain scale invariant. We propose a simplified model, named two-scale Brownian motion, which reveals a hierarchy in the Nikolaevskii turbulence..
3. Nguyen Sura, Hirotaka Okabe, Brian A. Omondi, Albert Mufundirwa, Yoshiki Hidaka, Kazuhiro Hara, Study on the influence of inductive groups on the performance of carboxylate-based hydrogel polymer network, Polymer Testing, 10.1016/j.polymertesting.2019.106117, 80, 2019.12, We report study on the effect of Br and CH3 inductive groups on the loading capacity of carboxylate-based hydrogel adsorbent. Synthesized sodium acrylate (NaAc) and 2-Bromoacrylic acid (BrAc) copolymer hydrogels for metal ion capture were characterized using FTIR, UV–Vis, 13C NMR, and DSC methods for structural and functional properties. Both FTIR and UV–Vis spectra indicated formation of a charge transfer complex between Br, CH3 groups and the carbonyl (C═O) group whereas solid-state NMR evidenced Br group appearance as an appendage on hydrogel backbone. By incorporating Br group on the hydrogel matrix and consequently exploiting the high electronegativity potential and inductive effect chemistry of this group, there was a significant increase in dissociation of H+ ions and hence higher loading capacity of carboxylate group. This facilitated higher ion exchange ability, resulting in up to 4 times increase in adsorption capacity during adsorption from multi-element metal ion competitive solution. Separately, when applied on single ion non-competitive solution, its adsorption capacity on vanadium increased three-fold from 119 mg/g to 373 mg/g due to the effect of Br group. However, the CH3 had a negating effect instead lowering the adsorption capacity (below 119 mg/g); while also caused lower swelling ratio of carboxylate-functionalized hydrogel adsorbents..
4. Tran Thu Hong, Hirotaka Okabe, Yoshiki Hidaka, Brian A. Omoldi, Kazuhiro Hara, Radiation induced modified CMC-based hydrogel with enhanced reusability for heavy metal ions adsorption, polymer, 10.1016/j.polymer.2019.121772, 181, 2019.10, The study attempted solving hazardous heavy-metal problems by creating a new eco-friendly functional hydrogel adsorbent (CSB-hydrogel). By utilizing γ-irradiation induced grafting and co-polymerization, the CSB-hydrogels were synthesized from a main bio-polymer {Sodium Carboxymethyl Cellulose (CMC)} and two active vinyl monomers {Sodium Styrene Sulfonate (SSS) and Bis[2-(Methacryloyloxy)Ethyl] Phosphate (BMEP)}. As well as the compression moduli, the CSB-hydrogels showed significant difference in the swelling capacities with the variety of BMEP-amounts. The author then examined the CSB-hydrogels’ multi-metal-ion adsorption capacities by performing the ion-capturing experiments with a varying species mixture solution and by utilizing ICP-MS analysis technique. The CSB-hydrogels demonstrated their highly-efficient recovery functionalities for most of the metal ions in the solution; especially, higher than 70% for nickel. Moreover, the CSB-hydrogels showed sufficient performance after 4-time repetitive adsorption-desorption treatments. With the high heavy-metal capturing-efficiency and the re-usability, the CSB-hydrogels were revealed to have a high potential as a new eco-friendly environment-purifying material..
5. K. Nagaoka, S. Hotta, Yoshiki Hidaka, T. Kobayashi, Kenichiro Terasaka, S. Yoshimura, Characteristics of electroconvection turbulence and proposal of its application to turbulent transport experiment in a rotating spherical shell, High Energy Density Physics, 10.1016/j.hedp.2019.03.006, 31, 79-82, 2019.04, An electroconvection (EC) in liquid crystal is used in the experimental study of turbulent transport. The transport characteristics in EC turbulence were investigated with a planer cell, and the diffusive property of turbulent transport was identified, which is identical to that of normal viscus fluid described by Navier–Stokes equation. Experimental research on turbulent transport using EC in a rotating spherical shell is proposed. A demonstration of the production of EC turbulence in a rotating spherical shell was carried out, where the radial gravity was replaced by electric field..
6. Thu Hong Tran, Hirotaka Okabe, Yoshiki Hidaka, Kazuhiro Hara, Equilibrium and kinetic studies for silver removal from aqueous solution by hybrid hydrogels, Journal of Hazardous Materials, 10.1016/j.jhazmat.2018.11.008, 365, 237-244, 2019.03, Hybrid hydrogels were prepared by blending Carboxymethyl chitosan (CMCts), Carboxymethyl cellulose (CMC) with Sodium sulfonate styrene (SSS) by 60-kGy gamma rays. The prepared hydrogels were utilized as silver-ion (Ag) sorbent under non- and competitive cases. Batch adsorption experiments were conducted in functional conditions including contact time, ratios of (CMC:CMCts) and SSS, pH value, temperature and adsorbent weight. Equilibrium contact time of 10 h. was obtained by the adsorption material. The optimal 4:2 ratio of (CMC:CMCts):SSS showed the Ag highest adsorption efficiency. The maximum percentage of Ag+ removal was achieved at the pH 5. The temperature effect on the adsorption ability of hybrid hydrogel indicated the Ag adsorption process was endothermic and spontaneous. The Langmuir isotherm model fitted Ag adsorption data well, assuming a monolayer adsorption with predicted maximum adsorption capacity of 451.74 × 10−3 mg. g–1. From the kinetic data, the process of Ag adsorption had higher agreement with the pseudo-2nd order model, predicting the amount of Ag+ uptake at different contact time intervals and at equilibrium..
7. Md Murshed Bhuyan, Omondi Brian Adala, Hirotaka Okabe, Yoshiki Hidaka, Kazuhiro Hara, Selective adsorption of trivalent metal ions from multielement solution by using gamma radiation-induced pectin-acrylamide-(2-Acrylamido-2-methyl-1-propanesulfonic acid) hydrogel, Journal of Environmental Chemical Engineering, 10.1016/j.jece.2018.102844, 7, 1, 2019.02, The present research is focused on the selective adsorption of trivalent metal ions from multielement solution by using functional hydrogel. The hydrogels were synthesized from the aqueous blend of Pectin, Acrylamide (AAm) and 2-Acrylamido-2-methyl-1-propanesulfonic acid (AMPS) by applying gamma radiation. The results of gel fraction and equilibrium swelling optimized 1:2:3 ratio of raw materials (pectin, AAm, and AMPS) and 2 kGy radiation dose for the preparation of hydrogels. The functional groups of the hydrogel were confirmed by Fourier transform infrared (FTIR) spectroscopy. The thermal properties were studied by differential scanning calorimetry (DSC) and scanning electron microscopy (SEM) equipped with energy dispersive X-ray spectroscopy (EDS) was used to analyze the surface morphology of hydrogels before and after metal adsorption. Hydrogels were applied to selective adsorption of five elements (Al, Cr, Fe, Ga, and In) from the multielement solution as well as adsorption from the manually prepared solution of five elements. The effect of pH on the adsorption capacity of hydrogel was examined. The adsorption data was used to study the adsorption isotherm models where the Freundlich adsorption isotherm model was found to be well fitted compared to the Langmuir adsorption isotherm model. From the Freundlich isotherm model, the maximum adsorption capacities of Al, Cr, Fe, Ga and In were found to be 11.34, 11.52, 11.92, 11.57 and 17.73 mg/g of gel respectively. Desorption efficiency was found to be about 80%. The research results suggest that the hydrogel can effectively be used for the recovery of above mentioned trivalent metal ions..
8. Kazuma Yamanaka, Takayuki Narumi, Megumi Hashiguchi, Hirotaka Okabe, Kazuhiro Hara, Yoshiki Hidaka, Time-dependent diffusion coefficients for chaotic advection due to fluctuations of convective rolls, Fluids, 10.3390/fluids3040099, 3, 4, 2018.12, The properties of chaotic advection arising from defect turbulence, that is, weak turbulence in the electroconvection of nematic liquid crystals, were experimentally investigated. Defect turbulence is a phenomenon in which fluctuations of convective rolls arise and are globally disturbed while maintaining convective rolls locally. The time-dependent diffusion coefficient, as measured from the motion of a tagged particle driven by the turbulence, was used to clarify the dependence of the type of diffusion on coarse-graining time. The results showed that, as coarse-graining time increases, the type of diffusion changes from superdiffusion ? subdiffusion ? normal diffusion. The change in diffusive properties over the observed timescale reflects the coexistence of local order and global disorder in the defect turbulence..
9. Tran Thu Hong, Hirotaka Okabe, Yoshiki Hidaka, Kazuhiro Hara, Radiation synthesis and characterization of super-absorbing hydrogel from natural polymers and vinyl monomer, Environmental Pollution, 10.1016/j.envpol.2018.07.129, 242, 1458-1466, 2018.11, This article exploits a new approach for synthesis of polysaccharide-based grafted sodium styrene sulfonate (SSS) super absorbent hydrogels (SAHs) in aqueous solution by γ-radiation under ambient conditions. Important optimal conditions for preparation of hydrogels with the best swelling ratio, such as gamma irradiation dose and the ratio of feed composition have been discussed. Characterization techniques such as the SEM/EDS, FTIR and DSC were used in describing the newly prepared hydrogels. The FTIR gave characteristic peaks for -SO
Na group at 1042 and 988 cm
, showing successful grafting of SSS onto the polysaccharide base material. The dependence of swelling behaviors in various pH solutions and salts solutions were investigated in detail. The prepared hybrid hydrogel showed most optimum swelling capacity at neutral pH whereas equilibrium swelling of SAHs was achieved within 5 h. The swelling of SAHs influenced obviously to metal ion removal percentage in solution..
