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Tokyo Institute of Technology is a national top-tier research university located in Greater Tokyo Area, Japan. Tokyo Tech is the largest institution for higher education in Japan dedicated to science and technology. Tokyo Tech enrolled 4,850 undergraduates and 5,006 graduate students for 2009–2010. It employs around 1,400 faculty members.Tokyo Tech's main campus is located at Ōokayama on the boundary of Meguro and Ota, with its main entrance facing the Ōokayama Station. Other campuses are located in Nagatsuta and Tamachi. Tokyo Tech is organised into 6 schools, within which there are over 40 departments and research centres.Operating the world-class supercomputer Tsubame 2.0, and taking a breakthrough in high-temperature superconductivity, Tokyo Tech is a major centre for supercomputing technology and condensed matter research in the world.Tokyo Tech is a member of LAOTSE, an international network of leading universities in Europe and Asia exchanging students and senior scholars. In 2011 it celebrated the 130th anniversary of its founding. Wikipedia.

Kawasaki M.,University of Tokyo | Saikawa K.,Tokyo Institute of Technology | Sekiguchi T.,Helsinki Institute of Physics
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2015

The cosmological scenario where the Peccei-Quinn symmetry is broken after inflation is investigated. In this scenario, topological defects such as strings and domain walls produce a large number of axions, which contribute to the cold dark matter of the Universe. The previous estimations of the cold dark matter abundance are updated and refined based on the field-theoretic simulations with improved grid sizes. The possible uncertainties originated in the numerical calculations are also discussed. It is found that axions can be responsible for the cold dark matter in the mass range ma=(0.9-1.4)×10-4eV for the models with the domain wall number NDW=1, and ma≈O(10-4-10-2)eV with a mild tuning of parameters for the models with NDW>1. Such higher mass ranges can be probed in future experimental studies. © 2015 American Physical Society.

Akagi H.,Tokyo Institute of Technology | Kitada R.,Chubu Electric Power Co.
IEEE Transactions on Power Electronics | Year: 2011

This paper discusses the control and design of the 6.6-kV back-to-back (BTB) system combining bidirectional isolated dc/dc converters and modular multilevel cascade pulsewidth modulation (PWM) converters. The system consists of multiple converter cells connected in cascade per phase at both front ends. Each converter cell consists of a bidirectional isolated medium-frequency dc/dc converter and two voltage-source H-bridge (single-phase full-bridge) PWM converters. Extremely low-voltage steps bring a significant reduction in harmonics and electromagnetic interference emissions to the BTB system. This paper designs, constructs, and tests a single-phase downscaled BTB system rated at 120 V and 3.3 kW to verify the viability and effectiveness, leading to the actual system. © 2011 IEEE.

Inoue S.,Korea Astronomy and Space Science Institute 776 | Inoue S.,Hebrew University of Jerusalem | Saitoh T.R.,Tokyo Institute of Technology
Monthly Notices of the Royal Astronomical Society | Year: 2014

We examine a possible formation scenario of galactic thick discs with numerical simulations. Thick discs have previously been argued to form in clumpy disc phase in the high-redshift Universe, which host giant clumps of ≲109 M⊙ in their highly gas-rich discs. We performed N-body/smoothed particle hydrodynamics simulations using isolated galaxy models for the purpose of verifying whether dynamical and chemical properties of the thick discs formed in such clumpy galaxies are compatible with observations. The results of our simulations seem nearly consistent with observations in dynamical properties such as radial and vertical density profiles, significant rotation velocity lag with height and distributions of orbital eccentricities. In addition, the thick discs in our simulations indicate nearly exponential dependence of σθ and σz with radius, nearly isothermal kinematics in vertical direction and negligible metallicity gradients in radial and vertical directions. However, our simulations cannot reproduce altitudinal dependence of eccentricities, metallicity relations with eccentricities or rotation velocities, which shows striking discrepancy from recent observations of the Galactic thick disc. From this result, we infer that the clumpy disc scenario for thick-disc formation would not be suitable at least for the Milky Way. Our study, however, cannot reject this scenario for external galaxies if not all galaxies form their thick discs by the same process. In addition, we found that a significant fraction of thick-disc stars forms in giant clumps. © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.

Real-time distance measurement of a moving object with high accuracy and high resolution using an ultrasonic wave is difficult due to the influence of the Doppler effect or the limit of the calculation cost of signal processing. An over-sampling signal processing method using a pair of LPM signals has been proposed for ultrasonic distance and velocity measurement of moving objects with high accuracy and high resolution. The proposed method consists of cross correlation by single-bit signal processing, high-resolution Doppler velocity estimation with wide measurement range and low-calculation-cost Doppler-shift compensation. The over-sampling cross-correlation function is obtained from cross correlation by single-bit signal processing with low calculation cost. The Doppler velocity and distance of the object are determined from the peak interval and peak form in the cross-correlation function by the proposed method of Doppler velocity estimation and Doppler-shift compensation. In this paper, the proposed method of Doppler-shift compensation is improved. Accuracy of the determined distance was improved from approximately within ±140 μm in the previous method to approximately within ±10 μm in computer simulations. Then, the proposed method of Doppler velocity estimation is evaluated. In computer simulations, accuracy of the determined Doppler velocity and distance were demonstrated within ±8.471 mm/s and ±13.87 μm. In experiments, Doppler velocities of the motorized stage could be determined within ±27.9 mm/s. © 2012 Elsevier B.V. All rights reserved.

Wakai F.,Tokyo Institute of Technology | Guillon O.,Friedrich - Schiller University of Jena
Acta Materialia | Year: 2014

The sintering stress is a driving force for morphological evolution of pores in sintering, and can be determined from knowledge of the microstructure. The sintering stress of non-equilibrium, non-uniform and non-isotropic porous glass films cast and sintered on rigid substrates was computed from synchrotron X-ray microtomography data. This method was able to show how the inhomogeneous distribution of local density at the particle scale led to a difference in local sintering stress. The anisotropic microstructure in the film was correlated to the deviatoric components of the sintering stress, which were defined by surface energy tensor. The topological evolution of pore structure was characterized by genus and Euler characteristic. © 2013 Elsevier Inc. All rights reserved.

Somiya K.,Tokyo Institute of Technology
Classical and Quantum Gravity | Year: 2012

The construction of the Japanese second-generation gravitational-wave detector KAGRA (previously called LCGT) has been started. In the next 67 years, we will be able to observe the spacetime ripple from faraway galaxies. KAGRA is equipped with the latest advanced technologies. The entire 3 km long detector is located in the underground to be isolated from the seismic motion, the core optics are cooled down to 20 K to reduce thermal fluctuations and quantum non-demolition techniques are used to decrease quantum noise. In this paper, we introduce the detector configuration of KAGRA, its design, strategy and downselection of parameters. © 2012 IOP Publishing Ltd.

Akagi H.,Tokyo Institute of Technology
IEEE Transactions on Power Electronics | Year: 2011

This paper discusses the modular multilevel cascade converter (MMCC) family based on cascade connection of multiple bidirectional chopper cells or single-phase full-bridge cells. The MMCC family is classified from circuit configuration as follows: the single-star bridge cells (SSBC); the single-delta bridge cells (SDBC); the double-star chopper cells (DSCC); and the double-star bridge cells (DSBC). The term MMCC corresponds to a family name in a person while, for example, the term SSBC corresponds to a given name. Therefore, the term MMCC-SSBC can identify the circuit configuration without any confusion. Among the four MMCC family members, the SSBC and DSCC are more practical in cost, performance, and market than the others although a distinct difference exists in application between the SSBC and DSCC. This paper presents application examples of the SSBC to a battery energy storage system (BESS), the SDBC to a static synchronous compensator (STATCOM) for negative-sequence reactive-power control, and the DSCC to a motor drive for fans and blowers, along with their experimental results. © 2011 IEEE.

Tazaki Y.,Nagoya University | Imura J.-I.,Tokyo Institute of Technology
IEEE Transactions on Automatic Control | Year: 2012

This paper proposes a computational method for the feasibility check and design of discrete abstract models of nonlinear dynamical systems. First, it is shown that a given discrete-time dynamical system can be transformed into a finite automaton by embedding a quantizer into its state equation. Under this setting, a sufficient condition for approximate bisimulation in infinite steps of time between the concrete model and its discrete abstract model is derived. The condition takes the form of a set of linear inequalities and thus can be checked efficiently by a linear programming solver. Finally, the iterative refinement algorithm, which generates a discrete abstract model under a given error specification, is proposed. The algorithm is guaranteed to terminate in finite iterations. © 2011 IEEE.

Liu H.-C.,Tokyo Institute of Technology | Liu L.,Tongji University | Wu J.,Tongji University
Materials and Design | Year: 2013

Nowadays, selection of an optimal material has become a challenging task for the designers in the design and development of products. Material selection for an engineering design can be viewed as a complicated multi-criteria decision making (MCDM) problem which requires consideration of a number of available materials and conflicting tangible and intangible selection criteria. Moreover, decision makers tend to use multigranularity linguistic term sets for expressing their assessments because of their different backgrounds and preferences, some of which may be uncertain and incomplete. Therefore, this paper presents an interval 2-tuple linguistic VIKOR (ITL-VIKOR) method for solving the material selection problem under uncertain and incomplete information environment. The new method can not only model the uncertainty and diversity of decision makers' assessment information but also consider the subjective and objective weights of criteria simultaneously in the material selection process. The method has exact characteristic and can avoid information distortion and losing in the linguistic information processing. Finally, two examples are included to demonstrate the feasibility and practicability of the proposed method. © 2013 Elsevier Ltd.

Fujita H.,Tokyo Institute of Technology | Uchida N.,Mitsui Engineering and Shipbuilding Co. | Ozaki K.,Mitsui Engineering and Shipbuilding Co.
IEEE Transactions on Power Electronics | Year: 2011

This paper proposes a new zone-control induction heating (ZCIH) system consisting of two or more sets of a high-frequency inverter unit and a work coil. The work coils are wound around a single susceptor as close as possible to reduce a leakage magnetic flux. The inverters independently control the amplitude of each coil current to adjust the power provided to the work coil and/or the heat generated in each zone of the susceptor. As a result, the ZCIH system enables a temperature uniformity not only in a heating-up period but also in a temperature-maintaining period. Theoretical analysis derives the control performance of the current amplitude, and implies that the phase-angle control of the coil current is required to adjust the current amplitude in a wide range. This paper presents experimental results obtained from a laboratory setup and a six-zone prototype for semiconductor processing. © 2011 IEEE.

Oka M.,Tokyo Institute of Technology
Nuclear Physics A | Year: 2012

Origin of the short-range baryon-baryon interactions is discussed from the quark substructure viewpoints of baryons. It is pointed out that the generalized nuclear force, recently obtained from the lattice QCD calculations, can be interpreted at short distances by the combinatory effects of the Pauli exclusion principle and the color-magnetic spin-spin interactions among the quarks. Classifications according to the spin-flavor SU(6) symmetry representations give us a general guidance on the features of the short-range interactions. The SU(6) analysis of the three-body baryon interactions reveals that the genuine three-body force is repulsive at short distances due to the quark antisymmetrization. © 2012 Elsevier B.V.

Yoshida N.,Tokyo Institute of Technology | Kanda J.,Tokyo University of Marine Science and Technology
Science | Year: 2012

Ongoing radionuclide monitoring and tracking efforts are required following the nuclear accident at the Fukushima Daiichi Nuclear Power Plant.

Shiga N.,Japan Science and Technology Agency | Shiga N.,Tokyo Institute of Technology | Takeuchi M.,University of Tokyo
New Journal of Physics | Year: 2012

A new method is proposed to reduce the frequency noise of a local oscillator to the level of white phase noise by maintaining (not destroying by projective measurement) the coherence of the ensemble pseudo-spin of atoms over many measurement cycles. This method, which we call 'atomic phase lock (APL)', uses weak measurement to monitor the phase in the Ramsey method and repeat the cycle without initialization of the phase. APL will achieve white phase noise as long as the noise accumulated during dead time and the decoherence are smaller than the measurement noise. A numerical simulation confirmed that with APL, the Allan deviation is averaged down at a maximum rate that is proportional to the inverse of the total measurement time, τ -1. In contrast, current atomic clocks that use projection measurement suppress the noise only to the white frequency noise level, in which case the Allan deviation scales as τ -1/2. Faraday rotation is one way to achieve weak measurement for APL. The strength of Faraday rotation with 171Yb + ions trapped in a linear rf-trap is evaluated, and the performance of APL is discussed. The main source of decoherence is a spontaneous emission, induced by the probe beam for Faraday rotation measurement. The Faraday rotation measurement can be repeated until the decoherence becomes comparable to the signal-to-noise ratio of the measurement. The number of cycles for a realistic experimental parameter is estimated to be ∼100. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.

Ando M.,Tokyo Institute of Technology
IEICE Transactions on Communications | Year: 2010

Design of high gain and high efficiency antennas is one of the key challenges in antenna engineering and especially in millimeter wave communication systems. Various types of planar waveguide arrays with series-fed traveling wave operation have been developed in Tokyo Tech with the special focus upon efficiency enhancement as well as reduction of fabrication cost. In this review, four kinds of single layer waveguide arrays characterized with the series fed travelling wave operation are surveyed first. To cope with the bandwidth narrowing effects due to long line effects associated with the series fed operation, authors have introduced partially corporate feed embedded in the single layer waveguide. They further extended the study to cover fully corporate feed arrays with multiple layer waveguide as well; a new fabrication technique of diffusion bonding of laminated thin plates has the potential to realize the low cost mass production of multi-layer structures for the millimeter wave application. Secondly, the novel methods for loss evaluation of copper plate substrate are established for the design of post-wall waveguide arrays where dielectric loss and conductor loss is determined in wide range of millimeter wave band, by using the Whispering gallery mode resonator. This enables us to design the planar arrays with the loss taken into account. Finally, the planar arrays are now applied to two kinds of systems in the Tokyo Tech millimeter wave project; the indoor short range file-transfer systems and the outdoor communication systems for the medium range backhaul links. The latter has been field-tested in the model network built in Tokyo Tech Ookayama campus. Early stage progress of the project including unique propagation data is also reported. Copyright © 2010 The Institute of Electronics, Information and Communication Engineers.

Akagi H.,Tokyo Institute of Technology | Matsumura I.,Railway Technical Research Institute
IEEE Transactions on Industry Applications | Year: 2011

This paper presents an intensive discussion on an overvoltage appearing at the motor terminals of an adjustable-speed drive that consists of a voltage-source pulsewidth-modulated inverter, an induction motor, and a three-phase symmetric long cable. It describes a design procedure for a simple passive electromagnetic-interference filter based on parallel connection of an inductor and a resistor, which is intended for mitigating the overvoltage at the motor terminals. The modeling of the cable and the motor is characterized by focusing on the natural frequency or ringing frequency inherent in the cable used, which is inversely proportional to cable length. Impedance mismatch at the inverter and motor terminals causes the overvoltage that may reach double the inverter dc-link voltage. The effectiveness and validity of the simple design procedure of the filter are confirmed on the 400-V 15-kW experimental system with either a 100- or 200-m-long cable, as well as on computer simulation based on the modeling of the cable and the motor. © 2011 IEEE.

Watanabe S.,Tokyo Institute of Technology
Journal of Machine Learning Research | Year: 2010

In regular statistical models, the leave-one-out cross-validation is asymptotically equivalent to the Akaike information criterion. However, since many learning machines are singular statistical models, the asymptotic behavior of the cross-validation remains unknown. In previous studies, we established the singular learning theory and proposed a widely applicable information criterion, the expectation value of which is asymptotically equal to the average Bayes generalization loss. In the present paper, we theoretically compare the Bayes cross-validation loss and the widely applicable information criterion and prove two theorems. First, the Bayes cross-validation loss is asymptotically equivalent to the widely applicable information criterion as a random variable. Therefore, model selection and hyperparameter optimization using these two values are asymptotically equivalent. Second, the sum of the Bayes generalization error and the Bayes cross-validation error is asymptotically equal to 2λ/n, where λ is the real log canonical threshold and n is the number of training samples. Therefore the relation between the cross-validation error and the generalization error is determined by the algebraic geometrical structure of a learning machine. We also clarify that the deviance information criteria are different from the Bayes cross-validation and the widely applicable information criterion. © 2010 Sumio Watanabe.

Ishii H.,Tokyo Institute of Technology | Tempo R.,CNR Institute of Electronics, Computer and Telecommunication Engineering
IEEE Transactions on Automatic Control | Year: 2010

In the search engine of Google, the PageRank algorithm plays a crucial role in ranking the search results. The algorithm quantifies the importance of each web page based on the link structure of the web. We first provide an overview of the original problem setup. Then, we propose several distributed randomized schemes for the computation of the PageRank, where the pages can locally update their values by communicating to those connected by links. The main objective of the paper is to show that these schemes asymptotically converge in the mean-square sense to the true PageRank values. A detailed discussion on the close relations to the multi-agent consensus problems is also given. © 2010 IEEE.

Kobayashi K.,Japan Advanced Institute of Science and Technology | Imura J.-I.,Tokyo Institute of Technology
Journal of Process Control | Year: 2012

As is well known, the computational complexity in the mixed integer programming (MIP) problem is one of the main issues in model predictive control (MPC) of hybrid systems such as mixed logical dynamical systems. Thus several efficient MIP solvers such as multi-parametric MIP solvers have been extensively developed to cope with this problem. On the other hand, as an alternative approach to this issue, this paper addresses how a deterministic finite automaton, which is a part of a hybrid system, should be expressed to efficiently solve the MIP problem to which the MPC problem is reduced. More specifically, a modeling method to represent a deterministic finite automaton in the form of a linear state equation with a smaller set of binary input variables and binary linear inequalities is proposed. After a motivating example is described, a derivation procedure of a linear state equation with linear inequalities representing a deterministic finite automaton is proposed as three steps; modeling via an implicit system, coordinate transformation to a linear state equation, and state feedback binarization. Various significant properties on the proposed modeling are also presented throughout the proofs on the derivation procedure. © 2012 Elsevier Ltd. All rights reserved.

Ishii H.,Tokyo Institute of Technology | Tempo R.,CNR Institute of Electronics, Computer and Telecommunication Engineering | Bai E.-W.,University of Iowa | Bai E.-W.,Queens University of Belfast
IEEE Transactions on Automatic Control | Year: 2012

The PageRank algorithm employed at Google assigns a measure of importance to each web page for rankings in search results. In our recent papers, we have proposed a distributed randomized approach for this algorithm, where web pages are treated as agents computing their own PageRank by communicating with linked pages. This paper builds upon this approach to reduce the computation and communication loads for the algorithms. In particular, we develop a method to systematically aggregate the web pages into groups by exploiting the sparsity inherent in the web. For each group, an aggregated PageRank value is computed,which can then be distributed among the group members. We provide a distributed update scheme for the aggregated PageRank along with an analysis on its convergence properties. The method is especially motivated by results on singular perturbation techniques for large-scale Markov chains and multi-agent consensus. A numerical example is provided to illustrate the level of reduction in computation while keeping the error in rankings small. © 1963-2012 IEEE.

Murata T.,Tokyo Institute of Technology
Proceedings of the 19th International Conference on World Wide Web, WWW '10 | Year: 2010

Online social media such as delicious and digg are represented as tripartite networks whose vertices are users, tags, and resources. Detecting communities from such tripartite networks is practically important. Modularity is often used as the criteria for evaluating the goodness of network divisions into communities. For tripartite networks, Neubauer defines a tripartite modularity which extends Murata's bipartite modularity. However, Neubauer's tripartite modularity still uses projections and it will lose information that original tripartite networks have. This paper proposes new tripartite modularity for tripartite networks that do not use projections. Experimental results show that better community structures can be detected by optimizing our tripartite modularity. © 2010 Copyright is held by the author/owner(s).

Ishijima S.,Tokyo Institute of Technology
Cell Structure and Function | Year: 2012

The change in the flagellar waves of spermatozoa from a tunicate and sea urchins was examined using high-speed video microscopy to clarify the regulation of localized sliding between doublet microtubules in the axoneme. When the tunicate Ciona spermatozoa attached to a coverslip surface by their heads in seawater or they moved in seawater with increased viscosity, the planar waves of the sperm flagella were converted into left-handed helical waves. On the other hand, conversion of the planar waves into helical waves in the sea urchin Hemicentrotus spermatozoa was not seen in seawater with an increased viscosity as well as in ordinary seawater. However, the sea urchin Clypeaster spermatozoa showed the conversion, albeit infrequently, when they thrust their heads into seawater with an increased viscosity. The chirality of the helical waves of the Clypeaster spermatozoa was right-handed. When Ciona spermatozoa swam freely near a glass surface, they moved in relatively large circular paths (yawing motion). There was no difference in the proportion of spermatozoa yawing in either a clockwise or counterclockwise direction when viewed from above, which was also different from that of the sea urchin spermatozoa. These observations suggest that the planar waves generally observed on the sperm flagella are mechanically regulated, although their stability must depend on the Ca 2+ concentration in the cell. Furthermore, the chirality of the helical waves may be determined by the intracellular Ca 2+ concentration and changed by transmitting the localized active sliding between the doublet microtubules around the axoneme in an alternative direction. © 2012 by Japan Society for Cell Biology.

Nishida Y.,Tokyo Institute of Technology
Physical Review Letters | Year: 2015

Recently it has been proposed that three-component Fermi gases may exhibit a new type of crossover physics in which an unpaired Fermi sea of atoms smoothly evolves into that of trimers in addition to the ordinary BCS-BEC crossover of condensed pairs. Here we study its corresponding polaron problem in which a single impurity atom of one component interacts with condensed pairs of the other two components with equal populations. By developing a variational approach in the vicinity of a narrow Feshbach resonance, we show that the impurity atom smoothly changes its character from atom to trimer with increasing the attraction and eventually there is a sharp transition to dimer. The emergent polaronic atom-trimer continuity can be probed in ultracold atoms experiments by measuring the impurity spectral function. Our novel crossover wave function properly incorporating the polaronic atom-trimer continuity will provide a useful basis to further investigate the phase diagram of three-component Fermi gases in more general situations. © 2015 American Physical Society.

