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Koibuchi H.,Ibaraki National College of Technology
Journal of Statistical Physics | Year: 2010

Using the Wang-Landau flat histogram Monte Carlo (FHMC) simulation technique, we were able to study two types of triangulated spherical surface models in which the two-dimensional extrinsic curvature energy is assumed in the Hamiltonian. The Gaussian bond potential is also included in the Hamiltonian of the first model, but it is replaced by a hard-wall potential in the second model. The results presented in this paper are in good agreement with the results previously reported by our group. The transition of surface fluctuations and collapsing transition were studied using the canonical Metropolis Monte Carlo simulation technique and were found to be of the first-order. The results obtained in this paper also show that the FHMC technique can be successfully applied to triangulated surface models. It is non-trivial whether the technique is applicable or not to surface models because the simulations are performed on relatively large surfaces. © 2010 Springer Science+Business Media, LLC. Source

Koibuchi H.,Ibaraki National College of Technology
Physics Letters, Section A: General, Atomic and Solid State Physics | Year: 2016

We numerically check that the surface tension of membranes is independent of the shape of surface boundary. The surface tension is calculated by means of the Monte Carlo simulation technique on two types of cylinders made of rubans of size L1 and L2, where the rubans are the same for the projected area and different in the ratio L1/L2. The difference of the surface tension disappears in the thermodynamic limit in both models of Helfrich-Polyakov and Landau-Ginzburg. © 2016 Elsevier B.V. All rights reserved. Source

Burrard-Lucas M.,University of Oxford | Free D.G.,University of Oxford | Sedlmaier S.J.,University of Oxford | Wright J.D.,University of Oxford | And 8 more authors.
Nature Materials | Year: 2013

The discovery of high-temperature superconductivity in a layered iron arsenide has led to an intensive search to optimize the superconducting properties of iron-based superconductors by changing the chemical composition of the spacer layer between adjacent anionic iron arsenide layers. Superconductivity has been found in iron arsenides with cationic spacer layers consisting of metal ions (for example, Li +, Na +, K +, Ba 2+) or PbO- or perovskite-type oxide layers, and also in Fe 1.01 Se (ref.8) with neutral layers similar in structure to those found in the iron arsenides and no spacer layer. Here we demonstrate the synthesis of Li x (NH 2) y (NH 3) 1-y Fe 2 Se 2 (x∼0.6; y∼0.2), with lithium ions, lithium amide and ammonia acting as the spacer layer between FeSe layers, which exhibits superconductivity at 43(1)K, higher than in any FeSe-derived compound reported so far. We have determined the crystal structure using neutron powder diffraction and used magnetometry and muon-spin rotation data to determine the superconducting properties. This new synthetic route opens up the possibility of further exploitation of related molecular intercalations in this and other systems to greatly optimize the superconducting properties in this family. Source

Koibuchi H.,Ibaraki National College of Technology
Journal of Physics: Conference Series | Year: 2013

In this paper, we study a new surface model for anisotropic membranes. The model is characterized by an interaction between the surface and a three-dimensional tilt order, of which projected components on the surface are recognized as a vector filed. This vector field defines a Finsler metric on the surface, and consequently the length unit on the surface becomes dependent on the position and direction. The induced interaction dynamically alters the surface tension and the bending rigidity. We numerically find that the tilts form the Kosterlitz-Thouless and low temperature configurations, which correspond to two different anisotropic phases such as disk and tubular on both of the connection-fixed and dynamically triangulated surfaces. The internal tilt order plays an important role for those anisotropic configurations. © Published under licence by IOP Publishing Ltd. Source

Wakamatsu T.,Ibaraki National College of Technology
Applied Physics Letters | Year: 2011

It is presented that a forward light scattering technique is highly sensitive to aggregation in crystallizing lysozyme solutions. Static light scattering in the crystallizing protein solutions has a characteristic radiation pattern that largely differs from that of small size silica particles dispersed in water. A method to evaluate aggregate formation was demonstrated from the dependence of forward light scattering on a precipitant concentration added to a lysozyme solution. These measurements provide possibilities for characterizing protein aggregation in crystallization process. © 2011 American Institute of Physics. Source

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