10. Brian A. Omondi, Hirotaka Okabe, Yoshiki Hidaka, Kazuhiro Hara, Fabrication of poly (1, 4-dioxa-7, 12-diazacyclotetradecane-8, 11-dione) macrocyclic functionalized hydrogel for high selective adsorption of Cr, Cu and Ni, Reactive and Functional Polymers, 10.1016/j.reactfunctpolym.2018.06.006, 130, 90-97, 2018.09, Synthesis of hydrogel adsorbent for high selectivity and strong chelate removal of transition metals Cr, Cu and Ni was accomplished via sol-gel method using ligand monomers maleic acid and (2, 2′ ethylenedioxy) bis (ethylamine) reagent. We obtained a 14-membered macrocyclic functional unit called poly (1, 4-dioxa-7, 12-diazacyclotetradecane-8, 11-dione) as the main active sites for metal adsorption. The new adsorbent's cross-linked polymer chains was clearly visualized using SEM spectroscopy; whereas the FTIR, 13C NMR and EDX techniques demonstrated its structural and functional groups. With an improved chelating power, this macrocyclic hydrogel was able to ignore non-target substrates, instead showing high specificity for only Cu, Cr and Ni from both single and multi-ion competitive aqueous solutions, in the order Cr > Cu > Ni. Pseudo-second order kinetic model aptly described the adsorption process, revealing chemisorption as the main mechanism which proceeded based on the host-guest chelation principle of metal ions onto the gel's macrocyclic active sites. Thus a high performance, high selectivity adsorbent system was achieved using active sites bearing substrate recognition and isolation properties..
11. Brian A. Omondi, Hirotaka Okabe, Yoshiki Hidaka, Kazuhiro Hara, Synthesis and characterization of poly(1,4,7-trioxacycloundecane-8,11-dione) macrocyclic functionalized hydrogel for high selectivity adsorption and complexation of bismuth ion, Polymers, 10.3390/polym10060662, 10, 6, 2018.06, Macrocyclic functional hydrogels incorporating new poly cyclic active sites (1,4,7-trioxacycloundecane-8,11-dione) within their entire network, have been synthesized. Using the high-dilution coupling of the bi-functional monomers maleic acid and bis(chloroethyl)ether in a sol-gel chemistry synthesis, 11-membered chelate rings infused with three oxygen donor atoms were created and characterized, and their structures confirmed using Fourier transform infrared (FTIR) and nuclear magnetic resonance (NMR) spectroscopic analyses. The macrocyclic gel, designed for selective host-guest adsorption and complexation of metal substrates, was initially tested against an aqueous set of 14 metal competitive solutions, where it demonstrated exclusive selectivity for Bi3+ aq, with the other metals exhibiting zero adsorption. Further analysis using binary and single ion Bi3+-containing solutions showed a near-complete removal of Bi3+ using this polycyclic hydrogel, with 98% extraction efficiency and q = 9.80 mg/g. These results clearly confirm that the 1,4,7-trioxacycloundecane-8,11-dione cyclic sites are most suitable for high selectivity and capture of Bi. The metal substrates were entrapped within the 1,4,7-trioxacycloundecane-8,11-dione cyclic sites. Evidently, by exploiting the host-guest complexation chemistry of macrocycles, we were able to design hydrogel adsorbents whose networks were comprised entirely of macrocyclic active groups for possible purification works of copper involving bismuth impurities, and/or for efficient selective uptake and recovery of bismuth trace ions existing in highly competitive environments such as sea water..
12. Brian A. Omondi, Hirotaka Okabe, Yoshiki Hidaka, Kazuhiro Hara, Poly (1, 4-diazocane-5, 8-dione) macrocyclic-functionalized hydrogel for high selectivity transition metal ion adsorption, Reactive and Functional Polymers, 10.1016/j.reactfunctpolym.2018.02.003, 125, 11-19, 2018.04, We present a method of synthesizing macrocyclic hydrogel systems using sol-gel polymerization and for high selectivity adsorption works. The hydrogel was fabricated using maleic acid and ethylene diamine ligand and characterized using FTIR, Raman, SEM/EDX, 13C NMR and SAXS techniques. It was revealed that 1, 4-diazocane-5, 8-dione were the principal active sites of this adsorbent. These macrocyclic sites provided defined zones which limited capture and chelation of transition metal ions such that from single ion solutions, only ion substrates of between 1.23 and 1.29 Å ionic size were mainly adsorbed; whereas in case of metal-metal competitive solutions, then only 1.29 Å sized substrates would be adsorbed. This adsorption specificity required that aqua metals of these sizes be of octahedral configurations for more optimum host-gest chelation with the gel active sites. Since Fe(aq) effectively met these criteria, the gel adsorbent displayed outstanding specificity for Fe(aq) adsorption from different levels of competitive environments. Present adsorbent showed that macrocyclic chelate sites can be infused directly into the hydrogel network without any grafting, and facilitates a shape-based, size-limited adsorption. This hydrogel is a promising candidate for applications in heavy metal pollution remediation, drug development and fuel cell catalysts, where high specificity adsorptions are desirable..
13. Md Murshed Bhuyan, Hirotaka Okabe, Yoshiki Hidaka, Nirmal Chandra Dafader, Nazia Rahman, Kazuhiro Hara, Synthesis of pectin-N, N-dimethyl acrylamide hydrogel by gamma radiation and application in drug delivery (in vitro), Journal of Macromolecular Science, Part A: Pure and Applied Chemistry, 10.1080/10601325.2018.1442177, 55, 4, 369-376, 2018.04, The objective of the work is to synthesize pectin-N, N-Dimethylacrylamide (DMAA) hydrogel by gamma radiation without using any initiators and cross-linking agents. Effect of radiation doses on gel fraction and equilibrium swelling as a function of pH were studied, and 5 kGy radiation dose was found to be the optimum dose for hydrogel synthesis. The grafting /crosslinking was investigated by Fourier transform infrared spectroscopy. Thermal properties and surface morphology were studied by differential scanning calorimetry and scanning electron microscopy. To study the drug release kinetics, 5-fluorouracil was loaded into the hydrogel and in vitro release was carried out in simulated gastric and intestinal fluid. The release profile of drug showed that more than 90% of the loaded drugs were released after 4 hours at both gastric fluid and intestinal fluid pH. Drug release data was fitted into zero order, Higuchi and Korsmeyer-Peppas kinetic models. Higuchi model was found to be the best fitted and release exponent ‘n’ value of Korsmeyer-Peppas model indicated the non-Fickian transport..
14. Md Murshed Bhuyan, Hirotaka Okabe, Yoshiki Hidaka, Kazuhiro Hara, Pectin-[(3-acrylamidopropyl) trimethylammonium chloride-co-acrylic acid] hydrogel prepared by gamma radiation and selectively silver (Ag) metal adsorption, Journal of Applied Polymer Science, 10.1002/app.45906, 135, 8, 2018.02, Pectin-[(3-acrylamidopropyl) trimethylammonium chloride-co-acrylic acid] hydrogel has been prepared from the aqueous blend solution of pectin, (3-acrylamidopropyl) trimethylammonium chloride (APTAC), and acrylic acid (AAc) by applying gamma radiation of different doses (1–25 kGy) from 60Co gamma source. The hydrogels were characterized by equilibrium swelling, Fourier transform infrared, differential scanning calorimetry, and scanning electron microscopy. The hydrogels were used in multielement adsorption and it was found that pectin-(APTAC-co-AAc) gel is highly selective toward silver (I) ion among 27 metal ions. The data obtained from equilibrium adsorption studies were fitted in Langmuir and Freundlich adsorption isotherm models and model parameters evaluated. The maximum adsorption capacity of pectin-(APTAC-co-AAc) gel was found to be 67.6413 mg/g of dry gel at sample volume of 25 mL. The kinetic data were tested using pseudo-first order and pseudo-second order kinetic models and different adsorption diffusion models such as film diffusion and intra-particle diffusivity model. Thiourea solution was used for desorption of adsorbed metal ions from the hydrogel..
15. Kazuya Maeda, Takayuki Narumi, Rinto Anugraha, Hirotaka Okabe, Kazuhiro Hara, Yoshiki Hidaka, Sub-Diffusion in Electroconvective Turbulence of Homeotropic Nematic Liquid Crystals, Journal of the Physical Society of Japan, 10.7566/JPSJ.87.014401, 87, 014401-1-014401-5, 2017.12, Diffusion resulting from turbulence corresponding to dynamic scattering mode 1 (DSM1) of electroconvection was studied in experiments on homeotropically aligned systems of nematic liquid crystals. In such systems, electroconvection displays peculiar nonlinear phenomena arising from the interaction between its convection and the nematic director yielding Nambu–Goldstone modes. From an analogy with Brownian motion, the motion of tagged particles driven by the turbulence was analyzed using the time-dependent coefficient of diffusion, defined as the mean-square displacement divided by time. The results indicate that sub-diffusion occurs in a certain time range, suggesting that turbulence causes particles to rebound. Detailed observations of turbulence structures revealed that rebounding is induced by characteristic linear structures of the nematic director caused by turbulence. This sub-diffusion arising from the interaction between the nematic director and turbulence is specific to nematic liquid crystals..
16. Thu Hong Tran, Hirotaka Okabe, Yoshiki Hidaka, Kazuhiro Hara, Removal of metal ions from aqueous solutions using carboxymethyl cellulose/sodium styrene sulfonate gels prepared by radiation grafting, Carbohydrate Polymers, 10.1016/j.carbpol.2016.09.049, 157, 335-343, 2017.02, Sodium Carboxymethyl Cellulose (CMC[sbnd]Na)/Sodium Styrene Sulfonate (SSS) hydrogels with grafted and crosslinked polymeric networks were prepared by γ-radiation at atmosphere condition. The obtained hydrogels were characterized by gel fraction, swelling ratio, TGA and FTIR spectroscopy. The results showed the ratio of CMC and SSS 1:0 gave the highest gel fraction, compared with other ratios. The swelling capacity increased by increasing SSS content due to the presence of [sbnd]SO3Na, [sbnd]OH groups in gel structure. The FTIR spectrum of CMC/SSS gel showed the new absorption peaks at 1034 and 1012 cm−1 corresponds to [sbnd]SO3Na group. The metal ion adsorption capacity of CMC/SSS gel was investigated. The grafted gel effectively removed metal ions, especially Cr and Pb. The effects of hydrogel composition, contact time, and initial concentration on the adsorption capacity of the grafted hydrogels were studied. The adsorption kinetics and equilibrium isotherms were investigated using pseudo-second-order model and Langmuir model..