Yasui S.,Tokyo Institute of Technology
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2015

Transition decay widths by one-pion emissions for excited heavy baryons with a single heavy (charm and bottom) quark are investigated by following the heavy-quark symmetry and its breaking effects at O(1/M) for a heavy-baryon mass M. Based on heavy-baryon effective theory, interaction Lagrangians for the heavy baryons with an axial-vector current induced by a pion are constructed. We show that the transition decay widths in several channels are related up to O(1/M). The results will be useful in the experimental study of excited heavy baryons. © 2015 American Physical Society.

Berrar D.,Tokyo Institute of Technology
Knowledge and Information Systems | Year: 2016

In the era of big data, both class labels and covariates may result from proprietary algorithms or ground models. The predictions of these ground models, however, are not the same as the unknown ground truth. Thus, the automatically generated class labels are inherently uncertain, making subsequent supervised learning from such data a challenging task. Fine-tuning a new classifier could mean that, at the extreme, this new classifier will try to replicate the decision heuristics of the ground model. However, few new insights can be expected from a model that tries to merely emulate another one. Here, we study this problem in the context of click fraud prediction from highly skewed data that were automatically labeled by a proprietary detection algorithm. We propose a new approach to generate click profiles for publishers of online advertisements. In a blinded test, our ensemble of random forests achieved an average precision of only 36.2 %, meaning that our predictions do not agree very well with those of the ground model. We tried to elucidate this discrepancy and made several interesting observations. Our results suggest that supervised learning from automatically labeled data should be complemented by an interpretation of conflicting predictions between the new classifier and the ground model. If the ground truth is not known, then elucidating such disagreements might be more relevant than improving the performance of the new classifier. © 2015, Springer-Verlag London.

Aziz M.,Tokyo Institute of Technology
International Journal of Hydrogen Energy | Year: 2016

An integrated system for hydrogen production, storage, and power generation from microalgae using enhanced process integration technology is proposed. Enhanced process integration has two core technologies: exergy recovery and process integration. Exergy recovery is performed through exergy elevation and heat coupling to minimize exergy destruction. The unrecoverable energy/heat in a single process is recovered and used in other processes through process integration. The proposed integrated system includes supercritical water gasification, hydrogen separation, hydrogenation, and a combined cycle. The microalga Chlorella vulgaris is used for modeling and evaluation. Microalgae are converted to syngas, then separated to produce highly pure hydrogen. To store the produced hydrogen, the toluene-methylcyclohexane cycle as a liquid organic hydrogen carrier is adopted. The remaining gas is used as fuel for combustion in the combined cycle to generate electricity. The effects of the fluidization velocity and gasification pressure on energy efficiency are evaluated. From process modeling and calculation, high total energy efficiency (higher than 60%), including electricity generation efficiency of about 40%, can be realized. © 2015 Hydrogen Energy Publications, LLC.

Burns P.C.,University of Notre Dame | Ikeda Y.,Tokyo Institute of Technology | Czerwinski K.,University of Nevada, Las Vegas
MRS Bulletin | Year: 2010

Actinide solid-state and coordination chemistry has advanced through unexpected results that have further revealed the complex nature of the 5f elements. Nanoscale control of actinide materials is emerging, as shown by the creation of a considerable range of cluster and tubular topologies. Departures from established structural trends for actinyl ions are provided by cation-cation interactions in which an O atom of one actinyl ion is an equatorial ligand of a bipyramid of another actinyl ion. The solid-state structural complexity of actinide materials has been further demonstrated by open framework materials with interesting properties. The U(VI) tetraoxide core has been added to this cation's repertoire of coordination possibilities. The emergence of pentavalent uranium solid-state and coordination chemistry has resulted from the prudent selection of ligands. Finally, analogues of the uranyl ion have challenged our understanding of this normally unreactive functional group.

Yamazaki K.,Tokyo Institute of Technology
Machine Learning | Year: 2016

Hierarchical parametric models consisting of observable and latent variables are widely used for unsupervised learning tasks. For example, a mixture model is a representative hierarchical model for clustering. From the statistical point of view, the models can be regular or singular due to the distribution of data. In the regular case, the models have the identifiability; there is one-to-one relation between a probability density function for the model expression and the parameter. The Fisher information matrix is positive definite, and the estimation accuracy of both observable and latent variables has been studied. In the singular case, on the other hand, the models are not identifiable and the Fisher matrix is not positive definite. Conventional statistical analysis based on the inverse Fisher matrix is not applicable. Recently, an algebraic geometrical analysis has been developed and is used to elucidate the Bayes estimation of observable variables. The present paper applies this analysis to latent-variable estimation and determines its theoretical performance. Our results clarify behavior of the convergence of the posterior distribution. It is found that the posterior of the observable-variable estimation can be different from the one in the latent-variable estimation. Because of the difference, the Markov chain Monte Carlo method based on the parameter and the latent variable cannot construct the desired posterior distribution. © 2015, The Author(s).

Ando T.,Tokyo Institute of Technology
Journal of the Physical Society of Japan | Year: 2015

The valley Hall conductivity, having opposite signs between the K and K' valleys, is calculated in disordered monolayer graphene with gap. In ideal graphene without disorder, it is quantized into ±e2/2h within the gap and its absolute value decreases in proportion to the inverse of the Fermi energy in the band continuum. In the presence of scatterers, the Hall conductivity in the band continuum is strongly enhanced. This enhancement depends on explicit form of scattering potential even in the clean limit where the concentration and strength of scatterers are vanishingly small. Numerical calculations performed within the self-consistent Born approximation for scatterers with Gaussian potential and for charged impurities show that the valley Hall conductivity remains appreciable in the presence of large disorder and exhibits double-peak structure near zero energy. © 2015 The Physical Society of Japan.

Ando T.,Tokyo Institute of Technology
Journal of the Physical Society of Japan | Year: 2015

The valley Hall conductivity, having opposite signs between the K and KA valleys, is calculated in disordered bilayer graphene in the presence of gate electric field. Numerical calculations are performed within a self-consistent Born approximation for scatterers with Gaussian potential and for charged impurities. The results show that the valley Hall conductivity is much enhanced as compared to that in the ideal case without scatterers, remains appreciable in the presence of large disorder, and exhibits double-peak structure near zero energy. © 2015 The Physical Society of Japan.

Nasu J.,Tokyo Institute of Technology | Motome Y.,University of Tokyo
Physical Review Letters | Year: 2015

Thermodynamic properties of chiral spin liquids are investigated for a variant of the Kitaev model defined on a decorated honeycomb lattice. Using the quantum Monte Carlo simulation, we find that the model exhibits a finite-temperature phase transition associated with the time reversal symmetry breaking, in both topologically trivial and nontrivial regions. Numerical results for the Chern number and the thermal Hall conductivity indicate that the phase transition changes from a continuous to a discontinuous transition as we vary the coupling constants to reach the non-Abelian phase coming from the Abelian phase of the model. In addition, we find as a diagnostic of the chiral spin liquids, successive crossovers with multistage entropy release above the critical temperature, which indicates that the hierarchical fractionalization of a quantum spin occurs differently between the two regions. © 2015 American Physical Society. © 2015 American Physical Society.

Kawano Y.,Tokyo Institute of Technology
Journal of the Physical Society of Japan | Year: 2015

The terahertz (THz) research field is expected to serve as a new platform for studying low-energy excitation in solids and higher-order structures in large molecules, and for realizing applications in medicine, agriculture, security, and high-capacity communications. The THz frequency region, however, is located between the electronic and photonic bands, hampering the development of basic components like detectors and sources. This article presents an overview of basic background information about THz waves and THz detector applications and describes the THz response of carbon-based low-dimensional systems, such as single carbon nanotubes (CNT), CNT-array films, and graphene. © 2015 The Physical Society of Japan.

Iwai H.,Tokyo Institute of Technology
Solid-State Electronics | Year: 2015

Although Si MOS devices have dominated the integrated circuit applications over the four decades, it has been anticipated that the development of CMOS would reach its limits after the next decade because of the difficulties in the technologies for further downscaling and also because of some fundamental limits of MOSFETs. However, there have been no promising candidates yet, which can replace Si MOSFETs with better performance with low cost. Thus, for the moment, it seems that we have to stick to the Si MOSFET devices until their end. The downsizing is limited by the increase of off-leakage current between source and drain. In order to suppress the off-leakage current, multi-gate structures (FinFET, Tri-gate, and Si-nanowire MOSFETs) are replacing conventional planar MOSFETs, and continuous innovation of high-k/metal gate technologies has enabled EOT scaling down to 0.9 nm in production. However, it was found that the multi-gate structures have a future big problem of significant conduction reduction with decrease in fin width. Also it is not easy to further decrease EOT because of the mobility and reliability degradation. Furthermore, the development of EUV (Extremely Ultra-Violet) lithography, which is supposed to be essential for sub-10 nm lithography, delays significantly because of insufficient illumination intensity for production. Thus, it is now expected that the reduction rate of the gate length, which has a strong influence on the off-leakage current, will become slower in near future. © 2015 Elsevier Ltd.

Asano K.,Tokyo Institute of Technology | Meszros P.,Pennsylvania State University
Astrophysical Journal | Year: 2011

We present calculations of the time evolution of the prompt spectra of gamma-ray burst models involving generic internal dissipation regions, including internal shocks, either by itself or in the presence of an external photon source such as a photosphere. The method uses a newly developed time-dependent code involving synchrotron emission and absorption, inverse Compton scattering, and pair formation. The models reproduce the typically observed Band spectra and their generic time evolution, including the appearance of an extra keV-GeV component, whose delay in simple SSC models, however, is only partially able to explain the several seconds observed GeV delays. On the other hand, models involving both a photosphere and an internal dissipation region at a larger radius produce both an extra GeV component and time delays that are in the range of the observations. © 2011. The American Astronomical Society. All rights reserved.

Inoue S.,Tohoku University | Inoue S.,University College London | Saitoh T.R.,Tokyo Institute of Technology
Monthly Notices of the Royal Astronomical Society | Year: 2012

Bulges in spiral galaxies have been supposed to be classified into classical bulges or pseudo-bulges. Classical bulges are thought to form by galactic merger with bursty star formation, whereas pseudo-bulges are suggested to form by secular evolution due to spiral arms and a barred structure funnelling gas into the galactic centre. Noguchi suggested another bulge formation scenario, 'clump-origin bulge'. He demonstrated using a numerical simulation that a galactic disc suffers dynamical instability to form clumpy structures in the early stage of disc formation since the premature disc is expected to be highly gas rich, then the clumps are sucked into the galactic centre by dynamical friction and merge into a single bulge at the centre. This bulge formation scenario, which is expected to happen only at the high redshift, is different from the galactic merger and the secular evolution. Therefore, clump-origin bulges may have their own unique properties. We perform a high-resolution N-body/smoothed particle hydrodynamics simulation for the formation of the clump-origin bulge in an isolated galaxy model and study dynamical and chemical properties of the clump-origin bulge. We find that the clump-origin bulge resembles pseudo-bulges in dynamical properties, a nearly exponential surface density profile, a barred boxy shape and a significant rotation. We also find that this bulge consists of old and metal-rich stars, displaying resemblance to classical bulges. These natures, old metal-rich population but pseudo-bulge-like structures, mean that the clump-origin bulge cannot be simply classified into classical bulges or pseudo-bulges. From these results, we discuss similarities of the clump-origin bulge to the Milky Way bulge. Combined with a result of Elmegreen et al., this pseudo-bulge-like clump-origin bulge could be inferred to form in clump clusters with a relatively low surface density. © 2012 The Authors Monthly Notices of the Royal Astronomical Society © 2012 RAS.

Nakagawa S.,Tokyo Institute of Technology
Radiation Physics and Chemistry | Year: 2010

Methanol and 2-propanol solutions of hydroxymaleimide were irradiated with γ-ray and mechanism of its γ-irradiation-induced reactions was investigated through final-product analyses using high performance liquid chromatography (HPLC) coupled with mass spectroscopy. An addition reaction of a solvent radical toward hydroxymaleimide was dominant among its oxygen-free γ-irradiation-induced reactions in its alcohol solutions while it is known that electron attachment toward hydroxyphthalimide or hydroxysuccinimide is dominant among their γ-irradiation-induced reactions. The radical adduct abstracts hydrogen from solvent molecule to re-produce a solvent radical. Therefore, the degradation efficiency of hydroxymaleimide was more than ten times larger than that of hydroxyphthalimide and hydroxysuccinimide. Dimer was also produced through electron attachment process in the solutions of hydroxymaleimide. In addition, it was found that the degradation efficiency increased with decrease in dose rate. An additional reaction of a solvent radical toward hydroxymaleimide competes with a radical-radical recombination. The latter was reduced, with the former leading to efficient degradation of hydroxymaleimide increased by irradiation at lower dose rate. On the contrary, the production yield of the adduct radical as well as the degradation efficiency of hydroxymaleimide was inhibited in the presence of oxygen. © 2010 Elsevier Ltd. All rights reserved.

Maitani M.M.,Tokyo Institute of Technology | Allara D.L.,Pennsylvania State University
Topics in Current Chemistry | Year: 2012

Metal vapor deposition to form ohmic contacts is commonly used in the fabrication of organic electronic devices because of significant manufacturability advantages. In the case of single molecular layer devices, however, the extremely small thickness, typically ∼1-2 nm, presents serious challenges in achieving good contacts and device integrity. This review focuses on recent scientific aspects of metal vapor deposition on monolayer thickness molecular films, particularly self-assembled monolayers, ranging across mechanisms of metal nucleation, metal-molecular group interactions and chemical reactions, diffusion of metal atoms within and through organic films, and the correlations of these and other factors with device function. Results for both non-reactive and reactive metal deposition are reviewed. Finally, novel strategies are considered which show promise for providing highly reliable and durable metal/organic top contacts for use in metal-molecule-metal junctions for device applications. © 2011 Springer-Verlag Berlin Heidelberg.

Yamazaki K.,Tokyo Institute of Technology
Neurocomputing | Year: 2015

In semi-supervised classification, data are partially labeled and the task is to label the remaining data. Compared with unsupervised learning, it is expected that the labeling accuracy would be improved due to the information of the given labels. However, since the class labels are manually assigned by experts and data are sometimes difficult to collect, the assigned labels are noisy. Then, the balance of classes in the labeled data can be different from that in the unlabeled data. In order to solve this problem, a number of practical methods for modifying the class balance, such as instance re-weighting or re-sampling, have been proposed. Despite the increase in application studies, the effect of the noisy labels on the accuracy has not yet been thoroughly investigated. In the present paper, we theoretically analyze the accuracy of the semi-supervised classification. In comparison with the case of balanced classes, we observe the loss of accuracy caused by label noise. © 2015 Elsevier B.V.

Cai K.,Kings College | Ishii H.,Tokyo Institute of Technology
Automatica | Year: 2012

We study the average consensus problem of multi-agent systems for general network topologies with unidirectional information flow. We propose two linear distributed algorithms, deterministic and gossip, respectively for the cases where the inter-agent communication is synchronous and asynchronous. In both cases, the developed algorithms guarantee state averaging on arbitrary strongly connected digraphs; in particular, this graphical condition does not require that the network be balanced or symmetric, thereby extending previous results in the literature. The key novelty of our approach is to augment an additional variable for each agent, called "surplus", whose function is to locally record individual state updates. For convergence analysis, we employ graph-theoretic and nonnegative matrix tools, plus the eigenvalue perturbation theory playing a crucial role. © 2012 Elsevier Ltd. All rights reserved.

Priimagi A.,Aalto University | Priimagi A.,Polytechnic of Milan | Barrett C.J.,McGill University | Shishido A.,Tokyo Institute of Technology
Journal of Materials Chemistry C | Year: 2014

The design of functional and stimuli-responsive materials is among the key goals of modern materials science. The structure and properties of such materials can be controlled via various stimuli, among which light is often times the most attractive choice. Light is ubiquitous and a gentle energy source and its properties can be optimized for a specific target remotely, with high spatial and temporal resolution. Light-control over molecular alignment has in recent years attracted particular interest, for potential applications such as reconfigurable photonic elements and optical-to-mechanical energy conversion. Herein, we bring forward some recent examples and emerging trends in this exciting field of research, focusing on liquid crystals, liquid-crystalline polymers and photochromic organic crystals, which we believe serve to highlight the immense potential of light-responsive materials to a wide variety of current and future high-tech applications in photonics, energy harvesting and conversion. This journal is © the Partner Organisations 2014.

Ishijima S.,Tokyo Institute of Technology
PLoS ONE | Year: 2016

It is well established that the basis for flagellar and ciliary movements is ATP-dependent sliding between adjacent doublet microtubules. However, the mechanism for converting microtubule sliding into flagellar and ciliary movements has long remained unresolved. The author has developed new sperm models that use bull spermatozoa divested of their plasma membrane and midpiece mitochondrial sheath by Triton X-100 and dithiothreitol. These models enable the observation of both the oscillatory sliding movement of activated doublet microtubules and flagellar bend formation in the presence of ATP. A long fiber of doublet microtubules extruded by synchronous sliding of the sperm flagella and a short fiber of doublet microtubules extruded by metachronal sliding exhibited spontaneous oscillatory movements and constructed a one beat cycle of flagellar bending by alternately actuating. The small sliding displacement generated by metachronal sliding formed helical bends, whereas the large displacement by synchronous sliding formed planar bends. Therefore, the resultant waveform is a half-funnel shape, which is similar to ciliary movements. © 2016 Sumio Ishijima. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Ando T.,Tokyo Institute of Technology
Journal of Physics: Conference Series | Year: 2011

The conductivity is calculated for dominant charged-impurity scattering in graphenes within a self-consistent Born approximation. In monolayer graphene, environmental dielectric screening is shown to change their effective potential from short to long range. In bilayer graphene, effects of band-gap opening due to asymmetry between two layers caused by perpendicular electric field and effects of AA stacking are considered.

Maeda K.,Tokyo Institute of Technology | Maeda K.,Japan Science and Technology Agency
Catalysis Science and Technology | Year: 2014

The application of illuminated rutile TiO2 powder modified with a metal cocatalyst to the overall water splitting into H2 and O 2 was studied. Although unmodified rutile exhibited little activity, modification with a suitable amount of Pt nanoparticles resulted in observable H2 and O2 evolution from pure water under band-gap irradiation. Pt-loaded rutile TiO2 exhibited stable and high photocatalytic activity in pure water. The photocatalytic performance is much lower under acidic and basic conditions, due to a photo-corrosion effect and inefficient water reduction process, respectively. © The Royal Society of Chemistry 2014.

Nespolo M.,Tokyo Institute of Technology
Journal of Applied Crystallography | Year: 2015

A critical analysis of some basic notions often overlooked in crystallographic education is presented to correct some common oversights occurring both in the literature and in textbooks. The crystal forms (face forms), defined in terms of their geometric eigensymmetry, are 47 in number, not 48as often found in the literature. The split of the dihedron into dome and sphenoid calls for the consideration of the physical properties of the faces building a form; in that case, however, the same criterion should be used for all forms. By taking the handedness of the faces as representative of the physical properties of the faces, the occurrence of 128 crystallographic face forms (97 affine face forms and 31 enantiomorphic pairs) is demonstrated. Next, the correct use of non-coprime Miller indices when a centred unit cell is adopted is shown, and the inconsistent multiplication of Miller indices in the Bravais-Friedel-Donnay-Harker law is pointed out. A geometric derivation of the reflection conditions is reviewed. Finally, the inconsistent presentation of metric restrictions imposed by the structural symmetry is pointed out and corrected. © 2015 International Union of Crystallography.

Brasser R.,Tokyo Institute of Technology | Lee M.H.,University of Hong Kong
Astronomical Journal | Year: 2015

The migration and encounter histories of the giant planets in our solar system can be constrained by the obliquities of Jupiter and Saturn. We have performed secular simulations with imposed migration and N-body simulations with planetesimals to study the expected obliquity distribution of migrating planets with initial conditions resembling those of the smooth migration model, the resonant Nice model and two models with five giant planets initially in resonance (one compact and one loose configuration). For smooth migration, the secular spin-orbit resonance mechanism can tilt Saturn's spin axis to the current obliquity if the product of the migration timescale and the orbital inclinations is sufficiently large (exceeding 30 Myr deg). For the resonant Nice model with imposed migration, it is difficult to reproduce today's obliquity values, because the compactness of the initial system raises the frequency that tilts Saturn above the spin precession frequency of Jupiter, causing a Jupiter spin-orbit resonance crossing. Migration timescales sufficiently long to tilt Saturn generally suffice to tilt Jupiter more than is observed. The full N-body simulations tell a somewhat different story, with Jupiter generally being tilted as often as Saturn, but on average having a higher obliquity. The main obstacle is the final orbital spacing of the giant planets, coupled with the tail of Neptune's migration. The resonant Nice case is barely able to simultaneously reproduce the orbital and spin properties of the giant planets, with a probability The loose five planet model is unable to match all our constraints (probability <0.08%). The compact five planet model has the highest chance of matching the orbital and obliquity constraints simultaneously (probability ∼0.3%). © 2015. The American Astronomical Society. All rights reserved.

