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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.

Koibuchi H.,Ibaraki National College of Technology | Shobukhov A.,Moscow State University
Physica A: Statistical Mechanics and its Applications | Year: 2014

We study phase transition of self-avoiding fluid surface model on dynamically triangulated lattices using the Monte Carlo simulation technique. We report the continuous transition between the branched polymer and inflated phases at Δp=0, where Δp(=pin-pout) is the pressure difference between the inner and outer sides of the surface. This transition is characterized by almost discontinuous change of the enclosed volume vs. the variations of the bending rigidity κ and the pressure difference Δp. No surface fluctuation transition accompanies this transition up to the surface with the number of vertices N=2562. © 2014 Elsevier B.V. All rights reserved.

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.

Koibuchi H.,Ibaraki National College of Technology
Nuclear Physics B | Year: 2010

We numerically study a triangulated surface model in R2 by taking into account a viewpoint of string model. The models are defined by a mapping X from a two-dimensional surface M to R2, where the mapping X and the metric g of M are the dynamical variables. The sum over g in the partition function is simulated by the sum over bond lengths and deficit angles by using the Regge calculus technique, and the sum over g is defined to be performed independently of the sum over X. We find that the model undergoes a first-order transition of surface fluctuations, which accompanies a collapsing transition, and that the transitions are reflected in the internal geometry of surface. Fluid surface models are also studied on dynamically triangulated surfaces, and the transitions are found to be of second order. The order of the transition remains unchanged from that of the conventional model defined only by the variable X both in the fixed-connectivity and the fluid models. © 2010 Elsevier B.V.

Kikuchi M.,Ibaraki National College of Technology
Proceedings of the IASTED International Conference on Modelling, Identification and Control | Year: 2010

This paper proposes a physiologic mathematical model for a minimal neural network. Then, the mathematical models of neurocyte may automatically form small-neural networks if being able to use self-organization algorithm in the future. The results in this paper indicate that this simulation model was able to simulate "NGF taxis of axon" known as one of characteristics of the neurocyte. This "taxis" is one of the significant functions for control of self-organization. In particular, this mathematical model includes potentiality that is able to design the small-neural networks that can mimic functions of insect's simple-nervous systems autonomously. There is an expectation that the results can be applied to the improvement of the self-growth miniature robot's controller in the future. However, this mathematical model has limitations in that the computing time to look for a network that satisfies the necessary conditions increases when a more complex neural network is required.

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.

Matsuhisa T.,Ibaraki National College of Technology
International Journal of Intelligent Information and Database Systems | Year: 2012

This paper investigates the role of common-knowledge in the principal-agent model under uncertainty. We treat the problem: How epistemic conditions will be able to settle a moral hazard in team in the principal-agent model under uncertainty. We shall propose a resolution programme for the moral hazard in the principal-agent model by common-knowledge. Let us assume that the agents have the knowledge structure induced from a binary relation associated with the multi-modal logic S5n or S4n. We show that the moral hazard can be resolved in the principal-agent model under uncertainty if the agents commonly know all their own costs. Copyright © 2012 Inderscience Enterprises Ltd.

Hori T.,Ibaraki National College of Technology
IEEE Transactions on Circuits and Systems II: Express Briefs | Year: 2016

It has been found that 2-D discrete diamond-shaped frequency distributions used in the harmonic balance method can be calculated by 1-D sampling, where the number of sampling points can be equal to that of nonzero (NZ) frequency components. The reciprocal vector of the periodicity matrix of tiling is chosen as the unit step of the 1-D sampling. However, in general, reciprocal vectors cannot always be the unit vectors of 1-D samplings for 2-D discrete frequency distributions. The condition for a reciprocal vector to be a unit step of 1-D sampling for 2-D discrete frequency distributions with tiling capability is examined in this brief. The results show that the condition is that two things are satisfied simultaneously for the periodicity matrix of tiling, [M]. When [M] is expressed as [M]=[A][D][B] in the Smith normal form, [A] and [B] are unimodular matrices, and [D] is an integer-valued diagonal matrix. One is that d1 of [D] is 1. The other is that ([A]{-1}){2,1} and {d2} of [D] are congruent. When the condition is satisfied, the reciprocal vector {T}{1} made from [M]{-1} can be a unit step of 1-D sampling, where 1-D discrete Fourier transform can be used in the calculation, and the number of sampling points is equal to that of NZ frequency components. © 2004-2012 IEEE.

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.

Wakamatsu T.,Ibaraki National College of Technology
Review of Scientific Instruments | Year: 2015

The article presents a method and an apparatus for the characterization of protein aggregation under an applied internal electric field. The method is based on a forward light scattering technique that is highly sensitive to aggregates in pre-crystalline protein solutions. Transparent conductive films are used as electrodes for a planar thin sample cell, which enables precise measurement of the forward light scattering at small angles through the electrodes. Evaluation of the protein aggregation under applied electric fields was demonstrated for a model lysozyme protein. In situ measurements of crystallizing lysozyme solutions under a low applied voltage revealed that the forward static light scattering profiles changed with time into power law profiles. This indicates the formation of lysozyme fractal clusters under applied electric fields in the pre-crystalline state. The method and the apparatus presented here can sensitively evaluate the promotion process in protein crystallization under an applied electric field. © 2015 AIP Publishing LLC.

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