17. Takayuki Narumi, Yosuke Mikami, Tomoyuki Nagaya, Hirotaka Okabe, Kazuhiro Hara, Yoshiki Hidaka, Relaxation with long-period oscillation in defect turbulence of planar nematic liquid crystals, Physical Review E, 10.1103/PhysRevE.94.042701, 94, 042701-1-042701-6, 2016.10, [URL], Through experiments, we studied defect turbulence, a type of spatiotemporal chaos in planar systems of nematic liquid crystals, to clarify the chaotic advection of weak turbulence. In planar systems of large aspect ratio, structural relaxation, which is characterized by the dynamic structure factor, exhibits a long-period oscillation that is described well by a combination of a simple exponential relaxation and underdamped oscillation. The simple relaxation arises as a result of the roll modulation while the damped oscillation is manifest in the repetitive gliding of defect pairs in a local area. Each relaxation is derived analytically by the projection operator method that separates turbulent transport into a macroscopic contribution and fluctuations. The analysis proposes that the two relaxations are not correlated. The nonthermal fluctuations of defect turbulence are consequently separated into two independent Markov processes. Our approach sheds light on diversity and universality from a unified viewpoint for weak turbulence..
18. Kazuhiro Hara, Seiya Fujiwara, Tetsumasa Fujii, Satoru Yoshioka, Yoshiki Hidaka, Hirotaka Okabe, Attempts to capturing ppb-level elements from sea water with hydrogels, Progress in Nuclear Energy, 10.1016/j.pnucene.2015.04.017, 92, 228-233, 2016.09, Stable energy resource supply is an important subject from the perspective of national security. In this sense, recovering uranium from seawater is important and profitable for the countries of which the land is surrounded by sea and is not endowed with energy resources such as Japan. However, the concentration of uranium dissolved in seawater is extremely low (ppb level) but the total amount of uranium is huge because of the tremendous seawater volume on the Earth. Therefore, in order to promote the efficiency of adsorbents capturing ppb-level uranium from seawater, the authors propose the utilization of hydrogel as a new adsorbent base material. In order to demonstrate the usefulness of the hydrogel for the ppb-level element-adsorption from seawater, the authors have developed the amidoxime incorporated hydrogel and have examined their ppb-level uranium capturing efficiency in the presence of other elements. From the experimental results, a potential for this purpose has been demonstrated by considerably high adsorption functionality..
19. Brian A. Omondi, Ronald Nguele, Hirotaka Okabe, Yoshiki Hidaka, Kazuhiro Hara, Multicomponent adsorption of benzene and selected borderline heavy metals by poly (butadiene-co-acrylic acid) hydrogel, Journal of Environmental Chemical Engineering, 10.1016/j.jece.2016.07.013, 4, 3, 3385-3392, 2016.09, This study introduces a method to alleviate against non-point source water pollution which typically comprises both organic and inorganic pollutants. We synthesized a hydrogel adsorbent customized for simultaneous adsorption (and removal) of benzene and heavy metals ion pollutants. Two functional groups were successfully incorporated into the hydrogel system using solution polymerization and chemical cross-linking methods. The adsorbent was golden brown and insoluble in water, and its structural decomposition in the dry state started at around 175°C. Other thermal properties, hydrogel characterization and adsorption mechanism are described herein. Exploiting the alkylating chemistry of mono-aromatic compounds, this hydrogel successfully adsorbed benzene onto its heterogeneous surface. The strong nature of adsorption with a relatively faster equilibrium time progressed according to second order kinetic model. However, competitive heavy metal ions adsorption was a diffusion-limited process and the adsorption capacity increased not only with the solution pH but also with ionic size and the amount of metal ions’ electric charge. With both type of pollutants adsorbed onto PBA hydrogel, this work therefore opens up a possibility of synthesizing adsorbent systems customized for simultaneous removal of organic and inorganic pollutants in a multi-type polluted waters..
20. Tomoyuki Nagaya, Yuki Satou, Yoshitomo Goto, Yoshiki Hidaka, Hiroshi Orihara, Viscosity of Liquid Crystal Mixtures in the Presence of Electroconvection, Journal of the Physical Society of Japan, 10.7566/JPSJ.85.074002, 85, 074002-1-074002-4, 2016.06, We have experimentally investigated the viscosity of nematic liquid crystal mixtures of p-methoxybenzylidene-p′-n-butylaniline (MBBA) and p-ethoxybenzylidene-p′-cyanoaniline (EBCA) in the presence of electroconvection under an ac electric field with 60 Hz. Although the viscosity of the mixtures with negative dielectric anisotropy shows a characteristic decrease in the high-voltage regime, that with positive dielectric anisotropy shows a monotonic increase as the applied voltage is increased. The experimental results suggest that the decrease in viscosity observed only for the mixtures with negative dielectric anisotropy is attributed to the negative contribution of electric stress caused by the anisotropic director distribution of the turbulent state..
21. Md Murshed Bhuyan, Nirmal Chandra Dafader, Kazuhiro Hara, Hirotaka Okabe, Yoshiki Hidaka, Md Mizanur Rahman, Mohammad Mizanur Rahman Khan, Nazia Rahman, Synthesis of Potato Starch-Acrylic-Acid Hydrogels by Gamma Radiation and Their Application in Dye Adsorption, International Journal of Polymer Science, 10.1155/2016/9867859, 2016, 2016, Several kinds of acrylic-acid-grafted-starch (starch/AAc) hydrogels were prepared at room temperature (27°C) by applying 5, 10, 15, 20, and 25 kGy of gamma radiation to 15% AAc aqueous solutions containing 5, 7.5, and 15% of starch. With increment of the radiation dose, gel fraction became higher and attained the maximum (96.5%) at 15 kGy, above which the fraction got lowered. On the other hand, the gel fraction monotonically increased with the starch content. Swelling ratios were lower for the starch/AAc hydrogels prepared with higher gamma-ray doses and so with larger starch contents. Significant promotions of the swelling ratios were demonstrated by hydrolysis with NaOH: 13632 ± 10 % for 15 kGy radiation-dosed [5% starch/15% AAc] hydrogel, while the maximum swelling ratio was 200% for those without the treatment. The authors further investigated the availability of the starch/AAc hydrogel as an adsorbent recovering dye waste from the industrial effluents by adopting methylene blue as a model material; the hydrogels showed high dye-capturing coefficients which increase with the starch ratio. The optimum dye adsorption was found to be 576 mg per g of the hydrogel having 7.5 starch and 15% AAc composition. Two kinetic models, (i) pseudo-first-order and (ii) pseudo-second-order kinetic models, were applied to test the experimental data. The latter provided the best correlation of the experimental data compared to the pseudo-first-order model..
22. Yoshiki Hidaka, Megumi Hashiguchi, Noriko Oikawa, Shoichi Kai, Lagrangian chaos and particle diffusion in electroconvection of planar nematic liquid crystals, Physical Review E, 10.1103/PhysRevE.92.032909, 92, 032909-1-032909-6, 2015.09, Two types of spatiotemporal chaos in the electroconvection of nematic liquid crystals, such as defect turbulence and spatiotemporal intermittency, have been statistically investigated according to the Lagrangian picture. Here fluctuations are traced using the motion of a single particle driven by chaotic convection. In the defect turbulence (fluctuating normal rolls), a particle is mainly trapped in a roll but sometimes jumps to a neighboring roll. Its activation energy is then obtained from the jumping (hopping) rate. This research clarifies that diffusion in the defect turbulence regime in electroconvection can be regarded as a kind of hopping process. The spatiotemporal intermittency appears as a coexistent state of ordered grid domains and turbulent domains. The motion of a single particle shows weak and strong diffusion, respectively, in the ordered and turbulent domains. The diffusion characteristics intermittently change from one to another with certain durations as the domains change. This research has found that the distribution function of the duration that a particle remains in an ordered area has a power-law decay for which the index is different from that obtained by the Eulerian measurement..
23. Misato Iino, Yoshiki Hidaka, Fahrudin Nugroho, Rinto Anugraha, Hirotaka Okabe, Kazuhiro Hara, Responses of spatiotemporal chaos to oscillating forces, Physical Review E - Statistical, Nonlinear, and Soft Matter Physics, 10.1103/PhysRevE.92.012916, 92, 1, 2015.07, The responses of soft-mode turbulence, a kind of spatiotemporal chaos seen in electroconvection of a nematic liquid crystal, to alternating-current magnetic fields is investigated to uncover the dynamical properties of spatiotemporal chaos. The dynamical responses can be measured by an order parameter, Mp(t), which indicates ordering in the convective roll pattern induced by the magnetic field. Determined by properties of the liquid crystal in a magnetic field, Mp(t) oscillates in accordance with the square of the magnetic field. The relaxation time of the system was obtained by fitting the frequency dependence of the complex susceptibility for the pattern obtained from the oscillation of Mp(t) to the Debye-type relaxation spectra. However, for the high-frequency regime, the susceptibility deviates from the spectra because slow and large fluctuations of Mp(t) contribute to the oscillation. The properties of this type of fluctuation were investigated by introducing a dynamic ordering parameter defined as the period average of Mp(t)..
24. Yuji Sasaki, Yoshinori Takikawa, V. S.R. Jampani, Hikaru Hoshikawa, Takafumi Seto, Christian Bahr, Stephan Herminghaus, Yoshiki Hidaka, Hiroshi Orihara, Colloidal caterpillars for cargo transportation, Soft Matter, 10.1039/c4sm01354a, 10, 44, 8813-8820, 2014.11, Tunable transport of tiny objects in fluid systems is demanding in diverse fields of science such as drug delivery, active matter far from equilibrium, and lab-on-a-chip applications. Here, we report the directed motion of colloidal particles and self-assembled colloidal chains in a nematic liquid crystal matrix using electrohydrodynamic convection (EHC) rolls. The asymmetric distortion of the molecular orientation around the particles results-for single particles-in a hopping motion from one EHC roll to the next and-for colloidal chains-in a caterpillar-like motion in the direction perpendicular to the roll axes. We demonstrate the use of colloidal chains as microtraction engines for the transport of various types of microcargo. This journal is.