Kitadai N.,Tokyo Institute of Technology
Origins of Life and Evolution of Biospheres | Year: 2015

Alkaline hydrothermal systems have received considerable attention as candidates for the origin and evolution of life on the primitive Earth. Nevertheless, sufficient information has not yet been obtained for the thermodynamic properties of amino acids, which are necessary components for life, at high temperatures and alkaline pH. These properties were estimated using experimental high-temperature volume and heat capacity data reported in the literature for several amino acids, together with correlation algorithms and the revised Helgeson–Kirkham–Flowers (HKF) equations of state. This approach enabled determination of a complete set of the standard molal thermodynamic data and the revised HKF parameters for the 20 protein amino acids in their zwitterionic and ionization states. The obtained dataset was then used to evaluate the energetics of amino acid syntheses from simple inorganic precursors (CO2, H2, NH3 and H2S) in a simulated alkaline hydrothermal system on the Hadean Earth. Results show that mixing between CO2-rich seawater and the H2-rich hydrothermal fluid can produce energetically favorable conditions for amino acid syntheses, particularly in the lower-temperature region of such systems. Together with data related to the pH and temperature dependences of the energetics of amino acid polymerizations presented in earlier reports, these results suggest the following. Hadean alkaline hydrothermal settings, where steep pH and temperature gradients may have existed between cool, slightly acidic Hadean ocean water and hot, alkaline hydrothermal fluids at the vent–ocean interface, may be energetically the most suitable environment for the synthesis and polymerization of amino acids. © 2015, Springer Science+Business Media Dordrecht.

Tamaki T.,Tokyo Institute of Technology
Topics in Catalysis | Year: 2012

Enzymatic biofuel cells can use a variety of fuels such as glucose and ethanol, and they have the potential to power portable devices. This article summarizes recent advances made in the use of three-dimensional conducting materials as electrode matrices of enzymatic biofuel cells from the point of view of the current density and the power density. © Springer Science+Business Media New York 2012.

Motokawa T.,Tokyo Institute of Technology
Biological Bulletin | Year: 2011

Stiffness changes in response to mechanical and chemical stimulation were studied in muscle-free dermal samples from the body wall of the starfish Linckia laevigata. The ultrastructural study showed that the dermis was packed with collagen fibrils between which only a small number of cells were observed. Muscles were found only in the walls of coelomic extensions leading to papulae. Stress-strain tests were performed on isolated dermis containing no muscles. The tangent modulus was 27.5 MPa at 0.04% strain rate in the stress-strain tests. It was increased to 40.7 MPa by mechanical stimulation, which also increased the tensile strength and breaking-strain energy density. Dynamic mechanical tests showed that the increase in stiffness in response to mechanical stimulation was transient. Acetylcholine (10-6-10-3 mol l-1) and artificial seawater with an elevated potassium concentration (KASW) stiffened the dermis. Mechanical stimulation caused a 12% mass loss. KASW also caused mass loss, which was inhibited by anesthesia. These results clearly showed that the stiffness changes in the starfish dermis were based on a non-muscular mechanism that was similar to that of other echinoderm connective tissues with mechanical mutability. © 2011 Marine Biological Laboratory.

Nisisako T.,Tokyo Institute of Technology
Current Opinion in Colloid and Interface Science | Year: 2016

Microfluidic production of multicompartmental emulsion droplets and particles has received considerable attention of late. In particular, droplets having two physically and chemically distinct segments (so-called Janus droplets) and the anisotropic particles synthesized from these droplets, are becoming increasingly popular because of their novel and promising properties, which make them suitable for use in numerous applications, including for controlled drug release, display devices, and self-assembly. So far, a range of interesting anisotropies have been accorded to Janus droplets and particles via microfluidics; these span from chromatic, magnetic, and hydrophobic-hydrophilic characteristics to selective degradation properties. Here, we summarize and discuss the recent trends related to Janus droplets and particles produced through microfluidic processing. We also review the parallelization technologies being developed for scaling up microfluidic emulsification in the industry. © 2016 Elsevier Ltd.

Ohmori K.,Tokyo Institute of Technology
Chemical Record | Year: 2011

Flavan-derived polyphenols (catechin derivatives), widely destributed in the plant kingdom, have been given much considerable attention owing to their significant bioactivitites coupled with their extreme structural diversity. However, biochemical functions of this class of molecules are still not well understood because of the limited availavility of natural samples in sufficient quantity and quality. Here we report our synthetic challenges toward flavan-derived polyphenols, based on the flavonoid-sugar analogy. The key for success was the C(4)-elaboration of the flavan skeleton, which posed an important relevance to their structure diversification both in terms of the biogenetic origin of flavan derivatives as well as chemical synthesis of this class of compounds. Various nucleophilic units could be introduced to the C(4) position via the S N1-type substitution, and orthogonal activation of two distinct flavan units enabled block assembly of linear catechin oligomers. These methodologies would serve as a reliable way to supply valuable, homogeneuous samples for biological testing. © 2011 The Chemical Society of Japan and Wiley-VCH, Weinheim.

Yokoyama T.,Tokyo Institute of Technology | Alexander C.M.O.'.D.,Carnegie Institution of Washington | Walker R.J.,University of Maryland University College
Earth and Planetary Science Letters | Year: 2011

We report Os isotope compositions of acid residues separated from six carbonaceous chondrites that were subjected to varying degrees of aqueous alteration on their parent bodies. The residues from three enstatite chondrites were also investigated in order to evaluate the effects of nebular and parent body processing on the survival of presolar grains in meteorites formed under redox conditions that were markedly reduced, compared to those under which carbonaceous and ordinary chondrites formed. All acid residues from CM and CR chondrites show enrichments in s-process Os isotopes relative to the Solar System average recorded in bulk chondrites. The extent of the anomaly present positively correlates with the degree of aqueous alteration of the host chondrites. This correlation was probably caused by selective destruction/modification of presolar grains carrying r-process-enriched Os during progressive aqueous alteration on the parent bodies. The r-process-enriched component was likely either presolar silicates formed in Type II supernova ejecta, or other unidentified reduced presolar phases such as metal alloys, carbides and silicides. Acid residues from enstatite chondrites have Os isotope anomalies that are much more enriched in the s-process components, relative to the residues from carbonaceous and ordinary chondrites that experienced the same grade of thermal metamorphism. This most likely reflects the selective destruction of s-process-enriched presolar phases that occurred under the more oxidized conditions experienced by carbonaceous and ordinary chondrites, either while components formed in the nebula, or on their parent bodies. To account for the uniform, terrestrial Os isotopic composition in all types of bulk chondrites, it is required that r-process or s-process-enriched Os, released from presolar phases during nebular or parent body processing, was re-incorporated into a new phase(s) which was not lost from the location where the bulk meteorites were derived. However, because parent body processing might have acted differently on other elements (e.g., open system behavior of fluid mobile elements during aqueous alteration), recent findings of isotopic heterogeneities in bulk meteorites should be evaluated not just by invoking nebular heterogeneities, but by also considering the effects of parent body processing. © 2011 Elsevier B.V.

Kato Y.,Tokyo Institute of Technology
ISIJ International | Year: 2012

A new energy transformation concept based on carbon recycling, called the Active Carbon Recycling Energy System, ACRES, had been proposed for a zero carbon dioxide emission process. A smart ironmaking system based on ACRES (iACRES) was discussed thermodynamically. Efficient regeneration of carbon material from carbon dioxide (CO 2) emitted from ironmaking system was a key technology for establishment of iACRES. Carbon monoxide (CO) was the appropriate carbon material in recycling system of iACRES because CO had high enthalpy for reduction of iron oxide. CO regeneration by CO 2 hydrogenation was employed for carbon recycling because the regeneration was the most practical technology in regeneration ways. Equilibrium analysis for CO recycling in iACRES was discussed. Effluent gas of an iron making process is generally mixture of CO 2 and CO. Effect of concentration of CO 2 in gas for reduction on CO regeneration was discussed. CO 2 had small negative effect on CO reduction. Then, CO and CO 2 separation process for effluent gas from ironmaking process was capable to be omitted in iACRES. The omission of the process would realize simplification and cost-reduction of processes in iACRES. A structure of iACRES using external H 2 and high-temperature heat was proposed. It was shown that hydrogen was useful material as reductnat for CO 2 reduction in iACRES. © 2012 ISIJ.

Dobbs C.,University of Exeter | Baba J.,Tokyo Institute of Technology
Publications of the Astronomical Society of Australia | Year: 2014

The majority of astrophysics involves the study of spiral galaxies, and stars and planets within them, but how spiral arms in galaxies form and evolve is still a fundamental problem. Major progress in this field was made primarily in the 1960s, and early 1970s, but since then there has been no comprehensive update on the state of the field. In this review, we discuss the progress in theory, and in particular numerical calculations, which unlike in the 1960s and 1970s, are now commonplace, as well as recent observational developments. We set out the current status for different scenarios for spiral arm formation, the nature of the spiral arms they induce, and the consequences for gas dynamics and star formation in different types of spiral galaxies. We argue that, with the possible exception of barred galaxies, spiral arms are transient, recurrent and initiated by swing amplified instabilities in the disc. We suppose that unbarred m = 2 spiral patterns are induced by tidal interactions, and slowly wind up over time. However the mechanism for generating spiral structure does not appear to have significant consequences for star formation in galaxies. Copyright © 2014 Astronomical Society of Australia.

Natori K.,Tokyo Institute of Technology
IEEE Transactions on Electron Devices | Year: 2012

A compact model for the quasi-ballistic silicon nanowire MOSFET was developed by supplementing the ballistic framework previously disclosed by us with an original carrier-scattering model. The scattering model considers elastic scattering and optical phonon emission, which is the dominant route of energy relaxation in the device. The quasi-ballistic electric current showed a remarkable decrease compared with the ballistic counterpart. The relative decrease or "ballisticity" gradually improved when the channel length was reduced, but the value remained considerably less than the ballistic limit, even in the limit of zero channel length. The transport physics underlying the device characteristics is discussed. © 2006 IEEE.

Komabayashi T.,Carnegie Institution of Washington | Komabayashi T.,Tokyo Institute of Technology | Fei Y.,Carnegie Institution of Washington
Journal of Geophysical Research: Solid Earth | Year: 2010

An internally consistent thermodynamic database for pure iron has been established to pressures (P) up to 360 GPa and temperatures (T) up to 7000 K from existing static experimental data and thermochemical measurements. The database includes body-centered cubic (BCC) phases (a or d phase), the face-centered cubic (FCC) phase (g phase), the hexagonal close-packed (HCP) phase (e phase), and the liquid phase. We describe fundamental thermodynamic relations as the Gibbs free energy divided into thermochemical and thermophysical terms. The thermochemical data were evaluated from existing metallurgy databases together with experimentally determined phase relations. The thermophysical term is obtained from the pressure-volume-temperature equations of state (EoS) for the phases. We constructed an EoS of the FCC phase from our recent internally-heated diamond anvil cell (DAC) experimental data and assessed the EoS of the liquid phase from existing laser-heated DAC experiments together with density data at P = 1 bar, 0.2 GPa, and along the Hugoniot. The HCP-FCC-liquid triple point is located at P = 90 GPa and T= 2800 K. The calculated melting temperature of HCP iron at the inner core boundary (P = 330 GPa) is 4900 K and the density change at melting is -1.2%. The core density deficits at the inner core boundary are 8.1 wt.% and 5.3 wt.% for the liquid outer core and solid inner core, respectively. The calculated melting temperature is much lower than that from dynamic shock wave experiments, suggesting that the HCP structure may not be stable in the inner core. We included a hypothetical high-pressure BCC phase which could be stabilized above 220 GPa by a solid-solid transition of high-P BCC-HCP phases. This hypothetical BCC phase should have a large entropy to give a high melting temperature in order to reconcile the existing discrepancies between the static and shock wave experimental studies. © Copyright 2010 by the American Geophysical Union.

Houser C.,Tokyo Institute of Technology
Earth and Planetary Science Letters | Year: 2016

Knowledge of the Earth's present water content is necessary to constrain the amount of water and other volatiles the Earth acquired during its formation and the amount that is cycled back into the interior from the surface. This study compares 410 and 660 km discontinuity depth with shear wave tomography within the mantle transition zone to identify regions with seismic signals consistent with water. The depth of the 410 and 660 km discontinuities is determined from a large updated dataset of SS-S410S and SS-S660S differential travel times, known as SS precursors. The discontinuity depths measured from binning and stacking the SS precursor data are then compared to the shear velocity model HMSL-S06 in the transition zone. Mapping all the possible combinations, very few locations match the predictions from mineral physics for the effects of water on discontinuity depth and shear velocity. The predictions, although not yet measured at actual transition zone temperatures and pressures, are a shallow 410 km discontinuity, a deep 660 km discontinuity, and a slow shear velocity. Only 8% of the bins with high-quality data are consistent with these predictions, and the calculated average water content within these bins is around 0.6 wt.%. A few isolated locations have patterns of velocity/topography that are consistent with water, while there are large regional-scale patterns consistent with cold/hot temperature anomalies. Combining this global analysis of long period seismic data and the current mineral physics predictions for water in transition zone minerals, I find that the mantle transition zone is generally dry, containing less than one Earth ocean of water. Although subduction zones could be locally hydrated, the combined discontinuity and velocity data show no evidence that wadsleyite or ringwoodite have been globally hydrated by subduction or initial Earth conditions. © 2016 Elsevier B.V.

Takagi H.,Tokyo Institute of Technology | Bricker J.D.,Tohoku University
Coastal Engineering Journal | Year: 2014

The 2011 Great East Japan Earthquake and Tsunami caused devastation all along the coast of eastern Japan. Ishinomaki City was one of the most severely damaged municipalities, though the height of the tsunami in this city was smaller than that in Iwate and northern Miyagi. A large difference in the extent of building damage was found comparing two areas of Ishinomaki: one not protected by breakwaters, and the other behind the breakwaters of a large Fishery port. In this paper, the authors perform numerical simulations to determine whether these general breakwaters, which were designed not to block tsunamis but wind waves, reduced the tsunami's energy and contributed to a reduction in inundation of the areas behind the port. Before assessing the effectiveness of breakwaters against tsunamis, simulated inundation heights in each of these two areas were compared with heights measured by The 2011 Tohoku Earthquake Tsunami Joint Survey Group. It was found that a simulation with larger Manning's n value (n = 0.30) can evaluate inundation more precisely than when this value is small (n = 0.06), as often used by Japanese coastal engineers. Comparing the region protected by breakwaters with the unsheltered area, the results of a 2D shallow water equation model do not show a significant difference in inundation mainly because the tsunami intrudes through the openings in the breakwater and fills up the port basin with seawater in a very short time. Therefore, the effectiveness of general breakwaters in reducing tsunami impact should not be overestimated. However, a hypothetical study shows that water levels could be greatly reduced if the port were fully enclosed by breakwaters. This implies that a port could substantially reduce tsunami inundation if the breakwater openings were equipped to be closed before tsunami arrival. The authors also demonstrate that the difference in the extent of building damage in the two areas of Ishinomaki considered can be explained by the difference in drag forces due to the topography as well as the difference in land use, rather than by the presence of breakwaters. © 2014 World Scientific Publishing Company and Japan Society of Civil Engineers.

Todoroki A.,Tokyo Institute of Technology
Advanced Composite Materials | Year: 2012

When an alternating current is applied to a conductive slab, the induced current impedes the electric current and causes a skin effect. This effect is found in all conductive materials. For laminated carbon fiber reinforced plastics (CFRP), however, the depth of the skin effect has not previously been evaluated. In the present study, therefore, we analytically solve Maxwell's equations to derive the skin effect depth of unidirectional CFRP. Using this result, the skin effect is analyzed for laminated CFRP, and its depth is then derived. The effect is then compared with a newly defined skin effect of anisotropic conductance. For highly toughened CFRP that have resin rich layers, the skin effect of anisotropic conductance is found to be more important than that of the alternating current. © 2012 Japan Society for Composite Materials, Korean Society for Composite Materials and Taylor & Francis.

Ahmed R.,University of Bristol | Priimagi A.,Aalto University | Priimagi A.,Tokyo Institute of Technology | Faul C.F.J.,University of Bristol | Manners I.,University of Bristol
Advanced Materials | Year: 2012

Organometallic Gratings: The ionic self-assembly of metal-containing block-copolymer polyelectrolytes and azobenzene chromophores is exploited for the efficient production of stable photo-induced surface-relief gratings. We show that feature sizes can be tuned using simple redox chemistry, and that the chromophores can be removed during plasma treatment to yield ceramic-based optical materials. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Hu J.,Tokyo Institute of Technology
Biotechnology progress | Year: 2010

A simple two-chamber diffusion method was developed to study the diffusion properties of bacteriophages (phages). The apparent diffusion coefficients (D(app)) of Myoviridae phage T4 and filamentous phage fNEL were investigated, and the diffusion of the phages was found to be much slower than the diffusion of three antibiotics, ciprofloxacin, penicillin G, and tetracycline. D(app) of T4 and fNEL in water through filter paper were calculated to be 2.8 x 1011 m2/s and 6.8 x 1012 m2/s, respectively, and D(app) of fNEL through agarose gel membrane, an artificial biofilm, was also calculated to be smaller than that of T4. In addition, D(app) of phages through agarose gel was dependent on agarose concentration due to the similar size of phage and agarose gel mesh. We concluded that D(app) of phages through an artificial biofilm is dependent on both phage morphology and biofilm density, and suggest the use of this method to study diffusion properties through real biofilms. © 2010 American Institute of Chemical Engineers

Whitington T.,University of Queensland | Frith M.C.,Tokyo Institute of Technology | Johnson J.,University of Queensland | Bailey T.L.,University of Queensland
Nucleic Acids Research | Year: 2011

Chromatin immunoprecipitation followed by highthroughput sequencing (ChIP-seq) allows researchers to determine the genome-wide binding locations of individual transcription factors (TFs) at high resolution. This information can be interrogated to study various aspects of TF behaviour, including the mechanisms that control TF binding. Physical interaction between TFs comprises one important aspect of TF binding in eukaryotes, mediating tissue-specific gene expression. We have developed an algorithm, spaced motif analysis (SpaMo), which is able to infer physical interactions between the given TF and TFs bound at neighbouring sites at the DNA interface. The algorithm predicts TF interactions in half of the ChIP-seq data sets we test, with the majority of these predictions supported by direct evidence from the literature or evidence of homodimerization. High resolution motif spacing information obtained by this method can facilitate an improved understanding of individual TF complex structures. SpaMo can assist researchers in extracting maximum information relating to binding mechanisms from their TF ChIP-seq data. SpaMo is available for download and interactive use as part of the MEME Suite (http://meme.nbcr. net). © 2011 The Author(s).

Sanghamitra N.J.M.,Kyoto University | Ueno T.,Kyoto University | Ueno T.,Tokyo Institute of Technology
Chemical Communications | Year: 2013

Bioinorganic chemistry is of growing importance in the fields of nanomaterial science and biotechnology. Coordination of metals by biological systems is a crucial step in intricate enzymatic reactions such as photosynthesis, nitrogen fixation and biomineralization. Although such systems employ protein assemblies as molecular scaffolds, the important roles of protein assemblies in coordination chemistry have not been systematically investigated and characterized. Many researchers are joining the field of bioinorganic chemistry to investigate the inorganic chemistry of protein assemblies. This area is emerging as an important next-generation research field in bioinorganic chemistry. This article reviews recent progress in rational design of protein assemblies in coordination chemistry for integration of catalytic reactions using metal complexes, preparation of mineral biomimetics, and mechanistic investigations of biomineralization processes with protein assemblies. The unique chemical properties of protein assemblies in the form of cages, tubes, and crystals are described in this review. © 2013 The Royal Society of Chemistry.

Yasui S.,Tokyo Institute of Technology
Physical Review C - Nuclear Physics | Year: 2016

The Kondo effect for isospin-exchange interaction between a D, B meson and a valence nucleon in charm and bottom atomic nuclei including the discrete energy levels for valence nucleons is discussed. To investigate the binding energy by the Kondo effect, I introduce the mean-field approach for the bound state of the D, B meson in charm and bottom nuclei. Assuming a simple model, I examine the validity of the mean-field approximation by comparing the results with the exact solutions. The effect of the quantum fluctuation is estimated beyond the mean-field approximation. The competition between the Kondo effect and the other correlations in valence nucleons, the isospin symmetry breaking and the nucleon pairings, are discussed. © 2016 American Physical Society.

Todoroki A.,Tokyo Institute of Technology
Transactions of the Japan Society for Aeronautical and Space Sciences | Year: 2012

This paper deals with a new lamination theory to calculate the electric current density on carbon fiber reinforced plastic (CFRP) laminates. Unidirectional CFRP has strong orthotropic electric conductance. When electric current is applied to the surface of a CFRP plate, the electric voltage field is not uniform in the thickness direction for thick CFRP. The electric current concentrates near the surface where the electric current is applied to thick CFRP laminates. In this study, a new lamination theory for thick CFRP laminates is proposed. The theory for thick CFRP assumes a non-uniform electric voltage distribution in the thickness direction. For non-thick and non-thin CFRP plates, an approximation method is proposed. To obtain the shape of the non-uniform voltage distribution, the analytical results of thick unidirectional ply from a previous paper is adopted as a contribution function to calculate the effective conductance of the thick CFRP laminate. Cross-sectional two-dimensional (2D) FEM analysis is used to obtain the contribution function for the nonthick CFRP plate. The proposed methods are applied to two cases of the thick CFRP plates, and the results are compared with the three-dimensional (3D) FEM results. Consequently, the new lamination theory is shown to be very effective for the CFRP plates. © 2012 The Japan Society for Aeronautical and Space Sciences.

Goto H.,Kyoto University | Morikawa H.,Tokyo Institute of Technology
Soils and Foundations | Year: 2012

The 2011 off the Pacific Coast of Tohoku Earthquake (MW 9:0) caused severe damage not only because of the great tsunami, but also because of the ground motions. In the present paper, we report some details of the source mechanism and the ground motions during the earthquake, and discuss the ground motion characteristics related to the damage in the Tsukidate and Furukawa areas. Damage grades in Tsukidate, where the largest peak ground accelerations were observed, are not severe in comparison to those in Furukawa. The pseudo-velocity response spectrum for the ground motions observed in the Furukawa area is similar to that in the JR Takatori records for the 1995 Kobe earthquake. © 2012 The Japanese Geotechnical Society.

Cai K.,Kings College | Ishii H.,Tokyo Institute of Technology
Automatica | Year: 2012

We have recently proposed quantized gossip algorithms which solve the consensus and averaging problems on directed graphs with the least restrictive connectivity requirements. In this paper we study the convergence time of these algorithms. To this end, we investigate the shrinking time of the smallest interval that contains all states for the consensus algorithm, and the decay time of a suitable Lyapunov function for the averaging algorithm. The investigation leads us to characterize the convergence time by the hitting time in certain special Markov chains. We simplify the structures of state transition by considering the special case of complete graphs, where every edge can be activated with an equal probability, and derive polynomial upper bounds on convergence time. © 2012 Elsevier Ltd. All rights reserved.

Murakami S.,Tokyo Institute of Technology
New Journal of Physics | Year: 2011

Topological insulators (quantum spin Hall systems) are insulating in the bulk but have gapless edge/surface states, which remain gapless even when nonmagnetic disorder or interaction is present. This robustness stems from the topological nature characterized by the Z2 topological number, and this offers us various kinds of new novel properties. We review prominent advances in theories and in experiments on topological insulators since their theoretical proposal in 2005. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.

Wu P.,East China Normal University | Kubota Y.,Yokohama National University | Yokoi T.,Tokyo Institute of Technology
ACS Catalysis | Year: 2014

On the occasion of Professor Takashi Tatsumi's retirement and winning of the Alwin Mittasch Prize, some of his main achievements in zeolite catalysis are summarized, with a focus on the design, synthesis, and catalytic application of new titanosilicate catalysts. He and his co-workers succeeded in the direct synthesis of the MWW-type titanosilicate, Ti-MWW, by employing boric acid in the synthesis and thereafter developed a dry gel conversion method for boron-reduced Ti-MWW as well as a secondary isomorphous substitution route for boron-free Ti-MWW molecular sieves. In particular, the postsynthetic conversion involved a reversible structure interchange between three-dimensional silicalite and a two-dimensional layered precursor. Taking advantage of the structural diversity of the layered MWW zeolite precursor, phase-delaminated Ti-MMW and interlayer expanded Ti-MWW were also prepared. Using hydrogen peroxide as an oxidant, the Ti-MWW/H2O2 system was highly efficient for liquid-phase oxidation of a variety of substrates, particularly the epoxidation of alkenes and ammoximation of ketones. Some of the Ti-MWW-catalyzed reactions have already led to or are becoming practical catalytic technologies in industrial practice. Several other recent achievements in the synthesis and catalytic applications of other titanosilicates, zeolitic hydrid materials, and solid acid zeolite catalysts are also briefly summarized. © 2013 American Chemical Society.

McCann E.,Lancaster University | Koshino M.,Tokyo Institute of Technology
Physical Review B - Condensed Matter and Materials Physics | Year: 2010

Since the lattices of ABA -stacked graphene multilayers with an even number of layers, as well as that of monolayer graphene, satisfy spatial-inversion symmetry, their electronic bands must be spin degenerate in the presence of time-inversion symmetry. In intrinsic monolayer and bilayer graphene, when symmetry is not broken by external fields, the only spin-orbit coupling present at low energy near the corner of the Brillouin zone is the Kane-Mele term, that opens a bulk energy gap but does not break the spin degeneracy of the energy bands. However, spin splitting is allowed in multilayers with an odd number of layers (≥3) because their lattices do not satisfy spatial-inversion symmetry. We show that, in trilayer graphene, in addition to the Kane-Mele term, there is a second type of intrinsic spin-orbit coupling present at low energy near the corner of the Brillouin zone. It introduces a Zeeman-type spin splitting of the energy bands at each valley with an opposite sign of the effective magnetic field in the two valleys. We estimate the magnitude of the effective field to be ∼2T. © 2010 The American Physical Society.

Koshino M.,Tokyo Institute of Technology | McCann E.,Lancaster University
Physical Review B - Condensed Matter and Materials Physics | Year: 2010

We study spatial symmetry in general ABA -stacked multilayer graphene to illustrate how electronic spectra at the two valleys are related in a magnetic field. We show that the lattice of multilayers with an even number of layers as well as that of monolayer graphene satisfy spatial inversion symmetry, which rigorously guarantees valley degeneracy in the absence of time-reversal symmetry. A multilayer with an odd number of layers (three or more) lacks inversion symmetry, but there is another transformation imposing an approximate valley degeneracy, which arises because the low-energy Hamiltonian consists of separate monolayerlike and bilayerlike parts. We show that an external electrostatic potential generally breaks valley degeneracy in a magnetic field, in a markedly different manner in odd and even multilayers. © 2010 The American Physical Society.

Todoroki A.,Tokyo Institute of Technology
Transactions of the Japan Society for Aeronautical and Space Sciences | Year: 2012

A new analytical method to calculate the electric current density between two probes in carbon-fiber-reinforced plastic (CFRP) is presented. Unidirectional CFRP has strongly orthotropic electric conductance. Even when electric current is applied to a CFRP plate using two probes on a single surface, the electric current density is not uniform along the cross-section. The electric current is concentrated near the surface where an electric current is applied. Although it is important to know the electric current density in the CFRP plate for the analysis of lightning effects, the density is difficult to calculate using a three-dimensional finite element model. In the present study, the orthotropic coordinate is transformed into a uniform coordinate. Laplace's equation is solved using the potential theory for a perfect fluid. Equations solved employing an infinite-body approximation are verified with a finite element model. As a result, the new analysis method is demonstrated to be efficient for unidirectional CFRP. The limitations of the method are also discussed. © 2012 The Japan Society for Aeronautical and Space Sciences.

Kawai K.,Tokyo Institute of Technology | Tsuchiya T.,Ehime University
Journal of Geophysical Research: Solid Earth | Year: 2012

In order to understand the fate of subducted continental materials by means of mechanisms such as tectonic erosion and sediment subduction, it is important to understand the high-pressure stability and elastic properties of grossular garnet. We study these questions using the first principles computation method. Grossular garnet was found to dissociate into an assemblage of CaSiO3 Ca-perovskite (Pv) and Al2O3 corundum (Cor) at about 23.4 GPa, accompanied by remarkable jumps of compressional wave (8.0%), shear wave (11.6%), bulk sound (5.7%) velocities, and density (12.1%). Although Pv with the grossular garnet composition was suggested experimentally after the decomposition reaction, this phase was found to be less stable than an assemblage of CaPv and Cor at pressures higher than 20 GPa. This indicates that observed Pv with the grossular garnet composition is metastable but can be obtained because of the slow kinetics of the garnet decomposition reaction. Our results imply that the dissociation of grossular garnet (as well as that of jadeite) included in continental materials subducted into the deep mantle increases the complexity of the 660 km discontinuity and can explain seismically observed multiple reflections. We have also investigated the anisotropy of elastic velocities of grossular garnet, CaPv, and Cor and found that CaPv is the most anisotropic mineral. This implies that CaPv could produce seismic anisotropy in the uppermost lower mantle. © 2012 by the American Geophysical Union.

Yoshida N.,Tokyo Institute of Technology | Takahashi Y.,Hiroshima University
Elements | Year: 2012

Radionuclides, such as 134Cs, 137Cs, and 131I, were released during the Fukushima Daiichi nuclear power plant accident in March 2011. Their distribution was monitored by airborne surveys and soil sampling. The most highly contaminated areas are to the northwest of the plant and in the Naka-dori region of Fukushima Prefecture; this contamination was mainly the result of wet deposition on March 15. Radionuclides were also released on March 21, and they were dispersed up to 200 km south of the plant. The Cs/I ratios are different for these two events, probably because of differences in the initial ratios in the airborne plumes and the amount of wet deposition. Numerical simulations of the dispersion process and vertical profiles of radionuclides in soils are used to describe the contamination of soils.

Kawai K.,Tokyo Institute of Technology | Tsuchiya T.,Ehime University
American Mineralogist | Year: 2012

New hexagonal aluminous (NAL) phase and orthorhombic calcium-ferrite (CF) type phase are considered to be major mantle components of the mid-ocean ridge basalt (MORB) at pressure and temperature conditions in the lower mantle, which can potentially host alkali elements with large ionic radii. The high-pressure stability and elastic properties of both NAL and CF phases are therefore of fundamental importance for understanding the fate of subducted MORB. Here we report those properties of the NaMg 2Al 5SiO 12 system studied by means of the first-principles computation method. NAL was found to transform to the CF phase at 39.6 GPa, accompanied by discontinuities in density (+1.8%), as well as compressional wave (-0.2%), shear wave (+0.9%), and bulk sound (-1.0%) velocities. The property of subducted MORB was evaluated using these results, and the velocity contrast between pyrolite and MORB of ~ -5% was found to be quite comparable to the shear velocity anomaly observed for seismic scatterers at depths from 1100 to 1800 km. However, since the transformation of the NAL to CF phase within MORB produces insignificant increases in the seismic velocities, it would be seismologically undetectable. On the other hand, the anisotropy change associated with the phase transition is significant and could be seismically detectable using observations such as shear wave splitting measurements since the CF phase is considerably more anisotropic compared to the NAL phase.

Jespersen T.S.,Copenhagen University | Grove-Rasmussen K.,Copenhagen University | Grove-Rasmussen K.,Nippon Telegraph and Telephone | Paaske J.,Copenhagen University | And 4 more authors.
Nature Physics | Year: 2011

Understanding how the orbital motion of electrons is coupled to the spin degree of freedom in nanoscale systems is central for applications in spin-based electronics and quantum computation. Here we demonstrate such sping-orbit coupling in a carbon-nanotube quantum dot in the general multielectron regime and in the presence of finite disorder. Also, we find a systematic dependence of the sping-orbit coupling on the electron occupation of the quantum dot. Such a dependence has not been seen in any other system and follows from the curvature-induced sping-orbit-split Dirac spectrum of the underlying graphene lattice. Our findings suggest that the sping-orbit coupling is a general property of carbon-nanotube quantum dots, which should provide a unique platform for the study of sping-orbit effects and their applications. © 2011 Macmillan Publishers Limited. All rights reserved.

Enoki T.,Tokyo Institute of Technology
Physica Scripta T | Year: 2012

In graphene edges or nanographene, the presence of edges strongly affects the electronic structure depending on their edge shape (zigzag and armchair edges) as observed with the electron wave interference and the creation of non-bonding π-electron state (edge state). We investigate the edge-inherent electronic features and the magnetic properties of edge-sate spins in nanographene/graphene edges. Graphene nanostructures are fabricated by heat-induced conversion/fabrication of nanodiamond particles/graphite step edges; single-layer nanographene islands (mean size 10 nm) and armchair-edged nanographene ribbons (width 8 nm). Scanning tunneling microscopy (STM)/scanning tunneling spectroscopy observations demonstrate that edge states are created in zigzag edges in spite of the absence of such states in armchair edges. In addition, zigzag edges tend to be short and defective, whereas armchair edges are long and continuous in general. These findings suggest that a zigzag edge has lower aromatic stability than an armchair edge, consistent with Clar's aromatic sextet rule. The manner in which electron wave scattering takes place is different between zigzag and armchair edges. In the vicinity of an armchair edge, a honeycomb superlattice is observed in STM images together with a fine structure of threefold symmetry, in spite of the (√3×√3) R30° superlattice at a zigzag edge. The honeycomb lattice is a consequence of the intervalley K-K' transition that accompanies the electron wave interference taking place at the armchair edge. The Raman G-band is also affected by the interference, showing polarization angle dependence specifically at armchair edges. The magnetism of a three-dimensional disordered network of nanographene sheets is understood on the basis of the ferrimagnetic structure of the edge-state spins in individual constituent nanographene sheets. The strengthening of the inter-nanographene-sheet magnetic interaction brings about a spin glass state. © 2012 The Royal Swedish Academy of Sciences.

Wakai F.,Tokyo Institute of Technology | Brakke K.A.,Susquehanna University
Acta Materialia | Year: 2011

Sintering by coupled grain boundary and surface diffusion was analyzed in terms of mechanics. The shrinkage is a result of the relative motion of particles caused by grain boundary diffusion. The center of mass of a particle also moves due to spheroidization of the particles by surface diffusion. The mobility and sintering force for both processes were calculated during sintering of two identical particles until they reached equilibrium. The contribution of grain boundary diffusion to the final shrinkage increased with increasing ratio of grain boundary diffusion coefficient to surface diffusion coefficient and the ratio of grain boundary energy to surface energy. © 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Yu H.,Nagaoka University of Technology | Ikeda T.,Tokyo Institute of Technology
Advanced Materials | Year: 2011

Coupling photochromic molecules with liquid crystalline (LC) materials enables one to reversibly photocontrol unique LC features such as phase transition, photoalignment, and molecular cooperative motion. LC elastomers show photomechanical and photomobile properties, directly converting light energy into mechanical energy. In well-defined LC block copolymers, regular patternings of nanostructures in macroscopic scales are fabricated by photo-manipulation of LC actuators. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Wakai F.,Tokyo Institute of Technology | Nikolic Z.S.,University of Nis
Acta Materialia | Year: 2011

Macroscopic quantities such as strain rate and viscosity during sintering can be obtained from the microscopic motion of particles normal and tangential to grain boundaries. When grain boundary diffusion is the dominant transport mechanism of sintering, the viscous shear modulus and viscous Poisson's ratios are dependent on the grain boundary diffusion coefficient and the microscopic viscosity of grain boundary sliding. The microscopic viscosity is not constant, varying with microstructural evolution during sintering. The viscous Poisson's ratio decreases with increasing microscopic viscosity, and increases with relative density. The viscous Poisson's ratio for a given relative density is also dependent on the local configuration and the ratio of grain boundary energy to surface energy. © 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Nakatogawa H.,Tokyo Institute of Technology
Autophagy | Year: 2015

As with the case of the mechanism of autophagosome formation, studies in yeast have taken a leading role in elucidating the molecular basis of target recognition during selective autophagy. Degradation targets are recognized by receptor proteins, which also bind to Atg8 homologs on growing phagophore membranes, leading to the loading of the targets into autophagosomes. However, it remains to be elucidated how these processes are regulated. In yeast, receptors also interact with the scaffold/adaptor protein Atg11, which subsequently recruits core Atg proteins onto receptor-target complexes to initiate autophagosome formation. Recently, we found that Hrr25, a homolog of CSNK1D/casein kinase 1δ, regulates 3 of 4 selective autophagy-related pathways in the budding yeast Saccharomyces cerevisiae by a uniform mechanism: phosphoregulation of the receptor-scaffold interaction. © 2015 Taylor & Francis Group, LLC.

Taguchi H.,Tokyo Institute of Technology
Journal of Molecular Biology | Year: 2015

Chaperonin GroEL is an essential chaperone that assists in protein folding in the cell. Since one GroEL ring binds one GroES heptamer, the GroEL double ring permits the formation of two types of GroEL:GroES complexes: asymmetric 1:1 "bullet"-shaped and symmetric 1:2 "football"-shaped GroEL:GroES2 complexes. There have been continuing debates about the mechanism and which complex is critical to the chaperonin-assisted folding. In this review, I summarize the recent progress on the football complex. © 2015 Elsevier Ltd.All rights reserved.

Michinobu T.,Tokyo Institute of Technology | Michinobu T.,Japan Science and Technology Agency
Pure and Applied Chemistry | Year: 2010

A high-yielding addition reaction between electron-rich alkynes and a small acceptor molecule, tetracyanoethylene (TCNE), was employed as a new click reaction to construct donor-acceptor chromophores in the polymer main chains and side chains. The donor-acceptor alternating conjugated polymers were prepared from the ferrocenecontaining poly(aryleneethynylene)s in one step and atom-economic fashion. The energy levels and thermal properties of the aromatic polyamines substituted by electron-rich alkynes as a side chain can be tunable by the amount of the added TCNE. The resulting donor-acceptor-type polymers feature broad charge-transfer (CT) bands in the visible region, potent redox activities, and improved thermal properties. © 2010 IUPAC.

Ida S.,Tokyo Institute of Technology | Lin D.N.C.,University of California at Santa Cruz | Lin D.N.C.,Peking University
Astrophysical Journal | Year: 2010

Radial velocity and transit surveys indicate that solar-type stars bear super-Earths, with masses up to ∼20M⊕ and periods up to a few months, that are more common than those with Jupiter-mass gas giants. In many cases, these super-Earths are members of multiple-planet systems in which their mutual dynamical interaction has influenced their formation and evolution. In this paper, we modify an existing numerical population synthesis scheme to take into account protoplanetary embryos' interaction with their evolving natal gaseous disks, as well as their close scatterings and resonant interaction with each other. We show that it is possible for a group of compact embryos to emerge interior to the ice line, grow, migrate, and congregate into closely packed convoys which stall in the proximity of their host stars. After the disk-gas depletion, they undergo orbit crossing, close scattering, and giant impacts to form multiple rocky Earths or super-Earths in non-resonant orbits around ∼0.1 AU with moderate eccentricities of ∼0.01-0.1. We suggest that most refractory super-Earths with periods in the range of a few days to weeks may have formed through this process. These super-Earths differ from Neptune-like ice giants by their compact sizes and lack of a substantial gaseous envelope. © 2010. The American Astronomical Society. All rights reserved.

Tamaura Y.,Tokyo Institute of Technology
Ambio | Year: 2012

When a concentrated solar beam is irradiated to the ceramics such as Ni-ferrite, the high-energy flux in the range of 1500-2500 kW/m2 is absorbed by an excess Frenkel defect formation. This non-equilibrium state defect is generated not by heating at a low heating-rate (30 K/min), but by irradiating high flux energy of concentrated solar beam rapidly at a high heating rate (200 K/min). The defect can be spontaneously converted to chemical energy of a cation-excess spinel structure (reduced-oxide form) at the temperature around 1773 K. Thus, the O2 releasing reaction (α-O2 releasing reaction) proceeds in two-steps; (1) high flux energy of concentrated solar beam absorption by formation of the non-equilibriumFrenkel defect and (2) the O2 gas formation from the O2- in the Frenkel defect even in air atmosphere. The 2nd step proceeds without the solar radiation. We may say that the 1st step is light reaction, and 2nd step, dark reaction, just like in photosynthesis process. © Royal Swedish Academy of Sciences 2012.

Kato Y.,Tokyo Institute of Technology
Nuclear Engineering and Design | Year: 2014

A new energy transformation concept based on carbon recycling, called as active carbon recycling energy system, ACRES, was proposed for a zero carbon dioxide emission process. The ACRES is driven availably by carbon dioxide free primary energy. High temperature gas cooled reactor (HTGR) is a candidate of the energy sources for ACRES. A smart ironmaking system with ACRES (iACRES) is one of application examples. The contribution of HTGR on iACRES was discussed thermodynamically in this study. A carbon material is re-used cyclically as energy carrier media in ACRES. Carbon monoxide (CO) had higher energy densities than hydrogen and was compatible with conventional process. Thus, CO was suitable recycling media for ACRES. Efficient regeneration of CO was a key technology for ACRES. A combined system of hydrogen production by water electrolysis and CO2 hydrogen reduction was candidate. CO2 direct electrolysis was also one of the candidates. HTGR was appropriate heat source for both water and CO2 electrolysises, and CO2 hydrogen reduction. Thermodynamic energy balances were calculated for both systems with HTGR for an ironmaking system. The direct system showed relatively advantage to the combined system in the stand point of enthalpy efficiency and simplicity of the process. One or two plants of HTGR are corresponding with ACRES system for one unit of conventional blast furnace. The proposed ACRES system with HTGR was expected to form the basis of a new energy industrial process that had low CO2 emission. © 2013 Elsevier B.V.

Miyamoto Y.,National Health Research Institute | Yamauchi J.,National Health Research Institute | Yamauchi J.,Tokyo Institute of Technology
Cellular Signalling | Year: 2010

Dock180-related proteins are genetically conserved from Drosophila and C. elegans to mammals and are atypical types of guanine-nucleotide exchange factors (GEFs) for Rac and/or Cdc42 of small GTPases of the Rho family. Eleven members of the family occur in mammalian cells, each playing key roles in many aspects of essential cellular functions such as regulation of cytoskeletal organization, phagocytosis, cell migration, polarity formation, and differentiation. This review will summarize the newly accumulated findings concerning the Dock180-related proteins' molecular and cellular functions, emphasizing the roles of these proteins in neuronal cells and glial cells as well as their interactions in the central and peripheral nervous systems. © 2009 Elsevier Inc. All rights reserved.

Tsuchiya J.,Ehime University | Tsuchiya J.,Tokyo Institute of Technology
American Mineralogist | Year: 2013

Lizardite, being one of three serpentine minerals is of considerable interest in connection with understanding the geological processes occurring at subduction zones where serpentinized ocean floor is recycled into the Earth's mantle. The crystal structure, elasticity, and vibrational properties of lizardite under pressure were determined using first-principles techniques. Above 10 GPa, a stable and a metastable structures were obtained. The hydrogen bond geometry of the stable structure indicates the disappearance of hydrogen bonds above 10 GPa, whereas the metastable structure does not show any noticeable change of the hydrogen bond strength throughout the pressure range up to 20 GPa. At 10 GPa, a very sudden softening of the elastic constants was observed for the stable structure, which is associated with a slight change in the compressibility of the c axis. This elastic softening causes a sudden reduction in the seismic velocities νP and νφ by about 16 and 24%, respectively. These velocities then steeply increase with further compression. Shear velocity νS, on the other hand, gradually decreases with pressure and then abruptly increases about 14% at 10 GPa. The calculated OH stretching frequencies also increase suddenly at ~10 GPa. Previous Raman measurement reported that the highest OH stretching frequencies also increase steeply above 6 GPa. Therefore, there is a possibility that this elastic anomaly can be observed experimentally at about 6 GPa.