25. Katsuhiro Kobayashi, Hirotaka Okabe, Shinya Kawano, Yoshiki Hidaka, Kazuhiro Hara, Biophoton emission induced by heat shock, PloS one, 10.1371/journal.pone.0105700, 9, 8, 2014.08, Ultraweak biophoton emission originates from the generation of reactive oxygen species (ROS) that are produced in mitochondria as by-products of cellular respiration. In healthy cells, the concentration of ROS is minimized by a system of biological antioxidants. However, heat shock changes the equilibrium between oxidative stress and antioxidant activity, that is, a rapid rise in temperature induces biophoton emission from ROS. Although the rate and intensity of biophoton emission was observed to increase in response to elevated temperatures, pretreatment at lower high temperatures inhibited photon emission at higher temperatures. Biophoton measurements are useful for observing and evaluating heat shock..
26. Yoshiki Hidaka, Noriko Oikawa, Chaos and Spatiotemporal Chaos in Convective Systems, FORMA, 10.5047/forma.2014.005, 29, 1, 29-32, 2014.07, Much of early research on chaos from the viewpoint of physics was performed using spatially confined convective systems. In spatially extended convective systems, on the other hand, spatiotemporal chaos occurs. However, there is no unified definition for the term spatiotemporal chaos as for chaos. To unify definition, a property common to the three kinds of spatiotemporal chaos observed in electroconvection of nematic liquid crystals is presented..
27. Nazia Rahman, Nobuhiro Sato, Masaaki Sugiyama, Yoshiki Hidaka, Hirotaka Okabe, Kazuhiro Hara, Selective Hg(II) adsorption from aqueous solutions of Hg(II) and Pb(II) by hydrolyzed acrylamide-grafted PET films, Journal of Environmental Science and Health - Part A Toxic/Hazardous Substances and Environmental Engineering, 10.1080/10934529.2014.882209, 49, 7, 798-806, 2014.06, Selective Hg(II) adsorption from aqueous solutions of Hg(II) and Pb(II) using hydrolyzed acrylamide (AAm)-grafted polyethylene terephthalate (PET) films was examined to explore the potential reuse of waste PET materials. Selective recovery of Hg(II) from a mixture of soft acids with similar structure, such as Hg(II) and Pb(II), is important to allow the reuse of recovered Hg(II). An adsorbent for selective Hg(II) adsorption was prepared by γ-ray-induced grafting of AAm onto PET films followed by partial hydrolysis through KOH treatment. The adsorption capacity of the AAm-grafted PET films for Hg(II) ions increased from 15 to 70 mg/g after partial hydrolysis because of the reduction of hydrogen bonding between -CONH2 groups and the corresponding improved access of metal ions to the amide groups. The prepared adsorbent was characterized by Fourier transform infrared spectroscopy and scanning electron microscopy. The absorbent film showed high selectivity for the adsorption of Hg(II) over Pb(II) throughout the entire initial metal concentration range (100-500 mg/L) and pH range (2.2-5.6) studied. The high selectivity is attributed to the ability of Hg(II) ions to form covalent bonds with the amide groups. The calculated selectivity coefficient for the adsorbent binding Hg(II) over Pb(II) was 19.2 at pH 4.5 with an initial metal concentration of 100 mg/L. Selective Hg(II) adsorption equilibrium data followed the Langmuir model and kinetic data were well fitted by a pseudo-second-order equation. The adsorbed Hg(II) and Pb(II) ions were effectively desorbed from the adsorbent film by acid treatment, and the regenerated film showed no marked loss of adsorption capacity upon reuse for selective Hg(II) adsorption..
28. Nazia Rahman, Nobuhiro Sato, Masaaki Sugiyama, Yoshiki Hidaka, Hirotaka Okabe, Kazuhiro Hara, The effect of hot DMSO treatment on the γ-ray-induced grafting of acrylamide onto PET films, Polymer Journal, 10.1038/pj.2014.12, 46, 7, 412-421, 2014.01, In the present study, the γ-ray induced grafting of acrylamide (AAm) onto poly(ethylene terephthalate) (PET) films and the resulting changes in properties, including the Hg(II)-capturing functionality, were investigated. No grafting was observed on pristine PET films. Therefore, the films were treated with dimethyl sulfoxide (DMSO) before the γ-ray grafting with the goal of facilitating grafting; some of the samples were pretreated at high temperature (100-160 °C) and showed a considerable increase in the adsorption of AAm from solution. The highest graft yield obtained in the present study was 15.5% for the DMSO specimens pretreated at 140 °C and γ-ray irradiated with a 100-kGy total dose (1-kGy h-1 dose rate) in 50 wt% AAm-monomer solutions in the presence of 1 wt% FeCl 3 (polymerization inhibitor). In addition to the promotion of the graft yield, the formation of micropores in the DMSO-pretreated specimens was found during the optical microscopy investigations. This structural change is hypothesized to assist the adsorption and γ-ray grafting of AAm to PET. The AAm-grafted PET films prepared using DMSO pretreatment showed high removal efficiency for Hg(II) ions, whereas the pristine PET film showed no uptake, reflecting these changes..
29. Masaru Suzuki, Hiroshi Sueto, Yusaku Hosokawa, Naoyuki Muramoto, Takayuki Narumi, Yoshiki Hidaka, Shoichi Kai, Duality of diffusion dynamics in particle motion in soft-mode turbulence, Physical Review E - Statistical, Nonlinear, and Soft Matter Physics, 10.1103/PhysRevE.88.042147, 88, 4, 2013.10, Nonthermal Brownian motion is investigated experimentally by injecting a particle into soft-mode turbulence (SMT), in the electroconvection of a nematic liquid crystal. It is clarified that the particle motion can be classified into two phases: fast motion, where particles move with the local convective flow, and slow motion, where they are carried by global slow pattern dynamics. We propose a simplified model to clarify the mechanism of the short-time and asymptotic behavior of diffusion. In our model, the correlation time is estimated as a function of a control parameter E. The scaling of the SMT pattern correlation time, τd∼E-1, is estimated from the particle dynamics, which is consistent with a previous report observed from the Eulerian viewpoint. The origin of the non-Gaussian distribution of the displacement in the short-time regime is also discussed and an analytical curve is introduced that quantitatively agrees with the experimental data. Our results clearly illustrate the characteristics of diffusive motion in SMT, which are considerably different from the conventional Brownian motion..
30. Yusril Yusuf, Yoshiki Hidaka, Shoichi Kai, Dynamical behavior of prewavy pattern near nematic-isotropic transition, Journal of the Physical Society of Japan, 10.7566/JPSJ.82.044601, 82, 4, 2013.04, We report new results about a type of electrohydrodynamic instability, the prewavy instability, in a homeotropic nematic liquid crystal in a high-frequency electric field. This instability is seen in the form of a series of bright and dark stripes in between two crossed polarizers. The stripe formation corresponds to the periodic modulation of the rotation angle of the director in the xy-plane with periodicity along the x-direction. The dynamical behavior of prewavy patterns near the nematic-isotropic transition is reported. We found that the isotropic phase, due to the Joule heating effect, starts to grow in the dark stripes, i.e., in the vicinity of in-plane rotation angle α = 0..
31. T. Narumi, F. Nugroho, J. Yoshitani, Y. Hidaka, M. Suzuki, S. Kai, Compressed exponential relaxation as superposition of dual structure in pattern dynamics of nematic liquid crystals, 4th International Symposium on Slow Dynamics in Complex Systems: Keep Going Tohoku 4th International Symposium on Slow Dynamics in Complex Systems Keep Going Tohoku, 10.1063/1.4794604, 403-410, 2013.03, Soft-mode turbulence (SMT) is the spatiotemporal chaos observed in homeotropically aligned nematic liquid crystals, where non-thermal fluctuations are induced by nonlinear coupling between the Nambu-Goldstone and convective modes. The net and modal relaxations of the disorder pattern dynamics in SMT have been studied to construct the statistical physics of nonlinear nonequilibrium systems. The net relaxation dynamics is well-described by a compressed exponential function and the modal one satisfies a dual structure, dynamic crossover accompanied by a breaking of time-reversal invariance. Because the net relaxation is described by a weighted mean of the modal ones with respect to the wave number, the compressed-exponential behavior emerges as a superposition of the dual structure. Here, we present experimental results of the power spectra to discuss the compressed-exponential behavior and the dual structure from a viewpoint of the harmonic analysis. We also derive a relationship of the power spectra from the evolution equation of the modal autocorrelation function. The formula will be helpful to study non-thermal fluctuations in experiments such as the scattering methods..
32. Takayuki Narumi, Junichi Yoshitani, Masaru Suzuki, Yoshiki Hidaka, Fahrudin Nugroho, Tomoyuki Nagaya, Shoichi Kai, Memory function of turbulent fluctuations in soft-mode turbulence, Physical Review E - Statistical, Nonlinear, and Soft Matter Physics, 10.1103/PhysRevE.87.012505, 87, 1, 2013.01, Modal relaxation dynamics has been observed experimentally to clarify statistical-physical properties of soft-mode turbulence, the spatiotemporal chaos observed in homeotropically aligned nematic liquid crystals. We found a dual structure, dynamical crossover associated with violation of time-reversal invariance, the corresponding time scales satisfying a dynamical scaling law. To specify the origin of the dual structure, the memory function due to nonthermal fluctuations has been defined by a projection-operator method and obtained numerically using experimental results. The results of the memory function suggest that the nonthermal fluctuations can be divided into Markov and non-Markov contributions; the latter is called the turbulent fluctuation (TF). Consequently, the relaxation dynamics is separated into three characteristic stages: bare-friction, early, and late stages. If the dissipation due to TFs dominates over that of the Markov contribution, the bare-friction stage contracts; the early and late stages then configure the dual structure. The memory effect due to TFs results in a time-reversible relaxation at the early stage, and the disappearance of the memory by turbulent mixing leads to a simple exponential relaxation at the late stage. Furthermore, the memory effect due to TFs is shown to originate from characteristic spatial coherency called the patch structure..