Kataoka R.,Tokyo Institute of Technology | Kataoka R.,Japan National Institute of Information and Communications Technology
Space Weather | Year: 2013

To calculate the probability of extreme magnetic storms in the solar cycle 24, cumulative distribution functions are investigated using an 89 year list of magnetic storms recorded at Kakioka Magnetic Observatory. It is found that the probability of occurrence of extreme magnetic storms can be modeled as a function of maximum sunspot number of a solar cycle, and the probability of another Carrington storm occurring within the next decade is estimated to be 4-6%. Key Points Probability of extreme magnetic storms in the solar cycle 24 is estimatedCumulative distribution functions of 89 year list of magnetic storms are usedProbability of another Carrington storm in the decade is estimated to be 4-6%. ©2013. American Geophysical Union. All Rights Reserved.

The fireproofing of buildings is a critical issue for the field of disaster prevention planning. In Tokyo Metropolitan Area, the amelioration of fireproofing is of particular concern, since the risk of widespread fires pursuant to a devastating earthquake is extremely high. In this study, we construct a stochastic model in order to describe the conversion process of existing structures. Using this model, we attempt to trace out a timed series of changes to structures in a given urban area and in doing so hypothetically eliminate the most hazardous areas from a disaster prevention viewpoint. In the district under consideration, we simulate time-series changes in structure by way of a rigorous application of extant urban planning and building codes. We then assess the piecemeal efficiency of such regulations and their overall effectiveness in ameliorating fire risk in potentially hazardous zones. © 2013 © 2013 Taylor & Francis.

Cui Y.,Tokyo Institute of Technology | Nakashima M.,Kyoto University
Earthquake Engineering and Structural Dynamics | Year: 2011

A series of shallowly embedded steel column bases consisting of an exposed column base and a floor slab is tested under horizontal cyclic loading to very large deformation. The effects of floor slabs on strength and ductility are examined using concrete and Steel fiber-reinforced cementitous composites (SFRCC) for the floor slab. The elastic stiffness, maximum strength, and dissipated energy of the column bases when they include SFRCC increase by 40, 70, and 70% over those of corresponding column bases with concrete floor slab. Better bonding behavior is notable for SFRCC, and the maximum strength and dissipated energy further increase by 15-30% and 70-90%, respectively, owing to the careful arrangement of reinforcing bars. Numerical models are developed to enhance the understanding the behavior of shallowly embedded column bases. Procedures for estimating the elastic stiffness and maximum strength of shallowly embedded column bases with conventional concrete are calibrated for their applicability to those with SFRCC slab. © 2011 John Wiley & Sons, Ltd.

Kawakami A.,Tokyo Institute of Technology
Development Growth and Differentiation | Year: 2010

During evolution from single-cell to multi-cellular organisms, organisms developed the needed machinery by which a vast number of functionally different types of cells could be unified into an individual. To attain this goal, organisms evolved the developmental strategies that produced different cell types and unified them into complex body architecture. However, a more intriguing feature of multi-cellular organisms is that they can maintain their bodies throughout long life. For tissue maintenance, stem and/or progenitor cells in many tissues and organs are thought to play an important role; however, we know little about their control and the process of tissue reconstitution. As cells are fragile, all animals have the ability, more or less, to replace damaged or dead cells; however, there are large variations in such abilities, depending on the type of organs and the species. Though vertebrates cannot reconstitute their bodies from a small piece as do planarians, some lower vertebrates, unlike mammals, have the ability to regenerate body appendages and many internal organs. If we unveil the nature of stem cells in striking examples of such regeneration, this information can be applied to mammals and greatly benefit us. The focus in the present review is on the recent advances in our knowledge about the regeneration mechanism in fish, including the stem cells that are involved. © 2009 Japanese Society of Developmental Biologists.

Noda N.N.,Hokkaido University | Ohsumi Y.,Tokyo Institute of Technology | Inagaki F.,Hokkaido University
FEBS Letters | Year: 2010

Autophagy is a bulk degradation system conserved among most eukaryotes. Recently, autophagy has been shown to mediate selective degradation of various targets such as aggregated proteins and damaged or superfluous organelles. Structural studies have uncovered the conserved specific interactions between autophagic receptors and Atg8-family proteins through WXXL-like sequences, which we term the Atg8-family interacting motif (AIM). AIM functions in various autophagic receptors such as Atg19 in the cytoplasm-to-vacuole targeting pathway, p62 and neighbor of BRCA1 gene 1 (NBR1) in autophagic degradation of protein aggregates, and Atg32 and Nix in mitophagy, and may link the target-receptor complex to autophagic membranes and/or their forming machineries. © 2010 Federation of European Biochemical Societies.

Nishida Y.,Tokyo Institute of Technology
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2016

The Kondo effect in condensed-matter systems manifests itself most sharply in their transport measurements. Here we propose an analogous transport signature of the orbital Kondo effect realized with ultracold atoms. Our system consists of imbalanced Fermi seas of two components of fermions and an impurity atom of different species which is confined by an isotropic potential. We first apply a π/2 pulse to transform two components of fermions into two superposition states. Their interactions with the impurity atom then cause a "transport" of fermions from majority to minority superposition states, whose numbers can be measured after applying another 3π/2 pulse. In particular, when the interaction of one component of fermions with the impurity atom is tuned close to a confinement-induced p-wave or higher partial-wave resonance, the resulting conductance is shown to exhibit the Kondo signature, i.e., universal logarithmic growth by lowering the temperature. The proposed transport measurement will thus provide a clear evidence of the orbital Kondo effect accessible in ultracold atom experiments and pave the way for developing new insights into Kondo physics. © 2016 American Physical Society.

Yoshino T.,Okayama University | Noritake F.,Tokyo Institute of Technology
Earth and Planetary Science Letters | Year: 2011

The origin of high electrical conductive anomalies in the lower crust is a long-standing and controversial problem. Although it has been proposed that saturated saline water or partial melt increases electrical conductivity, graphite film has also been recognized as a potential cause of high conductivity since the discovery of fine graphite films on the grain boundaries of high-grade metamorphic rocks. To investigate the stability of graphite film on grain boundary of silicate minerals under lower crustal conditions, electrical conductivity of graphite film on synthetic grain boundaries of quartz bicrystals was measured by means of impedance spectroscopy at 1. GPa and up to 1200. K in a multianvil apparatus. At first heating, the electrical conductivity of the thin graphite film with thickness less than 100. nm was initially very high but decreased with time during annealing. Under high temperature conditions (> 1000. K), the conductivity of a thin carbon film rapidly decreases and approaches the quartz conductivity. This indicates that graphite film on a grain boundary between two quartz crystals is not stable at high temperatures. Optical microscopic observation of the run products suggested a disconnected feature of graphite on a quartz grain boundary. Disconnection of graphite film can be caused by higher interfacial energy between graphite and silicate minerals than that of the grain boundary energy. Therefore, a thin graphite film is not a likely candidate to account for high conductivity anomalies in the middle and lower continental crust. © 2011 Elsevier B.V.

Maeda K.,Tokyo Institute of Technology | Maeda K.,Japan Science and Technology Agency
ACS Applied Materials and Interfaces | Year: 2014

Rhodium-doped barium titanate (BaTiO3:Rh) powder was prepared by the polymerized complex (PC) method, and the photocatalytic activity for H 2 evolution from water was examined. BaTiO3 is a wide-gap n-type semiconductor having a band gap of 3.0 eV. Doping Rh species into the lattice of BaTiO3 resulted in the formation of new absorption bands in visible light region. Upon visible light (λ > 420 nm), BaTiO 3:Rh modified with nanoparticulate Pt as a water reduction promoter was capable of producing H2 from water containing an electron donor such as methanol and iodide. The best material prepared by the PC method exhibited higher activity than that made by a conventional solid-state reaction method. Visible-light-driven Z-scheme water splitting was also accomplished using Pt/BaTiO3:Rh as a building block for H2 evolution in combination with PtOx-loaded WO3 as an O2 evolution photocatalyst in the presence of an IO3 -/I - shuttle redox mediator. Photoelectrochemical analysis indicated that a porous BaTiO3:Rh electrode exhibited cathodic photoresponse due to water reduction in a neutral aqueous Na2SO4 solution upon visible light. © 2014 American Chemical Society.

Kimura T.,Keio University | Kimura T.,Tokyo Institute of Technology
Journal of High Energy Physics | Year: 2016

We study two-dimensional (Formula presented.) gauge theory and its dualized system in terms of complex (linear) superfields and their alternatives. Although this technique itself is not new, we can obtain a new model, the so-called “semi-doubled” GLSM. Similar to doubled sigma model, this involves both the original and dual degrees of freedom simultaneously, whilst the latter only contribute to the system via topological interactions. Applying this to the (Formula presented.) GLSM for H-monopoles, i.e., smeared NS5-branes, we obtain its T-dualized systems in quite an easy way. As a bonus, we also obtain the semi-doubled GLSM for an exotic 52 3-brane whose background is locally nongeometric. In the low energy limit, we construct the semi-doubled NLSM which also generates the conventional string world-sheet sigma models. In the case of the NLSM for 52 3-brane, however, we find that the Dirac monopole equation does not make sense any more because the physical information is absorbed into the divergent part via the smearing procedure. This is nothing but the signal which indicates that the nongeometric feature emerges in the considering model. © 2016, The Author(s).

Akiyama M.,Waseda University | Frangopol D.M.,Lehigh University | Matsuzaki H.,Tokyo Institute of Technology
Earthquake Engineering and Structural Dynamics | Year: 2011

Over the last two decades, the probabilistic assessment of reinforced concrete (RC) structures under seismic hazard has been developed rapidly. However, little attention has been devoted to the assessment of the seismic reliability of corroded structures. For the life-cycle assessment of RC structures in a marine environment and earthquake-prone regions, the effect of corrosion due to airborne chlorides on the seismic capacity needs to be taken into consideration. Also, the effect of the type of corrosive environment on the seismic capacity of RC structures has to be quantified. In this paper, the evaluation of the displacement ductility capacity based on the buckling model of longitudinal rebars in corroded RC bridge piers is established, and a novel computational procedure to integrate the probabilistic hazard associated with airborne chlorides into life-cycle seismic reliability assessment of these piers is proposed. The seismic demand depends on the results of seismic hazard assessment, whereas the deterioration of seismic capacity depends on the hazard associated with airborne chlorides. In an illustrative example, an RC bridge pier was modeled as single degree of freedom (SDOF). The longitudinal rebars buckling of this pier was considered as the sole limit state when estimating its failure probability. The findings show that the life-cycle reliability of RC bridge piers depends on both the seismic and airborne chloride hazards, and that the cumulative-time failure probabilities of RC bridge piers located in seismic zones can be dramatically affected by the effect of airborne chlorides. © 2011 John Wiley & Sons, Ltd.

Yoshizawa M.,Tokyo Institute of Technology | Klosterman J.K.,Bowling Green State University
Chemical Society Reviews | Year: 2014

Anthracene, with its molecular panel-like shape and robust photophysical behaviour, is a versatile building block that is widely used to construct attractive and functional molecules and molecular assemblies through covalent and non-covalent linkages. The intrinsic photophysical, photochemical and chemical properties of the embedded anthracenes often interact to engender desirable chemical behaviours and properties in multi-anthracene assemblies. This review article focuses on molecular architectures with linear, cyclic, cage, and capsule shapes, each containing three or more anthracene subunits. © The Royal Society of Chemistry.

Mamiya J.-I.,Tokyo Institute of Technology
Polymer Journal | Year: 2013

An actuator is an energy transducer that can convert input energies into work. Cross-linked liquid-crystalline polymers show photoinduced deformation with changes in the molecular shape and alignment of the polymers. Polymer materials can transduce converted light energy into mechanical stress by the macroscopic deformation of the polymers (photomechanical effect). The effect of the molecular structures of the photochromic liquid-crystalline polymers on the photoinduced deformation is studied. The mechanism of the photoinduced deformation of the polymers is investigated. Three-dimensional movements of the liquid-crystalline polymers are achieved by laminating the polymers into a flexible polymer sheet. In this review, the design of the polymer materials with a photochromic moiety and an evaluation of their photomechanical effects are described. The photomodulation of the alignment of liquid-crystalline polymers and their applications for light-driven polymer actuators are summarized. © 2013 The Society of Polymer Science, Japan (SPSJ) All rights reserved.

Sakuma H.,Tokyo Institute of Technology
Journal of Geophysical Research: Solid Earth | Year: 2013

The frictional strength of faults is a critical factor that contributes to continuous fault slip and earthquake occurrence. Frictional strength can be reduced by the presence of sheet-structured clay minerals. In this study, two important factors influencing the frictional coefficient of minerals were quantitatively analyzed by a newly developed computational method based on a combination of first-principles study and thermodynamics. One factor that helps reduce the frictional coefficient is the low adhesion energy between the layers under dry conditions. Potassium ions on mica surfaces are easily exchanged with sodium ions when brought into contact with highly concentrated sodium-halide solutions. We found that the surface ion exchange with sodium ions reduces the adhesion energy, indicating that the frictional coefficient can be reduced under dry conditions. Another factor is the lubrication caused by adsorbed water films on mineral surfaces under wet conditions. Potassium and sodium ions on mica surfaces have a strong affinity for water molecules. In order to remove the adsorbed water molecules confined between mica surfaces, a differential compressive stress of the order of tens of gigapascals was necessary at room temperature. These water molecules inhibit direct contact between mineral surfaces and reduce the frictional coefficient. Our results imply that the frictional coefficient can be modified through contact with fluids depending on their salt composition. The low adhesion energy between fault-forming minerals and the presence of an adsorbed water film is a possible reason for the low frictional coefficient observed at continuous fault slip zones. © 2013. American Geophysical Union. All Rights Reserved.

Miyaji A.,Tokyo Institute of Technology
Methods in Enzymology | Year: 2011

Particulate methane monooxygenase (pMMO) catalyzes methane hydroxylation to methanol at ambient temperature and pressure. pMMO from Methylosinus trichosporium OB3b is one of the two pMMOs for which the protein structure was determined by X-ray crystallography. Because purified pMMO is inherently instable in vitro, it is difficult to use for time-consuming analysis. Therefore, investigations using crude enzyme preparations of pMMO are useful in some cases. In this chapter, methods for preparing pMMO from M. trichosporium OB3b to varying degrees of purity, including bacterial cells expressing pMMO, membrane fractions containing pMMO, and highly purified pMMO, are described. © 2011 Elsevier Inc.

Hirose K.,Tokyo Institute of Technology
Journal of the Physical Society of Japan | Year: 2013

With recent developments in x-ray diffraction (XRD) measurements at synchrotron radiation facilities, we can examine stable crystal structure and phase transition in-situ at high-pressure and -temperature (P-T) conditions corresponding to the deep Earth. MgSiO3 perovskite is a principal mineral in most parts of the lower mantle, but its stability and possible phase transition in the lowermost mantle have long been unclear. Recent synchrotron XRD experiments at SPring-8 revealed the phase transition from perovskite to post-perovskite above 120 GPa and 2400 K, the conditions at a depth of 2600-km, a few hundred kilometers above the bottom of the mantle. It is now widely accepted that post-perovskite is a primary mineral in the D″ layer. The layered crystal structure of post-perovskite causes unique physical properties such as enhanced electrical and thermal conductivity. More recent progress of synchrotron XRD measurements at ultrahigh P-T conditions is also briefly reviewed. Copyright © 2013 The Physical Society of Japan.

Masuda S.,Tokyo Institute of Technology | Masuda S.,Japan Science and Technology Agency
Plant and Cell Physiology | Year: 2013

BLUF (sensor of blue light using FAD) domain-containing proteins are one of three types of flavin-binding, blue-light-sensing proteins found in many bacteria and some algae. The other types of blue-light-sensing proteins are the cryptochromes and the light, oxygen, voltage (LOV) domain-containing proteins. BLUF proteins control a wide variety of light-dependent physiological activities including photosystem synthesis, biofilm formation and the photoavoidance response. The BLUF domain photochemical reaction is unique in that only small chromophore structural changes are involved in the light activation process, because the rigid flavin moiety is involved, rather than an isomerizable chromophore (e.g. phytochromobilin in phytochromes and retinal in rhodopsins). Recent spectroscopic, biochemical and structural studies have begun to elucidate how BLUF domains transmit the light-induced signal and identify related, subsequent changes in the domain structures. Herein, I review progress made to date concerning the physiological functions and the phototransduction mechanism of BLUF proteins. © 2012 The Author 2012. Published by Oxford University Press on behalf of Japanese Society of Plant Physiologists. All rights reserved.

Liu H.-C.,Tokyo Institute of Technology | Liu L.,Tongji University | Liu N.,Chongqing Jiaotong University
Expert Systems with Applications | Year: 2013

Failure mode and effects analysis (FMEA) is a risk assessment tool that mitigates potential failures in systems, processes, designs or services and has been used in a wide range of industries. The conventional risk priority number (RPN) method has been criticized to have many deficiencies and various risk priority models have been proposed in the literature to enhance the performance of FMEA. However, there has been no literature review on this topic. In this study, we reviewed 75 FMEA papers published between 1992 and 2012 in the international journals and categorized them according to the approaches used to overcome the limitations of the conventional RPN method. The intention of this review is to address the following three questions: (i) Which shortcomings attract the most attention? (ii) Which approaches are the most popular? (iii) Is there any inadequacy of the approaches? The answers to these questions will give an indication of current trends in research and the best direction for future research in order to further address the known deficiencies associated with the traditional FMEA. © 2012 Elsevier Ltd. All rights reserved.

Maeda K.,Tokyo Institute of Technology | Maeda K.,Japan Science and Technology Agency
Physical Chemistry Chemical Physics | Year: 2013

Water splitting to form H2 and O2 using semiconductor photocatalysts under sunlight is a possible means of clean energy production from renewable resources. (Oxy)nitrides are regarded as suitable candidates for the application, because of their suitable band edge positions, small band gaps (<3 eV), and stability under irradiation. Since early reports published in 2002 by Domen et al., it has been demonstrated that several (oxy)nitrides are active photocatalysts capable of reducing and oxidizing water in the presence of suitable electron donors and acceptors, respectively, under visible light (λ > 400 nm). Some have achieved direct water splitting into H 2 and O2 with good reproducibility. (Oxy)nitrides are also attractive as water-splitting photoelectrodes, and highly efficient photoelectrochemical water splitting has been accomplished using tantalum-based (oxy)nitrides under visible light with good stability. However, there still remain a lot of challenges that have to be addressed in this research field. This perspective highlights recent progress in the development of (oxy)nitride materials for application in photocatalytic and photoelectrochemical water splitting made by the author and his colleagues, especially in the last 5 years. © 2013 the Owner Societies.

Hosono H.,Tokyo Institute of Technology
Japanese Journal of Applied Physics | Year: 2013

Ceramics, one of the earliest materials used by humans, have been used since the Stone Age and are also one of the core materials supporting modern society. In this article, I will review the features of transparent oxides, the main components of ceramics, and the progress of research on their electro-active functionalities from the viewpoint of material design. Specifically, the emergence of the functionality of the cement component 12CaO 7Al2O3, the application of transparent oxide semiconductors to thin-film transistors for flat panel displays, and the design of wide-gap ptype semiconductors are introduced along with the progress in their research. In addition, oxide semiconductors are comprehensively discussed on the basis of the band lineup. © 2013 The Japan Society of Applied Physics.

Michinobu T.,Tokyo Institute of Technology
Yuki Gosei Kagaku Kyokaishi/Journal of Synthetic Organic Chemistry | Year: 2013

The rapid growth of the click chemistry concept produced a wide variety of functional polymers. In this research field, polymeric ion sensors, which can recognize specific metal cations or anions, have mainly been synthesized by the Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC). However, due to several disadvantages suggested for the CuAAC, the development of new types of click chemistry reactions has recently started. Among them, it was found that the high-yielding addition reactions between electron-rich alkynes and cyano-based acceptors offer promising application possibilities as polymeric chemosensors. The donor-acceptor type products feature intense charge-transfer bands in the visible region. The recognition of some specific metal cations or anions resulted in well-defined visible colorimetric changes in the optical spectra.

Yamamoto T.,Tokyo Institute of Technology
Polymer Journal | Year: 2013

In comparison with their linear counterparts, cyclic polymers exhibit distinctive properties due to their topology. The synthesis of cyclic polymers and the functionalities arising from their unique shapes, namely topology effects, are reviewed. The electrostatic self-assembly and covalent fixation (ESA-CF) process was used in conjunction with click chemistry and with olefin metathesis to construct selectively a variety of unprecedented polymer architectures, such as manacle-shaped and tandem multicycles, as well as doubly fused tricyclic and triply fused tetracyclic topologies. Moreover, the self-assembly of a cyclic amphiphilic block copolymer, which was prepared by intramolecular metathesis, produced micelles that exhibited an increase in thermal stability of approximately 50 °C compared with the micelles formed from the linear prepolymer. Single-molecule spectroscopic studies also revealed different diffusion modes for cyclic and linear polymers. © 2013 The Society of Polymer Science, Japan (SPSJ) All rights reserved.

Nasu J.,Tokyo Institute of Technology | Udagawa M.,University of Tokyo | Motome Y.,University of Tokyo
Physical Review Letters | Year: 2014

The quantum spin liquid is an exotic quantum state of matter in magnets. This state is a spin analog of liquid helium that does not solidify down to the lowest temperature due to strong quantum fluctuations. In conventional fluids, the liquid and gas possess the same symmetry and adiabatically connect to each other by bypassing the critical end point. We find that the situation is qualitatively different in quantum spin liquids realized in a three-dimensional Kitaev model; both gapless and gapped quantum spin liquid phases at low temperatures are always distinguished from the high-temperature paramagnet (spin gas) by a phase transition. The results challenge the common belief that the absence of thermodynamic singularity down to the lowest temperature is a symptom of a quantum spin liquid. © 2014 American Physical Society.