33. Kohei Koyama, Yoshiki Hidaka, Masayuki Ushio, Dynamic Scaling in the Growth of a Non-Branching Plant, Cardiocrinum cordatum, PloS one, 10.1371/journal.pone.0045317, 7, 9, 2012.09, We investigated whole-plant leaf area in relation to ontogenetic variation in leaf-size for a forest perennial herb, Cardiocrinum cordatum. The 200-fold ontogenetic variability in C. cordatum leaf area followed a power-law dependence on total leaf number, a measure of developmental stage. When we normalized for plant size, the function describing the size of single leaves along the stem was similar among different-sized plants, implying that the different-sized canopies observed at different times in the growth trajectory were fundamentally similar to each other. We conclude that the growth trajectory of a population of C. cordatum plant leaves obeyed a dynamic scaling law, the first reported for a growth trajectory at the whole-plant level..
34. Fahrudin Nugroho, Takayuki Narumi, Yoshiki Hidaka, Junichi Yoshitani, Masaru Suzuki, Shoichi Kai, Glassy dynamics in relaxation of soft-mode turbulence, Physical Review E - Statistical, Nonlinear, and Soft Matter Physics, 10.1103/PhysRevE.85.030701, 85, 3, 2012.03, The autocorrelation function of pattern fluctuation is used to study soft-mode turbulence (SMT), a spatiotemporal chaos observed in homeotropic nematics. We show that relaxation near the electroconvection threshold deviates from the exponential. To describe this relaxation, we propose a compressed exponential appearing in dynamics of glass-forming liquids. Our findings suggest that coherent motion contributes to SMT dynamics. We also confirmed that characteristic time is inversely proportional to electroconvection's control parameter..
35. Fahrudin Nugroho, Yoshiki Hidaka, Tatsuhiro Ueki, Shoichi Kai, Transient mode selections in soft-mode turbulence by controlling the Nambu-Goldstone modes, journal of the physical society of japan, 10.1143/JPSJ.81.024004, 81, 2, 2012.02, We have studied the soft-mode turbulence (SMT), a type of spatiotemporal chaos observed in the electroconvection of the homeotropic nematic liquid crystals, induced by nonlinear interaction between the long-wave length Nambu-Goldstone modes and the short-wave length convective modes. By applying an external magnetic field H, the NG mode can be controlled and as a result an ordered pattern may be observed. Transiently it is achieved by the dynamical changes of the many domains consisting of regular rolls. Removing the magnetic field, then, the ordered state relaxes to its original SMT pattern. The transient dynamics of such a relaxation process is also investigated. An order parameter called as M p is used as a quantitative indicator for the transient process. We reveal two regimes of relaxation process: regime I and regime II correspond to the superposition of the modes and the free rotation of wavevector q(r) of the electroconvective pattern, respectively..
36. Takayuki Narumi, Masaru Suzuki, Yoshiki Hidaka, Tetsuya Asai, Shoichi Kai, Active Brownian motion in threshold distribution of a Coulomb blockade model, Physical Review E - Statistical, Nonlinear, and Soft Matter Physics, 10.1103/PhysRevE.84.051137, 84, 5, 2011.11, Randomly distributed offset charges affect the nonlinear current-voltage property via the fluctuation of the threshold voltage above which the current flows in an array of a Coulomb blockade (CB). We analytically derive the distribution of the threshold voltage for a model of one-dimensional locally coupled CB arrays and propose a general relationship between conductance and distribution. In addition, we show that the distribution for a long array is equivalent to the distribution of the number of upward steps for aligned objects of different heights. The distribution satisfies a novel Fokker-Planck equation corresponding to active Brownian motion. The feature of the distribution is clarified by comparing it with the Wigner and Ornstein-Uhlenbeck processes. It is not restricted to the CB model but is instructive in statistical physics generally..
37. Takayuki Narumi, Masaru Suzuki, Yoshiki Hidaka, Shoichi Kai, Size dependence of current-voltage properties in Coulomb blockade networks, journal of the physical society of japan, 10.1143/JPSJ.80.114704, 80, 11, 2011.11, We theoretically investigate the current-voltage (I-V) property of two-dimensional Coulomb blockade (CB) arrays by conducting Monte Carlo simulations. The I-V property can be divided into three regions and we report the dependence of the aspect ratio δ (namely, the lateral size N y over the longitudinal one Nx). We show that the average CB threshold obeys a power-law decay as a function of δ. Its exponent γ corresponds to a sensitivity of the threshold depending on δ, and is inversely proportional to Nx (i.e., δ at fixed N y). Further, the power-law exponent ζ, characterizing the nonlinearity of the I-V property in the intermediate region, logarithmically increases as δ increases. Our simulations describe the experimental result ζ = 2:25 obtained by Parthasarathy et al. [Phys. Rev. Lett. 87 (2001) 186807]. In addition, the asymptotic I-V property of one-dimensional arrays obtained by Bascones et al. [Phys. Rev. B 77 (2008) 245422] is applied to two-dimensional arrays. The asymptotic equation converges to the Ohm's law at the large voltage limit, and the combined tunneling-resistance is inversely proportional to δ. The extended asymptotic equation with the first-order perturbation well describes the experimental result obtained by Kurdak et al. [Phys. Rev. B 57 (1998) R6842]. Based on our asymptotic equation, we can estimate physical values that it is hard to obtain experimentally..
38. Annop Klamchuen, Takeshi Yanagida, Masaki Kanai, Kazuki Nagashima, Keisuke Oka, Sakon Rahong, Meng Gang, Mati Horprathum, Masaru Suzuki, Yoshiki Hidaka, Shoichi Kai, Tomoji Kawai, Study on transport pathway in oxide nanowire growth by using spacing-controlled regular array, Applied Physics Letters, 10.1063/1.3660246, 99, 19, 2011.11, Metal oxide nanowires formed via vapor-liquid-solid (VLS) process are promising nanoscale building blocks. Although understanding material transport pathways across three phases is crucial to realize well-defined oxide nanowires, such knowledge is unfortunately far from comprehensive. Here we investigate the material transport pathway in VLS grown MgO nanowires by utilizing spacing-controlled regular array. Defining the regular spacing of catalysts allows us to extract the information of transport pathway for each catalyst. We found the significant contribution of vapor phase transport pathway rather than the surface diffusion transport. This result highlights the critical role of re-evaporation process on VLS oxide nanowires..
39. Fahrudin Nugroho, Tatsuhiro Ueki, Rinto Anugraha, Yoshiki Hidaka, Shoichi Kai, Quantitative definition of patterns in soft-mode turbulence suppressing the Nambu-Goldstone mode, Physical Review E - Statistical, Nonlinear, and Soft Matter Physics, 10.1103/PhysRevE.84.011709, 84, 1, 2011.07, Chaotic patterns in electroconvection of homeotropic nematics, soft-mode turbulence (SMT), and the related spatiotemporal chaos (STC) are discussed, and the quantitative definition of the patterns is considered. The order parameter S, obtained directly from the 2D spectra of the patterns, is introduced. The contribution of the Nambu-Goldstone mode and the increase in pattern regularity under the influence of an external magnetic field H are evaluated. We propose a schematic phase diagram of STC patterns based on the value of S..
40. Masaru Suzuki, Yoshiki Hidaka, Takeshi Yanagida, Annop Klamchuen, Masaki Kanai, Tomoji Kawai, Shoichi Kai, Essential role of catalyst in vapor-liquid-solid growth of compounds, Physical Review E - Statistical, Nonlinear, and Soft Matter Physics, 10.1103/PhysRevE.83.061606, 83, 6, 2011.06, The mechanism of the solidification of compound materials, such as oxide crystals, in a vapor-liquid-solid (VLS) system is investigated by model molecular dynamics simulation. A simple model for the VLS growth of a compound crystal is proposed to clarify the general mechanism of how a liquid solvent catalyzes the growth rate. We find that the nucleation process at the solid surface is responsible for limiting the growth rate, and that the solvent catalyzes the nucleation by reducing the critical nucleation size at the liquid-solid interface. Our theoretical suggestion that the ratio of the vapor-solid (VS) growth rate to the VLS growth rate strongly depends on the supply rate qualitatively agrees well with the experimental result. Finally, we simulate the entire process of VLS nanowire formation..
41. Rinto Anugraha, Fahrudin Nugroho, Tatsuhiro Ueki, Yoshiki Hidaka, Shoichi Kai, Michael I. Tribelsky, Link of microscopic and macroscopic fields in nematodynamics, Physical Review E - Statistical, Nonlinear, and Soft Matter Physics, 10.1103/PhysRevE.83.022701, 83, 2, 2011.02, We have found an unusual and unexpected link between micro- (nematic director) and macro- (velocity) fields in nematodynamics, which exhibits itself in extended defects of a new type. In particular, we have shown that black lines (BLs) observed in electroconvection of a homeotropically aligned nematic layer are simultaneously Bloch's domain walls for the director field and lines of zero velocity intersecting a roll pattern for the convection. A detailed experimental study revealing the fine structure of BLs and their point defects is presented..
42. Annop Klamchuen, Takeshi Yanagida, Masaki Kanai, Kazuki Nagashima, Keisuke Oka, Shu Seki, Masaru Suzuki, Yoshiki Hidaka, Shoichi Kai, Tomoji Kawai, Dopant homogeneity and transport properties of impurity-doped oxide nanowires, Applied Physics Letters, 10.1063/1.3549703, 98, 5, 2011.01, Controlling and understanding an impurity doping on semiconductor oxide nanowires grown by the vapor-liquid-solid (VLS) method remains an important challenge. Homogeneous dopant distribution within oxide nanowires has been assumed without the direct evaluations to interpret the transport properties. Here we report the direct measurements of dopant distributions for Ta-doped SnO2 nanowires. We find that differences in dopant incorporations between VLS and vapor-solid growth processes give rise to a heavily doped shell surrounding an underdoped core. Thus, understanding the dopant incorporation pathways is essential to designing and controlling impurity doping on VLS grown oxide nanowires..
43. Fahrudin Nugroho, Tatsuhiro Ueki, Rinto Anugraha, Yoshiki Hidaka, Shoichi Kai, Magnetic field dependence of spatiotemporal chaos in a homeotropic nematic system, journal of the physical society of japan, 10.1143/JPSJ.79.123001, 79, 12, 2010.12, We investigate the response of electroconvective patterns to an external magnetic field H in a homeotropic nematic system where spatiotemporal chaos called soft-mode turbulence (SMT) occurs. The pattern ordering Mp, which shows pattern regularity in SMT, increases with the magnetic field H due to the suppression of the azimuthal rotational freedom. Three regions in the H-dependence of Mp are found: the zero regime, the steep increase regime and the saturated regime. In the steep increase regime, Mp shows a linear relation with H̄2, from which the susceptibility χp for the pattern ordering is obtained..
44. Fahrudin Nugroho, Tatsuhiro Ueki, Rinto Anugraha, Yoshiki Hidaka, Shoichi Kai, New measure of chaos of convective pattern in soft-mode turbulence, 4th Asian Physics Symposium 4th Asian Physics Symposium - An International Event, 10.1063/1.3537932, 293-296, 2010.12, We investigate the response of electroconvective patterns to an external magnetic field H in a homeotropic nematic system where spatiotemporal chaos called the soft-mode turbulence (SMT) occurs. We introduce new order parameter Op, obtained directly from the amplitude spectrum of the patterns. We measure the degree of regularity of patterns under influence of H using O p and compare with the pattern ordering Mp obtained from analogy with the magnetization in 2D XY model. Our new order parameter O p is well proportional to Mp..
45. Annop Klamchuen, Takeshi Yanagida, Masaki Kanai, Kazuki Nagashima, Keisuke Oka, Tomoji Kawai, Masaru Suzuki, Yoshiki Hidaka, Shoichi Kai, Impurity induced periodic mesostructures in Sb-doped SnO2 nanowires, Journal of Crystal Growth, 10.1016/j.jcrysgro.2010.08.011, 312, 21, 3251-3256, 2010.10, Impurity doping on semiconductor nanowires formed via vaporliquidsolid (VLS) mechanism has been investigated with the intention being to control the transport properties. Here we demonstrate that an addition of excess impurity dopants induces a mesostructure of long range periodic arched-shape in Sb-doped SnO2 nanowires. The microstructural and composition analysis demonstrated the importance of the presence of impurities at the growth interface during VLS growth rather than the dopant incorporation into nanowires, indicating kinetically induced mechanisms..
46. Annop Klamchuen, Takeshi Yanagida, Masaki Kanai, Kazuki Nagashima, Keisuke Oka, Tomoji Kawai, Masaru Suzuki, Yoshiki Hidaka, Shoichi Kai, Role of surrounding oxygen on oxide nanowire growth, Applied Physics Letters, 10.1063/1.3474605, 97, 7, 2010.08, The ability to control oxide nanowires via vapor-liquid-solid (VLS) mechanism remains an important challenge to explore various applications of oxide nanowires. Here we demonstrate the crucial roles of surrounding oxygen on VLS grown SnO2 nanowires. When the partial pressure of surrounding oxygen is relatively low, the oxygen mainly acts as an oxygen source, promoting VLS growth. While for relatively high oxygen partial pressures, vapor-solid (VS) growth emerges, suppressing nanowire growth. The findings as to the roles of surrounding oxygen on the inherent competition between VLS and VS growths are in principle rather universal for VLS grown nanowires of various oxides..
47. Masaru Suzuki, Yoshiki Hidaka, Takeshi Yanagida, Masaki Kanai, Tomoji Kawai, Shoichi Kai, Numerical study on the difference in mechanism between vapor-solid and vapor-liquid-solid solidification processes, Physical Review E - Statistical, Nonlinear, and Soft Matter Physics, 10.1103/PhysRevE.82.011605, 82, 1, 2010.07, In the vapor-liquid-solid (VLS) nanowire growth, nanowires can be constructed utilizing the difference in the mechanism of crystallization between the vapor-solid (VS) process (outside the solvent droplet) and the VLS process (inside the droplet). We performed a series of separate molecular dynamics simulations for a VLS system and a VS system under equivalent nonequilibrium conditions to clarify the different mechanisms of the solid growth process in both systems and to understand how a liquid substance can catalyze the solidification. The detailed observation of the chemical potential distribution during the steady solid growth state clearly outlines the processes that limit the growth rate. We found that the most dominant process limiting the growth rate is mass transport in the solvent liquid. We also show numerically and analytically that the mass transport rate is proportional to the diffusion constant and also to the solubility of in the solvent, and that a high solubility in the solvent can almost compensate for the disadvantage of a small diffusion constant. Although remarkable catalytic effect by the solvent at least in the linear nonequilibrium region could not be observed, our results suggest that the VLS process would catalyze the solid growth using liquid substance with higher solubility or in a nonlinear nonequilibrium state..
48. Yoshiki Hidaka, Yusaku Hosokawa, Noriko Oikawa, Koyo Tamura, Rinto Anugraha, Shoichi Kai, A nonequilibrium temperature and fluctuation theorem for soft-mode turbulence, Physica D: Nonlinear Phenomena, 10.1016/j.physd.2009.07.003, 239, 11, 735-738, 2010.06, Non-thermal Brownian motion of a particle for soft-mode turbulence (SMT) in the electroconvection of a nematic liquid crystal has been experimentally investigated to clarify the statistical and thermodynamical aspects of SMT, using the Lagrangian picture in hydrodynamics. The effective temperature for SMT is obtained in two different ways based on the Einstein relation and the fluctuation theorem from the diffusion due to non-thermal particle fluctuations. The temperatures from the two methods agree well and exhibit a high value of 106 K. They depend on the coarse-graining time, which reflects the anomalous properties of the macroscopic fluctuations for the SMT..
49. Rinto Anugraha, Yoshiki Hidaka, Tatsuhiro Ueki, Shoichi Kai, Symmetry-dependent defect structures in soft-mode turbulence, Physical Review E - Statistical, Nonlinear, and Soft Matter Physics, 10.1103/PhysRevE.80.041701, 80, 4, 2009.10, In the soft-mode turbulence (SMT) in electroconvection of homeotropic nematic systems, which is a kind of spatiotemporal chaos induced by nonlinear interaction between two two-dimensional (2D) XY fields, the Nambu-Goldstone modes, and the convective modes, a curious line structure called blackline has been discovered. We measured the density of the blackline as a function of control parameters, ac voltage, and frequency. By detailed observations and analysis, it is clarified that the blackline is a structure of the nematic director in the x-y plane and includes a sequence of point defects. We discussed similarity with the density of the blackline and that of the point defect in the conventional 2D XY model. The occurrence of this type of defects is only due to the symmetry in the SMT and independent of the properties of fluctuations..
50. Rinto Anugraha, Yoshiki Hidaka, Noriko Oikawa, Shoichi Kai, A transition to spatiotemporal chaos under a symmetry breaking in a homeotropic nematic system, journal of the physical society of japan, 10.1143/JPSJ.77.073001, 77, 7, 2008.07, This Letter reports a transition to spatiotemporal chaos (STC) in an electroconvective system of a homeotropic nematic liquid crystal under a symmetry breaking. The homeotropic system has a continuous symmetry which leads to the occurring of STC at a threshold for convection. When the symmetry is broken by an external field, a periodic pattern appears first and then STC appears at a higher transition point. The transition from the periodic pattern to STC is investigated by order parameters which were obtained from spectra of convective patterns. The results are compared with the recent theoretical researches for the damped Nikolaevskiy equation..
51. Rinto Anugraha, Koyo Tamura, Yoshiki Hidaka, Noriko Oikawa, Shoichi Kai, Order-disorder phase transition in a chaotic system, Physical Review Letters, 10.1103/PhysRevLett.100.164503, 100, 16, 2008.04, For soft-mode turbulence, which is essentially the spatiotemporal chaos caused by the nonlinear interaction between convective modes and Goldstone modes in electroconvection of homeotropic nematics, a type of order-disorder phase transition was revealed, in which a new order parameter was introduced as pattern ordering. We calculated the spatial correlation function and the anisotropy of the convective patterns as a 2D XY system because the convective wave vector could freely rotate in the homeotropic system. We found the hidden order in the chaotic patterns observed beyond the Lifshitz frequency fL, and a transition from a disordered to a hidden ordered state occurred at the fL with the increase of the frequency of the applied voltages..
52. Noriko Oikawa, Yoshiki Hidaka, Shoichi Kai, Controlling chaos for spatiotemporal intermittency, Physical Review E - Statistical, Nonlinear, and Soft Matter Physics, 10.1103/PhysRevE.77.035205, 77, 3, 2008.03, This paper reports the control of spatiotemporal intermittency in an electroconvective system in a nematic liquid crystal. In the spatiotemporal intermittency, an ordered structure [the defect lattice (DL)] coexists with turbulence. Control of the spatiotemporal intermittency, in which the turbulent state changes to a DL, is achieved by a few percent amplitude modulation of the applied ac voltage. The optimal control frequency is equal to the intrinsic oscillation frequency of the DL. The transition from the turbulent state to a DL occurs not by nucleation of the DL domain, but by penetration of the DL domain into the turbulent one. Control of the spatiotemporal intermittency is achieved through a resonance of the DL oscillation with respect to the modulation frequency that leads to spatial entrainment..
53. Noriko OIKAWA, Yoshiki HIDAKA and Shoichi KAI, Control of Spatiotemporal Intermittency by Parametric Resonance, 2007 International Symposium on Nonlinear Theory and its Applications Proceedings, pp. 47-50, 2007.09.
54. Yoshiki HIDAKA, Statistical Properties of Spatiotemporal Intermittency in an Electroconvective System of Nematics, Proceedings of 2nd Jogja International Physics Conference, pp. KS012-KS015, 2007.09.
55. Koyo Tamura, Rinto Anugraha, Ryohei Matsuo, Yoshiki Hidaka, Shoichi Kai, Control parameter dependence of spatial domain structures in soft-mode turbulence, journal of the physical society of japan, 10.1143/JPSJ.75.063801, 75, 6, 2006.06, Soft-mode turbulence (SMT) is a spatiotemporal chaos in electrohydrodynamic convective systems. It is caused by a nonlinear interaction between the convection mode and a Nambu-Goldstone mode, and bifurcates supercritically from a stationary uniform state. In this paper, we clarify that a spatial structure larger than a convective roll exists in SMT, which shows a patchlike domain structure characterized by wavevector directions. The dependence of the average size of the patch structure on the control parameter ε is given as ε-1/2..