Hoshina T.,Tokyo Institute of Technology
Nippon Seramikkusu Kyokai Gakujutsu Ronbunshi/Journal of the Ceramic Society of Japan | Year: 2013

The size effect of ferroelectric materials is one of the most important issues to develop next-generation dielectric devices. In this paper, we reviewed our studies on the size effects of barium titante (BaTiO3) fine particles and ceramics. In the size effect of BaTiO3 fine particles, the maximum of dielectric permittivity was observed at a particle size of around 140 nm, and was explained by the composite structure model including a gradient lattice strain layer (GLSL) having a very high permittivity. In contrast, the grain size effect of BaTiO3 ceramics, where the permittivity showed a maximum at a grain size of about 1.1 μm, was interpreted as the superposition effect of domain-wall contributions and grain boundary effect. © 2013 The Ceramic Society of Japan. All rights reserved.

Nakatogawa H.,Tokyo Institute of Technology
Essays in Biochemistry | Year: 2013

In autophagy, the autophagosome, a transient organelle specialized for the sequestration and lysosomal or vacuolar transport of cellular constituents, is formed via unique membrane dynamics. This process requires concerted actions of a distinctive set of proteins named Atg (autophagy-related). Atg proteins include two ubiquitin- like proteins, Atg12 and Atg8 [LC3 (light-chain 3) and GABARAP (ã-aminobutyric acid receptor-associated protein) in mammals]. Sequential reactions by the E1 enzyme Atg7 and the E2 enzyme Atg10 conjugate Atg12 to the lysine residue in Atg5, and the resulting Atg12-Atg5 conjugate forms a complex with Atg16. On the other hand, Atg8 is first processed at the C-terminus by Atg4, which is related to ubiquitin-processing/deconjugating enzymes. Atg8 is then activated by Atg7 (shared with Atg12) and, via the E2 enzyme Atg3, finally conjugated to the amino group of the lipid PE (phosphatidylethanolamine). The Atg12-Atg5-Atg16 complex acts as an E3 enzyme for the conjugation reaction of Atg8; it enhances the E2 activity of Atg3 and specifies the site of Atg8-PE production to be autophagy-related membranes. Atg8-PE is suggested to be involved in autophagosome formation at multiple steps, including membrane expansion and closure. Moreover, Atg4 cleaves Atg8-PE to liberate Atg8 from membranes for reuse, and this reaction can also regulate autophagosome formation. Thus these two ubiquitin-like systems are intimately involved in driving the biogenesis of the autophagosomal membrane. © 2013 Biochemical Society.

Takezoe H.,Tokyo Institute of Technology | Gorecka E.,University of Warsaw | Cepic M.,Jozef Stefan Institute | Cepic M.,University of Ljubljana
Reviews of Modern Physics | Year: 2010

This paper reviews nearly 20 years of research related to antiferroelectric liquid crystals and gives a short overview of possible applications. "Antiferroelectric liquid crystals" is the common name for smectic liquid crystals formed of chiral elongated molecules that exhibit a number of smectic (Sm) tilted structures with variation of the strong-tilt azimuthal direction from layer to layer (i.e., nonsynclinic structures). The phases have varying crystallographic unit periodicity from a few (Sm Cα*), four (Sm C FI2 *), three (Sm C FI1 *), and two (Sm CA*) smectic layers and all of the phases possess liquidlike order inside the layer. The review describes the discovery of these phases and various methods used for their identification and to determine their structures and their properties. A theoretical description of these systems is also given; one of the models-the discrete phenomenological model-of antiferroelectric liquid crystals is discussed in detail as this model allows for an explanation of phase structures and observed phase sequences under changes of temperature or external fields that is most consistent with experimental results. © 2010 The American Physical Society.

Terasaki N.,Tokyo Institute of Technology
PloS one | Year: 2013

The Long interspersed element 1 (LINE1 or L1) retrotransposon constitutes 17% of the human genome. There are currently 80-100 human L1 elements that are thought to be active in any diploid human genome. These elements can mobilize into new locations of the genome, resulting in changes in genomic information. Active L1s are thus considered to be a type of endogenous mutagen, and L1 insertions can cause disease. Certain stresses, such as gamma radiation, oxidative stress, and treatment with some agents, can induce transcription and/or mobilization of retrotransposons. In this study, we used a reporter gene assay in HepG2 cells to screen compounds for the potential to enhance the transcription of human L1. We assessed 95 compounds including genotoxic agents, substances that induce cellular stress, and commercially available drugs. Treatment with 15 compounds increased the L1 promoter activity by >1.5-fold (p<0.05) after 6 or 24 hours of treatment. In particular, genotoxic agents (benzo[a]pyrene, camptothecin, cytochalasin D, merbarone, and vinblastine), PPARα agonists (bezafibrate and fenofibrate), and non-steroidal anti-inflammatory drugs (diflunisal, flufenamic acid, salicylamide, and sulindac) induced L1 promoter activity. To examine their effects on L1 retrotransposition, we developed a high-throughput real-time retrotransposition assay using a novel secreted Gaussia luciferase reporter cassette. Three compounds (etomoxir, WY-14643, and salicylamide) produced a significant enhancement in L1 retrotransposition. This is the first study to report the effects of a wide variety of compounds on L1 transcription and retrotransposition. These results suggest that certain chemical- and drug-induced stresses might have the potential to cause genomic mutations by inducing L1 mobilization. Thus, the risk of induced L1 transcription and retrotransposition should be considered during drug safety evaluation and environmental risk assessments of chemicals.

Miyazaki R.,Tokyo Institute of Technology
Journal of the Physical Society of Japan | Year: 2013

We conjecture the existence of a relationship between frustration and the transition point at zero temperature of Ising spin glasses. The relation reveals that, in several Ising spin glass models, the concentration of ferromagnetic bonds is close to the critical concentration at zero temperature when the output of a function about frustration is equal to unity. The function is the derivative of the average number of frustrated plaquettes with respect to the average number of antiferromagnetic bonds. This relation is conjectured in Ising spin glasses with binary couplings on two-dimensional lattices, hierarchical lattices, and three-body Ising spin glasses with binary couplings on two-dimensional lattices. In addition, the same argument in the Sherrington-Kirkpatrick model yields a point that is identical to the replicasymmetric solution of the transition point at zero temperature.

Mori T.,Tokyo Institute of Technology
Journal of the Physical Society of Japan | Year: 2013

Zero-gap states in organic conductors are investigated from the viewpoint of network of the transfer integrals. The method for characterizing topological insulators is applied to organic conductors, from which we can predict the existence of a band contact point by examining the parity of the non-diagonal element of Hamiltonian at the timereversal invariant momenta (TRIM). β''-(BEDT-TTF)3(ClO4)2 [BEDT-TTF. bis(ethylenedithio)tetrathiafulvalene] is a prototypical example to demonstrate the influence of non-stripe charge order, where the energy level of the molecule on an inversion center deepens owing to the charge order, and the remaining molecules construct a distorted honeycomb lattice similar to graphene, leading to a Dirac point. The same mechanism applies to the appearance of the Dirac point in α-(BEDT-TTF)2I3. © 2013 The Physical Society of Japan.

Terashima Y.,Tokyo Institute of Technology | Yamazaki M.,Princeton University
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2013

We provide quantitative evidence for our previous conjecture which states an equivalence of the partition function of a 3d N=2 gauge theory on a duality wall and that of the SL(2,R) Chern-Simons theory on a mapping torus, for a class of examples associated with once-punctured torus. In particular, we demonstrate that a limit of the 3d N=2 partition function reproduces the hyperbolic volume and the Chern-Simons invariant of the mapping torus. This is shown by analyzing the classical limit of the trace of an element of the mapping class group in the Hilbert space of the quantum Teichmüller theory. We also show that the subleading correction to the partition function reproduces the Reidemeister torsion. © 2013 American Physical Society.

Hyodo T.,Tokyo Institute of Technology
Physical Review Letters | Year: 2013

We study the structure of two-body s-wave bound states as well as resonances in the threshold energy region. We focus on the single-channel scattering where the scattering length and the effective range are given by real numbers. It is shown that, in the energy region where the effective range expansion is valid, the properties of resonances are constrained only by the position of the pole. We find that the compositeness defined through the analytic continuation of the field renormalization constant is purely imaginary and normalized for resonances. We discuss the interpretation of this quantity by examining the structure of the hadron resonance Λc(2595) in the πΣc scattering. We show that the Λ c(2595) resonance requires an unnaturally large effective range and hence it is not likely a πΣc molecule. © 2013 American Physical Society.

Nishida Y.,Tokyo Institute of Technology
Physical Review Letters | Year: 2013

We propose a simple but novel scheme to realize the Kondo effect with ultracold atoms. Our system consists of a Fermi sea of spinless fermions interacting with an impurity atom of different species which is confined by an isotropic potential. The interspecies attraction can be tuned with an s-wave Feshbach resonance so that the impurity atom and a spinless fermion form a bound dimer that occupies a threefold-degenerate p orbital of the confinement potential. Many-body scatterings of this dimer and surrounding spinless fermions occur with exchanging their angular momenta and thus exhibit the SU(3) orbital Kondo effect. The associated Kondo temperature has a universal leading exponent given by TK exp ¡[-π/(3apkF3)] that depends only on an effective p-wave scattering volume ap and a Fermi wave vector kF. We also elucidate a Kondo singlet formation at zero temperature and an anisotropic interdimer interaction mediated by surrounding spinless fermions. The Kondo effect thus realized in ultracold atom experiments may be observed as an increasing atom loss by lowering the temperature or with radio-frequency spectroscopy. Our scheme and its extension to a dense Kondo lattice will be useful to develop new insights into yet unresolved aspects of Kondo physics. © 2013 American Physical Society.

Kobayashi T.,Rikkyo University | Tanahashi N.,University of Tokyo | Yamaguchi M.,Tokyo Institute of Technology
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2013

We propose a multifield extension of (generalized) G inflation, based on covariant multi-Galileons and their generalization preserving second-order field equations. We compute the quadratic action for cosmological perturbations. By comparing the formulas for cosmological perturbations, it is highlighted that multifield Dirac-Born-Infield Galileon inflation is not included in the multifield version of generalized G inflation. Our result indicates that the generalized covariant multi-Galileon theory is not the most general multi-scalar-tensor theory with second-order field equations. © 2013 American Physical Society.

Gruneis A.,University of Vienna | Kresse G.,University of Vienna | Hinuma Y.,Kyoto University | Oba F.,Kyoto University | Oba F.,Tokyo Institute of Technology
Physical Review Letters | Year: 2014

The ionization potential is a fundamental key quantity with great relevance to diverse material properties. We find that state of the art methods based on density functional theory and simple diagrammatic approaches as commonly taken in the GW approximation predict the ionization potentials of semiconductors and insulators unsatisfactorily. Good agreement between theory and experiment is obtained only when diagrams resulting from the antisymmetry of the many-electron wave function are taken into account via vertex corrections in the self-energy. The present approach describes both localized and delocalized states accurately, making it ideally suited for a wide class of materials and processes. © 2014 American Physical Society.

Onaka S.,Tokyo Institute of Technology
Philosophical Magazine Letters | Year: 2010

The Hencky strain is an appropriate measure for large deformation where principal directions of strains rotate. In this study, the equivalent strain in large simple shear deformation is re-examined using the Hencky strain. When the amount of simple shear is γ, the equivalent strain of the Hencky strain becomes a logarithmic function of γ, which is the same as the result given by Eichinger [Festigkeitstheoretische untersuchungen, in Handbuch der Werkstoffprüfung, E. Siebel, ed., 2nd ed., Springer, Berlin, 1955, p.715]. © 2010 Taylor & Francis.

Shibayama S.,Tokyo Institute of Technology
Soils and Foundations | Year: 2010

The paper describes observed behaviour of a model tunnel embedded in dry sand subjected to cyclic ground shear deformation in a centrifuge, as well as the behaviour of the model ground during shear deformation. Detailed data on earth pressures acting on the tunnel lining and the sectional forces of the lining are presented during ground shear deformation. The data suggest that the earth pressure at tunnel crown before ground shear deformation is smaller than the full overburden pressure probably due to the formation of arch action and the arch action may deteriorate with the cyclic ground shear deformation, resulting in an increase in the earth pressure at crown and changing the distribution of the sectional forces, which are largely influenced by conditions between tunnel lining and invert.

Nagata Y.,Tokyo Institute of Technology | Soler D.,Polytechnic University of Valencia
Expert Systems with Applications | Year: 2012

The asymmetric traveling salesman problem (ATSP) is one of the most important combinatorial optimization problems. It allows us to solve, either directly or through a transformation, many real-world problems. We present in this paper a new competitive genetic algorithm to solve this problem. This algorithm has been checked on a set of 153 benchmark instances with known optimal solution and it outperforms the results obtained with previous ATSP heuristic methods. © 2012 Elsevier Ltd. All rights reserved.

Kimura T.,Tokyo Institute of Technology | Sasaki S.,Kitasato University | Yata M.,High Energy Accelerator Research Organization
Journal of High Energy Physics | Year: 2014

We construct world-volume effective actions of exotic 52 2-branes in type IIA and IIB string theories. The effective actions are given in fully space-time covariant forms with two Killing vectors associated with background isometries. The effective theories are governed by the six-dimensional N = (2, 0) tensor multiplet and N = (1, 1) vector multiplet, respectively. Performing the S-duality transformation to the 52 2-brane effective action in type IIB string theory, we also work out the world-volume action of the 52 3-brane. We discuss some additional issues relevant to the exotic five-branes in type I and heterotic string theories. © The Authors.

Takahashi K.,Tokyo Institute of Technology
Journal of Physics A: Mathematical and Theoretical | Year: 2013

We study the assisted adiabatic passage, and equivalently the transitionless quantum driving, as a quantum brachistochrone trajectory. The optimal Hamiltonian for given constraints is constructed from the quantum brachistochrone equation. We discuss how the adiabatic passage is realized as the solution of the equation. The formulation of the quantum brachistochrone is based on the principle of least action. We utilize it to discuss the stability of the adiabatic passage. © 2013 IOP Publishing Ltd.

Sakata A.,Tokyo Institute of Technology
Journal of Physics A: Mathematical and Theoretical | Year: 2013

Asynchronous dynamics given by the master equation in the Sherrington-Kirkpatrick (SK) spin-glass model is studied based on dynamical replica theory (DRT) with an extension to take into account the autocorrelation function. The dynamical behaviour of the system is approximately described by dynamical equations of the macroscopic quantities: magnetization, energy contributed by randomness and the autocorrelation function. The dynamical equations under the replica symmetry assumption are derived by introducing the subshell equipartitioning assumption and exploiting the replica method. The obtained dynamical equations are compared with Monte Carlo simulations, and it is demonstrated that the proposed formula describes well the time evolution of the autocorrelation function in some parameter regions. The study offers a reasonable description of the autocorrelation function in the SK spin-glass system. © 2013 IOP Publishing Ltd.

Kurokawa H.,Nagoya University | Nakamoto T.,Tokyo Institute of Technology
Astrophysical Journal | Year: 2014

During their evolution, short-period exoplanets may lose envelope mass through atmospheric escape owing to intense X-ray and extreme ultraviolet (XUV) radiation from their host stars. Roche-lobe overflow induced by orbital evolution or intense atmospheric escape can also contribute to mass loss. To study the effects of mass loss on inner planet populations, we calculate the evolution of hot Jupiters considering mass loss of their envelopes and thermal contraction. Mass loss is assumed to occur through XUV-driven atmospheric escape and the following Roche-lobe overflow. The runaway effect of mass loss results in a dichotomy of populations: hot Jupiters that retain their envelopes and super Earths whose envelopes are completely lost. Evolution primarily depends on the core masses of planets and only slightly on migration history. In hot Jupiters with small cores (≃ 10 Earth masses), runaway atmospheric escape followed by Roche-lobe overflow may create sub-Jupiter deserts, as observed in both mass and radius distributions of planetary populations. Comparing our results with formation scenarios and observed exoplanets populations, we propose that populations of closely orbiting exoplanets are formed by capturing planets at/inside the inner edges of protoplanetary disks and subsequent evaporation of sub-Jupiters. © 2014. The American Astronomical Society. All rights reserved..

Takahashi F.,Tokyo Institute of Technology | Shimizu H.,University of Tokyo
Journal of Fluid Mechanics | Year: 2012

Mechanisms of magnetic field intensification by flows of an electrically conducting fluid in a rapidly rotating spherical shell are investigated using a numerical dynamo model with an Ekman number of 10 -5. A strong dipolar solution with a magnetic energy 55 times larger than the kinetic energy of thermal convection is obtained. In a regime of small viscosity and inertia with the strong magnetic field, the convection structure consists of a few large-scale retrograde flows in the azimuthal direction and localized thin sheet-like plumes. A detailed term-by-term analysis of the magnetic field amplification processes shows that the magnetic field is amplified through stretching of magnetic lines, which occurs typically through four types of flow: the retrograde azimuthal flow near the outer boundary, the downwelling flow of the sheet plume, the prograde azimuthal flow near the rim of the tangent cylinder, and the cylindrical-radially alternating flows of the plume cluster. The current loop structure emerges as a result of stretching the magnetic lines along the magnetic field by the flow acceleration. The most remarkable effects of the generated magnetic field on the flow come from the strong azimuthal (toroidal) magnetic field. Similarities of the present model in the convection and magnetic field structures to previous studies at larger and even smaller Ekman numbers suggest universality of the dynamo mechanism in rotating spherical dynamos. © 2012 Cambridge University Press.

Tsubouchi K.,Tokyo Institute of Technology
Astrophysical Journal | Year: 2014

Hybrid simulations are performed to investigate the dynamics of both solar wind protons and interplanetary pickup ions (PUIs) around the corotating interaction region (CIR). The one-dimensional system is applied in order to focus on processes in the direction of CIR propagation. The CIR is bounded by forward and reverse shocks, which are responsible for particle acceleration. The effective acceleration of solar wind protons takes place when the reverse shock (fast wind side) favors a quasi-parallel regime. The diffusive process accounts for this acceleration, and particles can gain energy in a suprathermal range (on the order of 10 keV). In contrast, the PUI acceleration around the shock differs from the conventional model in which the motional electric field along the shock surface accelerates particles. Owing to their large gyroradius, PUIs can gyrate between the upstream and downstream, several proton inertial lengths away from the shock. This "cross-shock" gyration results in a net velocity increase in the field-aligned component, indicating that the magnetic mirror force is responsible for acceleration. The PUIs that remain in the vicinity of the shock for a long duration (tens of gyroperiods) gain much energy and are reflected back toward the upstream. These reflected energetic PUIs move back and forth along the magnetic field between a pair of CIRs that are magnetically connected. The PUIs are repeatedly accelerated in each reflection, leading to a maximum energy gain close to 100 keV. This mechanism can be evaluated in terms of "preacceleration" for the generation of anomalous cosmic rays. © 2014. The American Astronomical Society. All rights reserved.

Gridnev I.D.,Tokyo Institute of Technology | Gridnev I.D.,Tohoku University | Vorobiev A.Kh.,Moscow State University
ACS Catalysis | Year: 2012

The relative abundance of various species in the reaction pool of the Soai autoamplification reaction was estimated by large-scale density functional theory (DFT) computations involving calculations of the thermodynamic parameters in solution. Detailed conformational analysis of the macrocyclic tetrameric species formed by dimerization of the Zn-O-Zn-O square dimers and of their ZnPr 2 i adducts revealed the structural diversification of the homo- and heterochiral species. Homochiral tetramers are exclusively formed in a specific brandyglass conformation with almost orthogonal pyrimidinyl rings that is virtually unaffected by the formation of a ZnPr 2 i adduct. On the other hand, for heterochiral tetramers the stabilities of brandyglass and layer conformations are approximately equal. The three-dimensional (3D) cavity observed in the ZnPr 2 i adduct of the homochiral brandyglass tetramer forms an ideal chiral pocket for the coordination of the aldehyde followed by perfectly enantioselective alkylation yielding monomeric alcoholate of the same handedness as the tetrameric catalyst. Similar cavity in the heterochiral brandyglass tetramer is significantly less spacious. Moreover, the cavity practically disappears upon the coordination of ZnPr 2 i, hence the heterochiral tetramers are excluded from the flow of catalysis that leads to the realization of Frank's scheme for chiral amplification. © 2012 American Chemical Society.

Iwamoto M.,Tokyo Institute of Technology
Molecules | Year: 2011

Increased propene production is presently one of the most significant objectives in petroleum chemistry. Especially the one-step conversion of ethene to propene (ETP reaction, 3C 2H 4 → 2C 3H 6) is the most desired process. In our efforts, nickel ion-loaded mesoporous silica could turn a new type of ETP reaction into reality. The one-step conversion of ethene was 68% and the propene selectivity was 48% in a continuous gas-flow system at 673 K and atmospheric pressure. The reactivity of lower olefins and the dependences of the ETP reaction on the contact time and the partial pressure of ethene were consistent with a reaction mechanism involving dimerization of ethene to 1-butene, isomerization of 1-butene to 2-butene, and metathesis of 2-butene and ethene to yield propene. The reaction was then expanded to an ethanol-to-propene reaction on the same catalyst, in which two possible reaction routes are suggested to form ethene from ethanol. The catalysts were characterized mainly by EXAFS and TPR techniques. The local structures of the nickel species active for the ETP reaction were very similar to that of layered nickel silicate, while those on the inert catalysts were the same as that of NiO particles. © 2011 by The Authors.