56. Yoshiki Hidaka, Koyo Tamura, Shoichi Kai, Soft-mode turbulence in electroconvection of nematics, Progress of Theoretical Physics Supplement, 10.1143/PTPS.161.1, 161, 1-11, 2006.06, Soft-mode turbulence (SMT) observed in the electroconvection of a nematic liquid crystal is a first experimental example of spatiotemporal chaos (STC) due to an additional Goldstone mode. In a nematic liquid crystal with homeotropic alignment a continuous rotational symmetry is broken by a kind of buckling instability of the alignment by applying voltage (control parameter), and this spontaneous symmetry breaking leads to a Goldstone mode. Further increasing the control parameter, electroconvective instability sets in and a roll pattern could be expected to appear. SMT however ensues by the coupling of the roll pattern with the Goldstone mode. SMT has the following properties: (i) SMT is one of the rare examples of STC appearing via single supercritical bifurcation directly from a quiescent state. With decreasing the control parameter, the correlation time of the chaotic fluctuation becomes longer and diverges at the bifurcation point, that is, the fluctuations become soft, (ii) SMT is the STC in respect to the directions of convective wavevector, and patches which are the areas with the same directions appear, (iii) The averaged size of the patch, as well as the the correlation length, becomes larger with decreasing the control parameter from the above of threshold. Furthermore we have investigated transport properties in SMT by observing non-thermal "Brownian motion" in order to elucidate a fluctuation theorem in dissipative systems. This study gives us important information about SMT from a viewpoint of the Lagrangian picture which is different from the properties of the Euler picture (pattern dynamics). We presented the time-scale dependence of diffusion constants obtained by a coarse-graining. The obtained result reflects that SMT pattern has two different length scales, rolls and patches. The diffusion of particles inside a patch is anomalous, i.e. Lévy diffusion, while the diffusion of inter-patches is normal. Thus the transport property of SMT is closely related with its spatial hierarchy..
57. Noriko Oikawa, Yoshiki Hidaka, Shoichi Kai, Transition to turbulence via 2-dimensional spatiotemporal intermittency in an electroconvective system of nematics, Progress of Theoretical Physics Supplement, 10.1143/PTPS.161.320, 161, 320-323, 2006.01, The transition to turbulence via 2-dimensional spatiotemporal intermittency observed in an electroconvective system of nematics is investigated experimentally. The area fraction of total turbulent domain was continuously increased with control parameter. Dynamic hysteresis in the transition is found by measurements for various ramp rate r of the control parameter, and it is vanished for r → 0..
58. Noriko OIKAWA, Yoshiki HIDAKA and Shoichi KAI, Formation of a defect lattice in electroconvection of nematics, Physical Review E, 10.1103/PhysRevE.70.066204, 70, 6, Vol. 70, pp. 066204, 2004.12.
59. Noriko OIKAWA, Yoshiki HIDAKA and Shoichi KAI, Defect Chaos in a Convective System Limited by Domain Walls, Journal of the Physical Society of Japan, 10.1143/JPSJ.73.2917, 73, 11, 2917-2920, Vol. 73, No. 11, pp. 2917-2920, 2004.11.
60. Jong-Hoon HUH, Yusril YUSUF, Yoshiki HIDAKA and Shoichi KAI, A Periodic Director Structure of Nematic Liquid Crystals in a High-Frequency Electric Field, Molecular Crystals and Liquid Crystals, 10.1080/15421400490434586, 410, 567-575, Vol. 410, pp. 567-575, 2004.01.
61. Jong-Hoon HUH, Yusril YUSUF, Yoshiki HIDAKA and Shoichi KAI, Prewavy instability of nematic liquid crystals in a high-frequency electric field, Physical Review E, 10.1103/PhysRevE.66.031705, 66, 3, Vol. 66, 031705, 2002.01.
62. Koyo TAMURA, Yoshiki HIDAKA, Yusril YUSUF and Shoichi KAI, Anomalous diffusion and L?vy distribution of particle velocity in soft-mode turbulence in electroconvection, Physica A, 10.1016/S0378-4371(02)00494-6, 306, 1-4, 157-168, Vol. 306, pp. 157-168, 2002.01.
63. Y. Yusuf, Y. Hidaka, S. Kai, H. R. Brand, P. E. Cladis, W. Weissflog, G. Pelzl, Electric field mediated growth habits in B7, Ferroelectrics, 10.1080/00150190214430, 276, 171-178, 2002.01, The ground state of the novel liquid crystal phase formed by achiral banana-shaped nitro-molecules and known as B7 is not understood. While spirals and myelins spontaneously appear on cooling from the isotropic liquid, neither mature to form B7 monocrystals. We tried suppressing the flow associated with these growth transients by applying large electric fields to thin samples (1-4 μm thick). While a field untwists some spirals and coarsens the less mobile myelin textures, it stimulates even more flow and a B7 texture with variable but exceedingly small length scales..
64. Jong-Hoon HUH, Yoshiki HIDAKA, Yusril YUSUF, N?ndor ?BER, Tibor T?TH-KATONA, ?gnes BUKA and Shoichi KAI, Prewavy Pattern: A Director-modulation Structure in Nematic Liquid Crystals, Molecular Crystals and Liquid Crystals, 10.1080/10587250108024981, 364, 111-122, Vol. 364, pp. 111-122, 2001.11.
65. Koyo TAMURA, Yusril YUSUF, Yoshiki HIDAKA and Shoichi KAI, Nonlinear Transport and Anomalous Brownian Motion in Soft-Mode Turbulence, Journal of the Physical Society of Japan, 10.1143/JPSJ.70.2805, 70, 10, 2805-2808, Vol. 70, No. 10, pp. 2805-2808, 2001.10.
66. Yoshiki HIDAKA, Chevron-Wavy Pattern in Liquid Crystals, 数理解析研究所講究録「非線形散逸系の界面・パルス・波動」, Vol. 1191, pp. 19-24, 2001.02.
67. Jong Hoon Huh, Yoshiki Hidaka, Shoichi Kai, New classification of chevrons in electroconvection in homeotropically-aligned nematics, Molecular Crystals and Liquid Crystals Science and Technology Section A: Molecular Crystals and Liquid Crystals, 10.1080/10587250108024024, 366, 833-840, 2001.01, Two types of chevrons have been found in the conduction regime, as well as the conventional chevrons in the dielectric regime in homeotropically-aligned nematics. These two are named the defect-mediated chevron (DMC) and the defect-free chevron (DFC) by their structure changes. Two different bifurcation sequences are found with increasing the applied voltage, such as Fréedericksz transition → normal rolls → abnormal rolls → defect chaos →DMC for low frequencies and Fréedericksz transition → prewavy pattern → DFC for high frequencies. Moreover, the double periodicity of the chevrons (i.e., the short wavelength λ1 of the striated rolls and the long wavelength λ2 of the chevron bands) shows quite specific frequency dependence..
68. Jong-Hoon HUH, Yoshiki HIDAKA, Axel G. ROSSBERG, and Shoichi KAI, Pattern formation of chevrons in conduction regime in homeotropically aligned liquid crystals, Physical Review E, 10.1103/PhysRevE.61.2769, 61, 3, 2769-2776, Vol. 61, No. 3, pp. 2769-2776, 2000.03.
69. Jong-Hoon HUH, Yoshiki HIDAKA and Shoichi KAI, New Scenario to Spatio-Temporal Chaos in Normal Rolls Regime with Magnetic Field in Electroconvection of Homeotropic Nematics, Molecular Crystals and Liquid Crystals, 10.1080/10587259908026093, 328, 497-504, Vol. 328, pp. 497-504, 1999.09.
70. Tomoyuki NAGAYA, Yoshinobu SATOU, Yoshiki HIDAKA, Hiroshi ORIHARA and Yoshihiro ISHIBASHI, Dynamic Image Analysis for Electro-Hydrodynamic Convection in Nematic Liquid Crystal, Molecular Crystals and Liquid Crystals, 10.1080/10587259908026100, 328, 557-563, Vol. 328, pp. 557-563, 1999.09.
71. Yoshiki HIDAKA, Tsuyoshi FUJIMURA, Nobuaki MORI and Shoichi KAI, Pattern Formation in Elecroconvection of Nematics under Spatially-Periodic Force, Molecular Crystals and Liquid Crystals, 10.1080/10587259908026101, 328, 565-572, Vol. 328, pp. 565-572, 1999.09.
72. Jong-Hoon HUH, Yoshiki HIDAKA and Shoichi KAI, Formation Scenarios for Nonlinear Patterns in Electroconvection under Controlling Goldstone Modes in Magnetic Field, Journal of the Physical Society of Japan, 10.1143/JPSJ.68.1567, 68, 5, 1567-1577, Vol.68, No. 5, pp. 1567-1577, 1999.05.
73. Jong Hoon Huh, Yoshiki Hidaka, Shoichi Kai, Observation and determination of abnormal rolls and abnormal zigzag rolls in electroconvection in homeotropic liquid crystals, Physical Review E - Statistical Physics, Plasmas, Fluids, and Related Interdisciplinary Topics, 10.1103/PhysRevE.58.7355, 58, 6, 7355-7358, 1998.01, Direct evidence for two different types of normal rolls and of zigzag rolls in homeotropically aligned nematic liquid crystals in a magnetic field is reported. The conventional normal rolls have the reflection symmetry in the xy plane. The instability, however, breaks the reflection symmetry [Formula Presented] on the director and then the abnormal rolls are expected to be observed. We have investigated the instability experimentally and discussed it in terms of the recent numerical results by Plaut et al. [Phys. Rev. Lett. 79, 2367 (1997)]. Due to the new instability, the abnormal zigzag rolls are also found below the Lifshitz frequency..