Hongoh Y.,Tokyo Institute of Technology
Cellular and Molecular Life Sciences | Year: 2011

Termites thrive on dead plant matters with the aid of microorganisms resident in their gut. The gut microbiota comprises protists (single-celled eukaryotes), bacteria, and archaea, most of which are unique to the termite gut ecosystem. Although this symbiosis has long been intriguing researchers of both basic and applied sciences, its detailed mechanism remains unclear due to the enormous complexity and the unculturability of the microbiota. In the effort to overcome the difficulty, recent advances in omics, such as metagenomics, metatranscriptomics, and metaproteomics have gradually unveiled the black box of this symbiotic system. Genomics targeting a single species of the unculturable microbial members has also provided a great progress in the understanding of the symbiotic interrelationships among the gut microorganisms. In this review, the symbiotic system organized by wood-feeding termites and their gut microorganisms is outlined, focusing on the recent achievement in omics studies of this multilayered symbiotic system. © 2011 Springer Basel AG.

Konagai M.,Tokyo Institute of Technology
Japanese Journal of Applied Physics | Year: 2011

In this report, an overview of the recent status of photovoltaic (PV) power generation is first presented from the viewpoint of reducing CO2 emission. Next, the Japanese roadmap for the research and development (R&D) of PV power generation and the progress in the development of various solar cells are explained. In addition, the present status and future prospects of amorphous silicon (a-Si) thin-film solar cells, which are expected to enter the stage of full-scale practical application in the near future, are described. For a-Si single-junction solar cells, the conversion efficiency of their large-area modules has now reached 6-8%, and their practical application to megawatt solar systems has started. Meanwhile, the focus of R&D has been shifting to a-Si and microcrystalline silicon (μc-Si) tandem solar cells. Thus far, a-Si/μc-Si tandem solar cell modules with conversion efficiency exceeding 13% have been reported. In addition, triple-junction solar cells, whose target year for practical application is 2025 or later, are introduced, as well as innovative thin-film full-spectrum solar cells, whose target year of realization is 2050. © 2011 The Japan Society of Applied Physics.

Nakajima A.,Tokyo Institute of Technology
NPG Asia Materials | Year: 2011

Technologies related to hydrophobic coatings have been applied to various industrial items for droplet formation and removal from solid surfaces. However, for such surfaces, excellent water-shedding properties and droplet control in a desired direction are not easily attainable merely by reducing their surface energies. Success requires the design and control of a nanolevel surface structure with appropriate chemical composition. Various hydrophobic surfaces have been developed to date, and their static hydrophobicity has been investigated carefully. Moreover, studies of dynamic hydrophobicity of droplets have increased recently because of the rapid advance and availability of high-speed cameras, facilitating direct evaluation of droplet motion. This paper presents a review of recent studies investigating the design of hydrophobic surfaces for liquid droplet control, specifically focussing on recent studies of dynamic hydrophobicity. © 2011 Tokyo Institute of Technology.

Mori T.,Tokyo Institute of Technology
Chemistry Letters | Year: 2011

Electron donors and acceptors such as tetrathiafulvalene (TT7) and tetracyanoquinodimethane (TCNQ), which have been long known as components of organic metals, act as p- and n-channel organic semiconductors in organic field-effect transistors. High performance, good thin-film properties, and long-term stability have been achieved on the basis of appropriate molecular design. In addition, their charge-transfer complexes work as the active layers as well as conducting electrode materials showing low contact resistance. © 2011 The Chemical Society of Japan.

Michinobu T.,Tokyo Institute of Technology | Michinobu T.,Japan Science and Technology Agency
Chemical Society Reviews | Year: 2011

After the historical development from the insoluble polyacetylene film to soluble and processible aromatic polymers, donor-acceptor-type aromatic polymers have recently emerged as a new class of semiconducting polymers. The polymer energy levels and band gaps can be tuned by the appropriate selection of the donor and acceptor moieties, and some of these polymers showed good optoelectronic or photovoltaic performances. The conventional synthetic method for achieving donor-acceptor-type aromatic polymers is based on the metal-catalyzed polycondensation between donor-type monomers and acceptor-type co-monomers. In this tutorial review, a new methodology for introducing donor-acceptor chromophores into semiconducting polymers is described. The donor-acceptor structures are constructed in the main chains and side chains of semiconducting polymers using a polymer reaction based on high-yielding addition reactions between the electron-rich alkynes and strong acceptor molecules, such as tetracyanoethylene (TCNE) and 7,7,8,8-tetracyanoquinodimethane (TCNQ). Considering the p-type doping features of TCNE and TCNQ, the experimental procedure is the same as the conventional doping technique for semiconducting polymers. However, the resulting donor-acceptor type polymers are chemically stable due to the absence of unstable unpaired electrons (polarons). The donor-acceptor alternating polymers were achieved in one step from the precursor poly(aryleneethynylene)s and poly(arylenebutadiynylene)s. When the side chain alkynes were post-functionalized, the polymer energy levels were controlled by the species and amount of the employed acceptor molecules. These atom-economic acceptor additions satisfy most of the requirements of the "click chemistry" concept. In contrast to the conventional click chemistry reactions, the reactions between electron-rich alkynes and acceptor molecules provide a wide variety of polymers with promising optoelectronic applications. © 2011 The Royal Society of Chemistry.

Nakao H.,Tokyo Institute of Technology | Yanagita T.,Osaka Electro-Communication University | Kawamura Y.,Japan Agency for Marine - Earth Science and Technology
Physical Review X | Year: 2014

Reaction-diffusion systems can describe a wide class of rhythmic spatiotemporal patterns observed in chemical and biological systems, such as circulating pulses on a ring, oscillating spots, target waves, and rotating spirals. These rhythmic dynamics can be considered limit cycles of reaction-diffusion systems. However, the conventional phase-reduction theory, which provides a simple unified framework for analyzing synchronization properties of limit-cycle oscillators subjected to weak forcing, has mostly been restricted to low-dimensional dynamical systems. Here, we develop a phase-reduction theory for stable limit-cycle solutions of reaction-diffusion systems with infinite-dimensional state space. By generalizing the notion of isochrons to functional space, the phase-sensitivity function-a fundamental quantity for phase reduction-is derived. For illustration, several rhythmic dynamics of the FitzHugh-Nagumo model of excitable media are considered. Nontrivial phase-response properties and synchronization dynamics are revealed, reflecting their complex spatiotemporal organization. Our theory will provide a general basis for the analysis and control of spatiotemporal rhythms in various reaction-diffusion systems.

Lu L.,G5 8 | Namioka T.,G5 8 | Yoshikawa K.,Tokyo Institute of Technology
Applied Energy | Year: 2011

The conversion of municipal solid wastes (MSW) to energy for co-combustion with coal may be a viable MSW disposal solution from the view point of suppression of the environmental pollution as well as reduction of coal consumption. This paper describes the application of innovative hydrothermal technology on different kinds of MSW to produce powder-like solid products appropriate for co-combustion with coal. In this work, three kinds of surrogated MSW (Japanese MSW, Indian MSW and Chinese MSW) different in composition and characteristics were subjected to the hydrothermal treatment (HT) at 220°C and 2.4. MPa for 30. min. After the HT, the combustion behaviors of the samples were determined by investigating the sample weight loss (TG) and the rate of weight loss (DTG) through the thermogravimetric analysis (TGA). In addition, the effects of the HT on the characteristics and the combustion behaviors of the MSW were explored by comparing with three standard samples such as rice, cellulose and polypropylene (PP) both before and after the HT. The results obtained in this study can be drawn as the following: The HT is capable for converting MSW into uniform powder samples with low moisture content, regular shapes and high bulk density. During the HT, the hydrolysis reaction leads to the loss in volatile matter and the carbonization results in the gain in fixed carbon. The higher heating values of the three kinds of MSW after the HT are enhanced by 1.01-1.41 times (energy content per weight) and 6.39-9.00 times (energy content per volume). The combustion behaviors of the MSW in this study before the HT were dominated by the substance major in weight whereas for the ones after the HT, the intrinsic characteristics of the MSW can play an important role in determining the combustion behaviors. © 2011 Elsevier Ltd.

Shimojima M.,Tokyo Institute of Technology
Progress in Lipid Research | Year: 2011

Higher-plant chloroplast membranes are composed primarily of four characteristic lipids, namely monogalactosyldiacylglycerol, digalactosyldiacylglycerol, sulfoquinovosyldiacylglycerol (SQDG), and phosphatidylglycerol. Among them, SQDG is the only sulfur-containing anionic glycerolipid and is the least prevalent component of photosynthetic membrane lipids. SQDG biosynthesis is mostly mediated by UDP-sulfoquinovose synthase (SQD1) and SQDG synthase (SQD2). Recently, another essential gene for SQDG synthesis, UGP3, was identified using transcriptome coexpression analysis and reverse genetics. UGP3 is a novel plastid UDP-glucose pyrophosphorylase that supplies UDP-glucose to SQD1 in plastids. In Arabidopsis, SQDG is dispensable under normal growth conditions but important in certain environments, particularly phosphate-depleted conditions. The function of SQDG under phosphate-limited growth conditions is highly correlated with the regulation of other plant glycerolipid biosyntheses. This review summarizes recent research defining the mechanism for SQDG biosynthesis and its biological function in higher plants, particularly under phosphate-starved conditions. © 2011 Elsevier Ltd. All rights reserved.

Murakami Y.,Ehime University | Tanaka M.,Tokyo Institute of Technology
Developmental Biology | Year: 2011

The evolution and diversification of vertebrate behaviors associated with locomotion depend highly on the functional transformation of paired appendages. Although the evolution of fins into limbs has long been a focus of interest to scientists, the evolution of neural control during this transition has not received much attention. Recent studies have provided significant progress in the understanding of the genetic and developmental bases of the evolution of fin/limb motor circuitry in vertebrates. Here we compare the organization of the motor neurons in the spinal cord of various vertebrates. We also discuss recent advances in our understanding of these events and how they can provide a mechanistic explanation for the evolution of fin/limb motor circuitry in vertebrates. © 2011 Elsevier Inc.

Preobraschenski J.,Max Planck Institute for Biophysical Chemistry | Zander J.-F.,Charite - Medical University of Berlin | Suzuki T.,Waseda University | Suzuki T.,Tokyo Institute of Technology | And 2 more authors.
Neuron | Year: 2014

Vesicular glutamate transporters (VGLUTs) accumulate the neurotransmitter glutamate in synaptic vesicles. Transport depends on a V-ATPase-dependent electrochemical proton gradient (δμH+) and requires chloride ions, but how chloride acts and how ionic and charge balance is maintained during transport is controversial. Using a reconstitution approach, we used an exogenous proton pump to drive VGLUT-mediated transport either in liposomes containing purified VGLUT1 or in synaptic vesicles fused with proton-pump-containing liposomes. Our data show that chloride stimulation can be induced at both sides of the membrane. Moreover, chloride competes withglutamate at high concentrations. In addition, VGLUT1 possesses a cation binding site capable of binding H+ or K+ ions, allowing for proton antiport or K+/H+ exchange. We conclude that VGLUTs contain two anion binding sites and one cation binding site, allowing the transporter to adjust to the changing ionic conditions during vesicle filling without being dependent on other transporters or channels. © 2014 Elsevier Inc.

Kudo A.,Tokyo Institute of Technology
Cellular and Molecular Life Sciences | Year: 2011

More than 10 years have passed since the naming of periostin derived from its expression sites in the periosteum and periodontal ligament. Following this finding, we have accumulated more data on the expression patterns of periostin, and, finally, with the generation of periostin-deficient mice, have revealed functions of periostin in the regeneration of tissues in bone, tooth, heart, and skin, and its action in cancer invasion. Since periostin is a matricellular protein, the first investigation of periostin function showed its enhancement of cell migration by acting outside the cell. On the other hand, recent observations have demonstrated that periostin functions in fibrillogenesis in association with extracellular matrix molecules inside the cell. © 2011 Springer Basel AG.

Obara K.,Hokkaido University | Ohsumi Y.,Tokyo Institute of Technology
International Journal of Cell Biology | Year: 2011

Phosphorylation of phosphatidylinositol (PtdIns) by a PtdIns 3-kinase is an essential process in autophagy. Atg14, a specific subunit of one of the PtdIns 3-kinase complexes, targets the complex to the probable site of autophagosome formation, thereby, sorting the complex to function specifically in autophagy. The N-terminal half of Atg14, containing coiled-coil domains, is required to form the PtdIns 3-kinase complex and target it to the proper site. The C-terminal half of yeast Atg14 is suggested to be involved in the formation of a normal-sized autophagosome. The C-terminal half of mammalian Atg14 contains the Barkor/Atg14(L) autophagosome-targeting sequence (BATS) domain that preferentially binds to the highly curved membranes containing PtdIns(3)P and is proposed to target the PtdIns 3-kinase complex efficiently to the isolation membrane. Thus, the N- and C-terminal halves of Atg14 are likely to have an essential core function and a regulatory role, respectively. Copyright © 2011 Keisuke Obara and Yoshinori Ohsumi.

Kameya Y.,IHI Corporation | Hanamura K.,Tokyo Institute of Technology
Solar Energy | Year: 2011

The radiation absorption characteristics of a Ni nanoparticle suspension were investigated by spectroscopic transmission measurement. It was demonstrated that the absorption coefficient of the nanoparticle suspension is much higher than that of the base liquid for visible to near-infrared wavelengths. Radiation characteristics predicted by the Mie theory showed good agreement with the increase of absorption coefficient in wavelengths where the base liquid is transparent. It was also confirmed that a new transmittance measurement technique for a liquid sample using a liquid cell with no spacer was quite useful for evaluating a material possessing an extremely strong absorption band. The proposed measurement method and successive Kramers-Kronig analysis were validated by measuring the optical properties of water. The measurement and prediction process of the thermal radiation properties of nanoparticle suspensions developed here could be used in developing direct absorption solar collectors. © 2010 Elsevier Ltd.

Chun Y.N.,Chosun University | Kim S.C.,Chosun University | Yoshikawa K.,Tokyo Institute of Technology
Applied Energy | Year: 2011

A pyrolysis gasifier, with carbonization and activation steps, was developed to convert dried sludge into activated char and gas fuel energy. To determine the optimal driving conditions, parametric investigations were conducted on the amount of steam input, pyrolysis gasifier temperature and moisture content in the dried sludge.The optimal conditions for the dried sludge were found to be a steam input of 10. mL/min, gasifier temperature of 820°C and moisture content of 11% with a holding time in the pyrolysis gasifier of 1. h.The specific area of the activated char was 40.1m2/g, with an average pore diameter and volume of 63.49Å and 0.2354cm3/g, respectively. The pyrolysis gases were H2 (34.1%), CO (18.6%), CH4 (8.5%) and CO2 (8%). The higher heating value for the pyrolysis gas was 10,107kJ/Nm3. To determine the tar adsorption characteristics, a benzene adsorption test was conducted using a fixed bed adsorption tower (H/D=2, GHSV=1175/h). The saturation point of the activated char was found after 45min, and the amount of adsorption was 140mg/g.Therefore, the pyrolysis gasification of sewage sludge can produce activated char which can be used to reduce tar, and gasification gas which can be utilized as a high enthalpy gas fuel. © 2010 Elsevier Ltd.

Maeda K.,Tokyo Institute of Technology | Maeda K.,Japan Science and Technology Agency | Domen K.,University of Tokyo
Angewandte Chemie - International Edition | Year: 2012

Tripping the light fantastic: Despite small band gap energies (1.7-1.8 eV), BaZrO3-BaTaO2N solid solutions (Zr/Ta<0.1) are capable of photocatalyzing both water oxidation and reduction even under irradiation above 660 nm. Solar water splitting to form H2 and O2 was also demonstrated using a photoelectrochemical cell consisting of a BaZrO 2N solid solution as an anode and a Pt wire cathode. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Onaka S.,Tokyo Institute of Technology
Symmetry | Year: 2012

Using an x-y-z coordinate system, the equations of the superspheres have been extended to describe intermediate shapes between a sphere and various convex polyhedra. Near-polyhedral shapes composed of {100}, {111} and {110} surfaces with round edges are treated in the present study, where {100}, {111} and {110} are the Miller indices of crystals with cubic structures. The three parameters p, a and b are included to describe the {100}-{111}-{110} near-polyhedral shapes, where p describes the degree to which the shape is a polyhedron and a and b determine the ratios of the {100}, {111} and {110} surfaces. © 2012 by the authors; licensee MDPI, Basel, Switzerland.

Ando T.,Tokyo Institute of Technology
Physica E: Low-Dimensional Systems and Nanostructures | Year: 2011

A brief review is given on recent theoretical study on continuum models of optical phonons as well as zone-boundary phonons and effects of electronphonon interaction in monolayer and bilayer graphene, resulting in strong dependence of the frequency and broadening on the electron density. © 2010 ElsevierB.V. All rights reserved.

Hamura T.,Kwansei Gakuin University | Chuda Y.,Kwansei Gakuin University | Nakatsuji Y.,Kwansei Gakuin University | Suzuki K.,Tokyo Institute of Technology
Angewandte Chemie - International Edition | Year: 2012

A fair exchange: In the title reaction, alkynyllithium serves as an initiator for benzyne generation through an iodine-lithium exchange (see scheme; Tf=trifluoromethanesulfonyl). When performed in the presence of stoichiometric amounts of a nucleophile, the generated benzyne undergoes attack by lithio nucleophiles to generate aryllithium, which is then iodinated by iodoalkyne to give the iodoarenes 1. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Yardimci H.,Harvard University | Loveland A.B.,Harvard University | Habuchi S.,Tokyo Institute of Technology | Van Oijen A.M.,Harvard University | Walter J.C.,Harvard University
Molecular Cell | Year: 2010

The duplication of eukaryotic genomes involves the replication of DNA from multiple origins of replication. In S phase, two sister replisomes assemble at each active origin, and they replicate DNA in opposite directions. Little is known about the functional relationship between sister replisomes. Some data imply that they travel away from one another and thus function independently. Alternatively, sister replisomes may form a stationary, functional unit that draws parental DNA toward itself. If this "double replisome" model is correct, a constrained DNA molecule should not undergo replication. To test this prediction, lambda DNA was stretched and immobilized at both ends within a microfluidic flow cell. Upon exposure to Xenopus egg extracts, this DNA underwent extensive replication by a single pair of diverging replisomes. The data show that there is no obligatory coupling between sister replisomes and, together with other studies, imply that genome duplication involves autonomously functioning replisomes. © 2010 Elsevier Inc.

Kashino M.,Nippon Telegraph and Telephone | Kashino M.,Tokyo Institute of Technology | Kondo H.M.,Nippon Telegraph and Telephone
Philosophical Transactions of the Royal Society B: Biological Sciences | Year: 2012

Recent studies have shown that auditory scene analysis involves distributed neural sites below, in, and beyond the auditory cortex (AC). However, it remains unclear what role each site plays and how they interact in the formation and selection of auditory percepts. We addressed this issue through perceptual multistability phenomena, namely, spontaneous perceptual switching in auditory streaming (AS) for a sequence of repeated triplet tones, and perceptual changes for a repeated word, known as verbal transformations (VTs). An event-related fMRI analysis revealed brain activity timelocked to perceptual switching in the cerebellum for AS, in frontal areas for VT, and the AC and thalamus for both. The results suggest that motor-based prediction, produced by neural networks outside the auditory system, plays essential roles in the segmentation of acoustic sequences both in AS and VT. The frequency of perceptual switching was determined by a balance between the activation of two sites, which are proposed to be involved in exploring novel perceptual organization and stabilizing current perceptual organization. The effect of the gene polymorphism of catechol-O-methyltransferase (COMT) on individual variations in switching frequency suggests that the balance of exploration and stabilization is modulated by catecholamines such as dopamine and noradrenalin. These mechanisms would support the noteworthy flexibility of auditory scene analysis. copy; 2012 The Royal Society.

Saikawa K.,University of Tokyo | Yamaguchi M.,Tokyo Institute of Technology
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2013

We discuss the possibility that dark matter axions form a Bose-Einstein condensate (BEC) due to the gravitational self interactions. The formation of BEC occurs in the condensed regime, where the transition rate between different momentum states is large compared to the energy exchanged in the transition. The time evolution of the quantum state occupation number of axions in the condensed regime is derived based on the in-in formalism. We recover the expression for the thermalization rate due to self interaction of the axion field, which was obtained in the other literature. It is also found that the leading order contributions for interactions between axions and other species vanish, which implies that the axion BEC does not give any significant modifications on standard cosmological parameters. © 2013 American Physical Society.

Huenteler J.,ETH Zurich | Schmidt T.S.,ETH Zurich | Kanie N.,Tokyo Institute of Technology
Energy Policy | Year: 2012

The Japanese electricity sector is facing serious challenges in the aftermath of the Fukushima nuclear disaster. The government has responded to the crisis with a new feed-in-tariff to promote increased utilization of renewable energy, and proposed to reduce the dependence on nuclear power. In this viewpoint, we liken the transition implied by recently updated goals for the diffusion of renewables in Japan to the transition in Germany in the last decade. We argue that some of the lessons learned in Germany might prove valuable for the steps Japan considers taking. In particular, we focus on the new Japanese feed-in tariff for solar photovoltaics. In view of the recent developments in Germany, we emphasize the importance of the scheme's political legitimacy, which needs to be maintained through adequate design of both policy instrument and political process. We conclude with policy implications and a targeted research agenda. © 2012 Elsevier Ltd.

Hiki Y.,Tokyo Institute of Technology
Journal of Non-Crystalline Solids | Year: 2011

Viscosity in pure shear deformation mode was measured for various glasses. The temperature dependence of viscosity was of hydrodynamic (Vogel-Tammann- Fulcher) type and of the hopping (Arrhenius) type above and below the glass transition temperature. Double Arrhenius dependence was seen in glasses containing molecular chains. Internal friction was measured near and above the glass transition for metallic and polymer glasses. The viscoelastic relaxation was observed and the result was analyzed by adopting the Maxwell model and the Maxwell relation. In the relaxation a correlation between the pre-exponential factor and the activation energy (compensation effect) was seen. Ultrasound and Brillouin scattering experiments were performed for a polymer glass. Relaxation was seen near the glass transition in the sound velocity and sound attenuation. The activation energy values for the relaxation obtained by various experiments were compared by adopting the idea of potential energy landscape. © 2010 Elsevier B.V.All rights reserved.