74. Jong Hoon Huh, Yoshiki Hidaka, Shoichi Kai, Transition properties of the soft-mode turbulence in the homeotropic electro convection superimposing magnetic fields, journal of the physical society of japan, 10.1143/JPSJ.67.1948, 67, 6, 1948-1954, 1998.01, The experimental study on transition processes of the spatio-temporal chaos (STC) as well as periodic patterns in homeotropically aligned nematic liquid crystals is reported under superimposing magnetic fields with electric fields. The strong dependence of the threshold for STC on the strength of magnetic fields is observed above certain normalized voltage εth, where the two types of STC are found out below and beyond the characteristic value of the magnetic field H* = 620 G. The periodic patterns were observed for the normalized voltage ε below εth. Below H* the soft-mode turbulence appears due to the Goldstone mode related to a continuous rotational-symmetry which can be controlled by the application of H. Beyond H*, the conventional STC called defect turbulence, which is similar to STC in the planar system, is observed..
75. Yoshiki Hidaka, Jong Hoon Huh, Ken Ichi Hayashi, Shoichi Kai, Michael I. Tribelsky, Dynamical Aspects of Spatiotemporal Chaos at the Onset of Electroconvection in Homeotropic Nematics, journal of the physical society of japan, 10.1143/JPSJ.66.3329, 66, 11, 3329-3332, 1997.01, The systematic experimental study of direct transition “nonconvective state — spatiotemporal chaos” in electrohydrodynamic convection of a homeotropically aligned nematic is carried out. The transient patterns, both below and beyond the Lifshitz point, are studied and classified. The patterns initially correspond to oblique and normal rolls, respectively. In all the cases the transition to chaos undergoes slow spatiotemporal modulations of the local roll orientation. This results in the final dynamical patterns isotropic on large spatial scales. The dynamics of the final patterns are also studied with a quantitative analysis of the power spectra of turbulent modes and their autocorrelation functions. The exponential decay of the correlations in time is proved..
76. Yoshiki Hidaka, Ken Ichi Hayashi, Michael I. Tribelsky, Shoichi Kai, Dynamics of eckhaus modes in one-dimensional electroconvection patterns in nematics, Molecular Crystals and Liquid Crystals Science and Technology Section A: Molecular Crystals and Liquid Crystals, 10.1080/10587259708041848, 302, 357-362, 1997.01, The quantitative experimental study of the Eckhaus instability in one-dimensional systems is carried out, employing electrohydrodynamic convection in a nematic layer. The obtained Busse balloon is in good agreement with that predicted by the Eckhaus theory. However, the observed changes of the wavenumber for unstable roll patterns, caused by the Eckhaus instability, as well as the growth rates for the corresponding spatial modes differ dramatically from those the theory yields for the most unstable Eckhaus modes. Possible reasons for the disagreement are discussed..
77. Yoshiki Hidaka, Ken Ichi Hayashi, Shoichi Kai, Formation and dynamics of convective pattern in homeotropic system of nematic liquid crystals, Molecular Crystals and Liquid Crystals Science and Technology Section A: Molecular Crystals and Liquid Crystals, 10.1080/10587259708041852, 302, 385-390, 1997.01, Pattern dynamics in a weakly nonlinear regime near the onset of the electrohydrodynamic instability (EHDl) is experimentally investigated in the homeotropic alignment of nematic liquid crystals, of which morphology is introduced. The wavy, chain and bamboo-chevron patterns are observed in homeotropic samples as new patterns. The Busse balloon is also obtained which is quite different from the conventional balloons in EHDI in planar liquid crystals..
78. Yoshiki Hidaka, Jong Hoon Huh, Ken ichi Hayashi, Shoichi Kai, Michael I. Tribelsky, Soft-mode turbulence in electrohydrodynamic convection of a homeotropically aligned nematic layer, Physical Review E - Statistical Physics, Plasmas, Fluids, and Related Interdisciplinary Topics, 10.1103/PhysRevE.56.R6256, 56, 6, R6256-R6259, 1997.01, The experimental study of electroconvection in a homeotropically aligned nematic (MBBA) is reported. The system undergoes a supercritical bifurcation “rest state-spatiotemporal chaos.” The chaos is caused by long-wavelength modulation of the orientation of convective rolls. For the first time the observations both below and beyond the Lifshitz point are accompanied by quantitative analysis of temporal autocorrelation functions of turbulent modes. The dependence of the correlation time on the control parameter is obtained. A secondary bifurcation from normal to abnormal rolls is discussed..
79. Shoichi Kai, Ken Ichi Hayashi, Yoshiki Hidaka, Pattern forming instability in homeotropically aligned liquid crystals, Journal of physical chemistry, 10.1021/jp961539f, 100, 49, 19007-19016, 1996.12, The electrohydrodynamic pattern forming instability (EHC) driven by an ac voltage applied to a homeotropically aligned nematic liquid crystal layer is experimentally studied near onset. By controlling an external magnetic field, many different scenarios become accessible. For finite fields various regular convective structures are observed, which we call, for example, wavy, chain, and bamboo-chevron patterns. The various types are documented with the help of a phase diagram governed by the frequency and the strength of the applied ac voltage. In addition the stability regimes in the voltage-wavenumber plane (the "Busse balloon") are mapped out. One finds significant differences from the conventional planar case, for which a theoretical analysis is lacking so far. For zero magnetic field, on the other hand, no regular structure is observed, even immediately above the onset of EHC. A new spatiotemporally chaotic pattern called the soft mode turbulence directly appears via a supercritical bifurcation from the nonconvective state. This is due to the presence of the Goldstone mode related to the spontaneously broken rotational symmetry associated with the director component in the plane of the layer..
80. Shoichi Kai, Yoshiki Hidaka, Ken Ichi Hayashi, Michael I. Tribelsky, Universal Defect Dynamics in Two-Dimensional Convective Roll Patterns, journal of the physical society of japan, 10.1143/JPSJ.65.3419, 65, 11, 3419-3422, 1996.01, The process of annihilation of two point defects with opposite topological charges in a roll pattern is discussed for electrohydrodynamic convection in a nematic layer. It is shown that at the final stage of the process the distance between the centers of defects which are being annihilated varies as the square root of the time, down-counted from the annihilation moment. Such a scaling is associated with topological properties of the slowly varying complex amplitude of the order parameter and is suggested as a generic law for annihilation or spontaneous, barrierless nucleation of pairs of defects in extended systems. Experimental evidence of the scaling in the case of electrohydrodynamic convection in MBBA is obtained..
81. Yoshiki Hidaka, Hiroshi Orihara, Yoshito Miyazaki, Tomoyuki Nagaya, Yoshihiro Ishibashi, Dynamics of One-Dimensional Periodic Pattern Formation on the Electro-Hydrodynamic Convection of a Nematic Liquid Crystal, journal of the physical society of japan, 10.1143/jpsj.65.64, 65, 1, 64-69, 1996, The formation processes of a one-dimensional periodic pattern were investigated on the electrohydrodynamic convection of a nematic liquid crystal. Two kinds of processes for different initial conditions were observed. In the first initial condition the system was set to be the no-flow state in the absence of the applied field, and in the second the turbulent state under a strong field. The temporal change of the one-dimensional image intensity was measured after the amplitude of an ac electric field was jumped from these initial values to a value slightly above the critical one. The power spectrum function and the locally varying phase were calculated from the image intensity. The obtained results were compared with the numerical simulations of the diffusion equation..
82. Yoshiki Hidaka, Tomoyuki Nagaya, Hiroshi Or1Hara, Yoshihiro Ishibashi, Pattern Formation
In the Two Electro-Hydrodynamic Systems Coupled Through Free Lateral Boundaries, Molecular Crystals and Liquid Crystals Science and Technology. Section A. Molecular Crystals and Liquid Crystals, 10.1080/10587259508041700, 265, 1, 291-298, 1995.06, The interaction between the two convective systems separated by free lateral boundaries and the pattern formation have been studied. We have prepared a cell, where two identical convective subsystems with small aspect ratios are placed in the direction of the roll axis and coupled through the free lateral boundaries and the liquid crystal placed in-between. It is found that the evolution of convection in one subsystem is affected by the state of the other subsystem through the free boundaries. Moreover, the entrainment of the spatial pattern is observed..
83. Yoshiki Hidaka, Kazurou Shimokawa, Tomoyuki Nagaya, Hiroshi Orihara, Yoshihiro Ishibashi, Evolution Processes of the Williams Domain in the Electro-Hydrodynamic Systems with Free and Rigid Lateral Boundaries, journal of the physical society of japan, 10.1143/JPSJ.63.1698, 63, 5, 1698-1712, 1994.01, In the electro-hydrodynamic systems of nematic liquid crystals with free and rigid boundaries and a small aspect ratio, the pattern evolution process on applying the stepwise ac voltage was studied. The convective rolls appeared at the both lateral sides of the system, and evolved toward the center. It was found that the pattern is selected through the phase jump. The pattern in the free lateral boundary cell had more flexibility than in the rigid lateral boundary cell. The interactions between the two subsystems separated by free lateral boundary and the selection of the pattern were studied. It was found that the evolution and the selection of the pattern in a subsystem were affected by those in the other subsystem through the free boundary..
84. Yoshiki Hidaka, Hiroshi Orihara, Yoshihiro Ishibashi, The Transition from Quasi-Periodicity to Chaos in the Electro-Hydrodynamic Instability of a Nematic Liquid Crystal, journal of the physical society of japan, 10.1143/JPSJ.61.3950, 61, 11, 3950-3959, 1992.11, The electro-hydrodynamic instability was investigated in a nematic liquid crystal cell with the free boundary condition on the sides and with a small aspect ratio. In such a free lateral boundary cell, a transition from quasi-periodicity to chaos was observed by measuring the angle-deflective oscillation when the applied voltage was increased. The correlation dimension in the chaotic state was obtained from the time sequence of the transmission intensity..
85. Yoshihiro Ishibashi, Yoshiki Hidaka, On an Isomorphous Transition, journal of the physical society of japan, 10.1143/JPSJ.60.1634, 60, 5, 1634-1637, 1991.01, A phase diagram and several physical quantities related to an isomorphous transition are studied on the basis of a Landau-type free energy function. Relationship with a two-sublattice model including an asymmetric double minimum potential is discussed..