Tsuchiya H.,Tokyo Institute of Technology
Renewable Energy | Year: 2012

This paper reports on the national renewable electricity supply provided largely by solar photovoltaics and wind power, together with hydro, geothermal and biomass, in Japan. The preliminary statistical analysis of the Japanese data shows that the optimal mix to minimise the standard deviation of mismatch and the theoretical energy storage capacity is a combination of 75% solar and 25% wind power. Dynamic simulations were performed to calculate the electricity supply with hourly weather data regarding solar radiation and wind speed for the electricity demand in a target year approximately 2050. Simulations with different parameters reveal the relationships between energy storage, excess energy and back-up energy. The results show that the optimal mix is the same as that proposed by a statistical study and that the necessary electricity storage capacity is five times that of pumped storage hydro today. © 2012 Elsevier Ltd.

Yamamoto T.,Tokyo Institute of Technology | Fujii T.,University of Tokyo
Nanotechnology | Year: 2010

Separation and separation-based analysis of biomolecules are fundamentally important techniques in the field of biotechnology. These techniques, however, depend on stochastic processes that intrinsically involve uncertainty, and thus it is not possible to achieve 100% separation accuracy. Theoretically, the ultimate resolution and sensitivity should be realized in a single-molecule system because of the deterministic nature of single-molecule manipulation. Here, we have proposed and experimentally demonstrated the concept of a 'single-molecule sorter' that detects and correctly identifies individual single molecules, realizing the ultimate level of resolution and sensitivity for any separation-based technology. The single-molecule sorter was created using a nanofluidic network consisting of a single inlet channel that branches off into multiple outlet channels. It includes two major functional elements, namely a single-molecule detection and identification element and a flow path switching element to accurately separate single molecules. With this system we have successfully demonstrated the world's first single-molecule sorting using DNA as a sample molecule. In the future, we hope to expand the application of such devices to comprehensive sorting of single-proteins from a single cell. We also believe that in addition to the single-molecule sorting method reported here, other types of single-molecule based processes will emerge and find use in a wide variety of applications. © 2010 IOP Publishing Ltd.

Takezoe H.,Tokyo Institute of Technology
Topics in Current Chemistry | Year: 2012

It is well known that spontaneous deracemization or spontaneous chiral resolution occasionally occurs when racemic molecules are crystallized. However, it is not easy to believe such phenomenon will occur when forming liquid crystal phases. Spontaneous chiral domain formation is introduced, when molecules form particular liquid crystal phases. Such molecules possess no chiral carbon but may have axial chirality. However, the potential barrier between two chiral states is low enough to allow mutual transformation even at room temperature. Therefore the systems are essentially not racemic but nonchiral or achiral. First, enhanced chirality by doping chiral nematic liquid crystals with nonchiral molecules is described. Emphasis is made on ester molecules for their anomalous behavior. Second, spontaneous chiral resolution is discussed. Three examples with rod-, bent-, and disk-shaped molecules are shown to give such phenomena. Particular attention will be paid to controlling enantiomeric excess (ee). Actually, almost 100% ee was obtained by applying some external chiral stimuli. This is very noteworthy in the sense that we can create chiral molecules (chiral field) without using any chiral species. © 2011 Springer-Verlag Berlin-Heidelberg.

Ayoub N.,Helwan University | Yuji N.,Tokyo Institute of Technology
Energy Policy | Year: 2012

Almost all countries have issued laws and regulations to promote renewable energy (RE). However, the applications and motivations of such laws as well as achievements have been different. Currently, the Japanese government has announced its targets to expand the electricity feed-in tariff scheme for solar power, along with other energy sources, within two years to meet the goal set by the Japanese Prime Minister who, in the 15th United Nations Climate Change Conference (COP15) held in September 2009, proclaimed to cut 25% of greenhouse gas (GHG) emissions from the 1990 levels by 2020. In this paper, the current Japanese energy policies and measures for promoting RE in comparison to popular methods followed worldwide are explored. Furthermore, a Least Cost Feed-in Tariff (LCFIT) Simulation Model for Japanese case was developed to calculate the optimal mix of technologies to reach certain targets. The LCFIT also calculates the tariff that should be proposed for each technology and the total cost for the program with and without a carbon tax and estimates the premium added to the bill of the customer every month. © 2012 Elsevier Ltd.

Maeda K.,University of Tokyo | Higashi M.,Hokkaido University | Lu D.,Tokyo Institute of Technology | Abe R.,Hokkaido University | Domen K.,University of Tokyo
Journal of the American Chemical Society | Year: 2010

A two-step photocatalytic water splitting (Z-scheme) system consisting of a modified ZrO2/TaON species (H2 evolution photocatalyst), an O2 evolution photocatalyst, and a reversible donor/acceptor pair (i.e., redox mediator) was investigated. Among the O2 evolution photocatalysts and redox mediators examined, Pt-loaded WO3 (Pt/WO3) and the IO3-/I- pair were respectively found to be the most active components. Combining these two components with Pt-loaded ZrO2/TaON achieved stoichiometric water splitting into H2 and O2 under visible light, achieving an apparent quantum yield of 6.3% under irradiation by 420.5 nm monochromatic light under optimal conditions, 6 times greater than the yield achieved using a TaON analogue. To the best of our knowledge, this is the highest reported value to date for a nonsacrificial visible-light-driven water splitting system. The high activity of this system is due to the efficient reaction of electron donors (I- ions) and acceptors (IO3- ions) on the Pt/ZrO2/TaON and Pt/WO3 photocatalysts, respectively, which suppresses undesirable reverse reactions involving the redox couple that would otherwise occur on the photocatalysts. Photoluminescence and photoelectrochemical measurements indicated that the high activity of this Z-scheme system results from the moderated n-type semiconducting character of ZrO2/TaON, which results in a lower probability of undesirable electron-hole recombination in ZrO2/TaON than in TaON. © 2010 American Chemical Society.

Mikami K.,Tokyo Institute of Technology | Tomita Y.,University of Tokyo | Itoh Y.,University of Tokyo
Angewandte Chemie - International Edition | Year: 2010

(Figure Presented) The l's have it: A conceptually new C-F activation/C-C formation and its mechanism are described. Surprisingly, a reaction with Li-enolates and trifluoromethyl iodide gave (alpha)-difluoromethyl product via C-F bond cleavage in preference to the weaker C-I bond of trifluoromethyliodide. This reaction proceeds without the use of any late transitionmetal catalyst (see scheme; LHMDS = lithium hexamethyldlsilaxide). © 2010 Wiley-VCH Verlag GmbH & Co. KGaA.

Miyoshi Y.,Nagoya University | Kataoka R.,Tokyo Institute of Technology
Journal of Atmospheric and Solar-Terrestrial Physics | Year: 2011

The outer radiation belt shows solar cycle variation: the L-shell of the electron flux peak in the outer belt shifts inward during the period between the rising phase and the solar maximum, while it shifts outward between the beginning of the declining phase and the solar minimum. We show a possible mechanism which considers two typical types of magnetic storms categorized in accordance with solar wind drivers, namely coronal mass ejections (CMEs) and corotating interaction regions (CIRs). Large flux enhancements at the inner portion of the outer belt tend to occur during the recovery phase of great storms driven by CMEs, while large flux enhancements at the outer portion and at geosynchronous orbit tend to occur during the recovery phase of relatively moderate storms driven by CIRs. High-speed coronal hole streams which do not always cause large magnetic storms also effectively enhance the electron flux enhancement at the outer portion and in geosynchronous orbit. In this framework, the plasmapause always plays an important role in both flux enhancement and flux loss in the outer belt. The average plasmapause position depends on the storm amplitude, and the plasmapause reaches closest to the Earth during great storms driven by CMEs. CMEs themselves and CME-driven storms occur during maximum periods of solar activity, while CIRs themselves and CIR-driven storms occur during the solar declining phase. The observed long-term variations of the outer belt can therefore be understood in terms of their dependence on the large-scale interplanetary structures, varying depending on the phase of the solar cycle. © 2010 Elsevier Ltd.

Ikariya T.,Tokyo Institute of Technology
Topics in Organometallic Chemistry | Year: 2011

The discovery and development of conceptually new chiral bifunctional molecular catalysts based on the metal/NH acid-base synergy effect are described. The chiral bifunctional molecular catalysis originally developed for asymmetric transfer hydrogenation of ketones is applicable in enantioselective hydrogenation of polar functionalities as well as practical oxidative reactions including aerobic oxidation of alcohols. The structural modification and electronic fine-tuning of the protic amine chelating ligands are crucial to develop unprecedented catalytic reactions. The present bifunctional transition metal-based molecular catalyst offers a great opportunity to open up new fundamentals for stereoselective molecular transformations. © 2011 Springer-Verlag Berlin Heidelberg.

Hoffmann R.W.,University of Marburg | Suzuki K.,Tokyo Institute of Technology
Angewandte Chemie - International Edition | Year: 2013

Fundamental aspects of chemically activated reactive intermediates can possibly be learned from the novel generation of arynes. The intramolecular [4+2] cycloaddition between a diyne and an (electronically activated) alkyne also provides a new route to generate arynes (see scheme). Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Sueyoshi T.,New Mexico Institute of Mining and Technology | Goto M.,Tokyo Institute of Technology
Energy Economics | Year: 2015

This study discusses a new use of DEA (Data Envelopment Analysis) environmental assessment to measure unified (operational and environmental) and scale efficiencies among inputs, desirable and undesirable outputs. In particular, the measurement of scale efficiency is discussed by two non-radial models. That is a new methodological contribution. To discuss these efficiency measures, this study first examines a concept of disposability from the perspective of corporate strategies to adapt a regulation change on undesirable outputs. The concept is separated into natural and managerial disposability. After discussing how to measure the degree of scale efficiency within the non-radial approach, this study applies the proposed DEA environmental assessment to measure the performance of coal-fired power plants in the U.S. north-east region. The region has been long producing a large amount of coal from the Appalachian Mountains. The coal mining industry has supported U.S. energy utility and other industries. Because of the long history, the quality of coal became worse and the coal-fired power plants have been producing a large amount of undesirable gases. This study has statistically confirmed that there is a significant difference between the two types (BIT: bituminous coal and SUB: subbituminous coal) of coal-fired power plants in terms of their unified efficiency measures, including their scale efficiencies, under the concept of managerial disposability (the first priority: environment performance and the second priority: operational performance). In contrast, under the natural disposability (the first priority: operational performance and the second priority: environmental performance), this study cannot find such a statistical significance between them. The fact, in which BIT outperforms SUB in terms of their unified and scale efficiencies, suggests the policy implication that these power plants need to shift their coal combustions from SUB to BIT in the United States. Besides the empirical finding, this study cannot confirm the other hypothesis on whether coal-fired power plants with small operation (less than 50% in plant capacity factor) outperform ones with large operation (more than 50% in plant capacity factor), and vice versa, in terms of their unified and scale efficiency measures under natural and managerial disposability. An exception is found in environmental performance under variable returns to scale. The rationale is because their plant operations are frequently monitored by regulatory agencies. As a consequence, this study cannot find such a statistical difference between them on operational performance. This result implies that the regulation on coal-fired power plants has been effective on their unified performance but large power plants may have a potential to improve their environmental performance. © 2015 Elsevier B.V.

Sahoo B.K.,Physical Research Laboratory | Das B.P.,Tokyo Institute of Technology
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2015

Lifetimes of the 6dD3/22 and 6dD5/22 states in Fr are determined from calculations of the radiative transition amplitudes of the allowed electric dipole (E1) and the forbidden electric quadrupole (E2) and magnetic dipole (M1) channels which were performed using the second-order many-body perturbation theory and the coupled-cluster method at different levels of approximations in the relativistic framework. The values obtained for these two quantities are 540(10) and 1704(32) ns, respectively. These relatively long lifetimes and the large electric dipole parity-non-conserving amplitudes of 7sS1/22→6dD3/2,5/22 transitions strongly favor Fr as a leading candidate for the measurement of parity nonconservation arising from the neutral-current weak interaction and the nuclear anapole moment. In another important application, these 6D states in Fr can be used efficiently for resonance ionization spectroscopic techniques to carry out precise measurements of the properties of the higher excited states due to the long lifetimes of these states. © 2015 American Physical Society.

Tatsumi S.,Tokyo University of Science | Tatsumi S.,Tokyo Institute of Technology | Aso S.,Tokyo University of Science | Yamamuro O.,Tokyo University of Science
Physical Review Letters | Year: 2012

We have obtained some universal thermodynamic properties on glass transitions of molecular liquids. The heat capacity C p of glassy propene, which was vitrified by using a vapor-deposition technique, was measured with a newly developed adiabatic calorimeter. Propene has the lowest glass transition temperature (T g=56K), the largest C p jump at T g (Cplq/Cpgl∼2.5), and the lowest residual entropy (S res∼Rln2) compared with glass-forming molecules measured before. We have analyzed the present data with other hydrocarbon molecules vitrified by liquid quenching and obtained the following results: (1) The excess heat capacities are scaled well by using a Kauzmann temperature T K, (2) The size of the cooperative rearrangement region (CRR) frozen at T g increases with decreasing the temperature difference between T g and T K (Kauzmann temperature), and (3) The simpler the molecule is, the larger the frozen CRR becomes. These are all supporting the validity of the Adam-Gibbs theory. © 2012 American Physical Society.

Takeuchi D.,Tokyo Institute of Technology
Polymer Journal | Year: 2012

Pd complexes with diimine ligands promoted the controlled cyclopolymerization of 1,6-dienes and 1,6,11-trienes to afford polymers containing 1,2-trans-cyclopentane groups with well-regulated stereochemistry. The polymerization proceeded with quantitative cyclization of the monomer, even under bulk conditions or in copolymerization reactions with ethylene and α-olefins. The polymerization of monomers with oligomethylene spacers yielded polymers with five-membered rings that are accurately distributed along the polymer chain. 4-Alkylcyclopentenes and alkenylcyclohexanes were also polymerized by Pd-diimine complexes to afford polymers with 1,3-trans- cyclopentane groups and 1,4-trans-cyclohexane groups, respectively. Pd complexes with a C 2 symmetrical structure promoted the isospecific polymerization of 4-alkylcyclopentenes, and the resultant isotactic polymers showed liquid crystalline properties. The mechanism of the polymerization reaction has been revealed. © 2012 The Society of Polymer Science, Japan (SPSJ) All rights reserved.

Tezuka Y.,Tokyo Institute of Technology
Polymer Journal | Year: 2012

The geometrical conception and current synthetic challenges of topological polymer chemistry have been reviewed. On the basis of the systematic classification and isomeric properties of polymer chain topologies, a variety of novel multicyclic macromolecular constructions have now been rationally designed and subsequently realized by intriguing synthetic protocols. In particular, cyclic and multicyclic polymer products are effectively produced by an electrostatic polymer self-assembly of telechelic precursors that contain cyclic ammonium salt groups accompanying polyfunctional carboxylate counteranions and the subsequent covalent conversion through the ring-opening or through the ring-emitting reaction of the cyclic ammonium salt groups by carboxylate counteranions (Electrostatic Self-assembly and Covalent Fixation (ESA-CF) process). Furthermore, the ESA-CF process, in conjunction with effective linking/cleaving chemistry (including the metathesis condensation (clip) and alkyne-azide addition (click) reactions), has been demonstrated as a new synthetic protocol for unprecedented multicyclic macromolecular topologies. © 2012 The Society of Polymer Science.

Kokubo E.,Japan National Astronomical Observatory | Genda H.,Tokyo Institute of Technology
Astrophysical Journal Letters | Year: 2010

The final stage of terrestrial planet formation is known as the giant impact stage where protoplanets collide with one another to form planets. So far this stage has been mainly investigated by N-body simulations with an assumption of perfect accretion in which all collisions lead to accretion. However, this assumption breaks for collisions with high velocity and/or a large impact parameter. We derive an accretion condition for protoplanet collisions in terms of impact velocity and angle and masses of colliding bodies, from the results of numerical collision experiments. For the first time, we adopt this realistic accretion condition in N-body simulations of terrestrial planet formation from protoplanets. We compare the results with those with perfect accretion and show how the accretion condition affects terrestrial planet formation. We find that in the realistic accretion model about half of collisions do not lead to accretion. However, the final number, mass, orbital elements, and even growth timescale of planets are barely affected by the accretion condition. For the standard protoplanetary disk model, typically two Earth-sized planets form in the terrestrial planet region over about 10 8 yr in both realistic and perfect accretion models. We also find that for the realistic accretion model, the spin angular velocity is about 30% smaller than that for the perfect accretion model, which is as large as the critical spin angular velocity for rotational instability. The spin angular velocity and obliquity obey Gaussian and isotropic distributions, respectively, independently of the accretion condition. © 2010. The American Astronomical Society.

Iwamoto M.,Tokyo Institute of Technology
Catalysis Today | Year: 2015

The conversion of ethanol to propene were examined on Ni ion-loaded silica MCM-41(Ni-M41), Sc-modified In2O3 (Sc/In2O3), and a solid solution of Y2O3-CeO2. The propene production activity was in the order, Sc/In2O3 > Y2O3-CeO2 > Ni-M41, while their stability during the reaction was Y2O3-CeO2 ∼ Sc/In2O3 > Ni-M41. The propene yield and durability of Sc/In2O3 were greatly improved by addition of water and hydrogen in the reactant stream. The reaction mechanism was greatly dependent on the catalyst employed. On Ni-M41, the metathesis reaction of ethene and butenes, produced through dimerization of ethene, was a key step for the propene formation. On the remaining two oxide catalysts, the major pathways were the common: ethanol → acetaldehyde → acetone → propene. The detailed reaction pathways, however, were different from each other. On Sc/In2O3, acetaldehyde was oxidized to acetic acid with water or a surface hydroxyl group and the resulting acetic acid was converted to acetone and carbon dioxide through ketonization. On the other hand, on Y2O3-CeO2, acetaldehyde was converted to ethyl acetate, and then it decomposed to form acetic acid and ethene. Acetic acid was converted to acetone and carbon dioxide in the same manner as that on Sc/In2O3. The by-production of much amounts of ethene was characteristic on Y2O3-CeO2. On the Sc/In2O3 oxide, a hydrogen molecule was active for the hydrogenation of acetone to 2-propanol. In contrast, on the Y2O3-CeO2 oxide, hydrogenation of acetone did not proceed with hydrogen but did with the co-fed ethanol, that is, by the Meerwein-Ponndorf-Verley reduction. © 2014 Elsevier B.V. All rights reserved.

Tajima R.,Tokyo Institute of Technology | Fischer T.B.,University of Liverpool
Environmental Impact Assessment Review | Year: 2013

This paper aims at providing empirical evidence to the question as to whether integration of different instruments is achieving its aim in supporting sustainable decision making, focusing on SEA inclusive sustainability appraisal (SA) and other impact assessments (IAs) currently used in English spatial planning. Usage of IAs in addition to SA is established and an analysis of the integration approach (in terms of process, output, and assessor) as well as its effectiveness is conducted. It is found that while integration enhances effectiveness to some extent, too much integration, especially in terms of the procedural element, appears to diminish the overall effectiveness of each IA in influencing decisions as they become captured by the balancing function of SA. © 2013 Elsevier Inc.

Susa Y.,Tokyo Institute of Technology | Tanaka S.,Keio University
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2015

We study the detection capability of the weak-value amplification on the basis of the statistical hypothesis testing. We propose a reasonable testing method in the physical and statistical senses to find that the weak measurement with the large weak value has the advantage to increase the detection power and to reduce the possibility of missing the presence of interaction. We enhance the physical understanding of the weak value and mathematically establish the significance of the weak-value amplification. Our present work overcomes the critical dilemma of the weak-value amplification that the larger the amplification is, the smaller the number of data becomes, because the statistical hypothesis testing works even for a small number of data. This is contrasted with the parameter estimation by the weak-value amplification in the literature which requires a large number of data. © 2015 American Physical Society. ©2015 American Physical Society.

Tazaki R.,Kyoto University | Nomura H.,Tokyo Institute of Technology
Astrophysical Journal | Year: 2015

We study the dust motion at the surface layer of protoplanetary disks. Dust grains in the surface layer migrate outward owing to angular momentum transport via gas-drag force induced by the stellar radiation pressure. In this study we calculate the mass flux of the outward motion of compact grains and porous dust aggregates by the radiation pressure. The radiation pressure force for porous dust aggregates is calculated using the T-Matrix Method for the Clusters of Spheres. First, we confirm that porous dust aggregates are forced by strong radiation pressure even if they grow to be larger aggregates, in contrast to homogeneous and spherical compact grains, for which radiation pressure efficiency becomes lower when their sizes increase. In addition, we find that the outward mass flux of porous dust aggregates with monomer size of 0.1 μm is larger than that of compact grains by an order of magnitude at the disk radius of 1 AU, when their sizes are several microns. This implies that large compact grains like calcium-aluminum-rich inclusions are hardly transported to the outer region by stellar radiation pressure, whereas porous dust aggregates like chondritic-porous interplanetary dust particles are efficiently transported to the comet formation region. Crystalline silicates are possibly transported in porous dust aggregates by stellar radiation pressure from the inner hot region to the outer cold cometary region in the protosolar nebula. © 2015. The American Astronomical Society. All rights reserved.

The Hencky strain is a logarithmic strain extended to a three-dimensional analysis. Although Onaka has shown that the Hencky equivalent strain is an appropriate measure of large simple-shear deformation (2010), Jonas et al. (2011) have recently presented a paper claiming that the application of the Hencky strain to large simple-shear deformation is in error. In the present paper, it is shown that the claim of Jonas et al. is contrary to recent accepted knowledge on the Hencky strain. © 2012 The Japan Institute of Metals.

Yokoyama T.,Tokyo Institute of Technology
Physical Review B - Condensed Matter and Materials Physics | Year: 2012

We investigate Josephson and proximity effects on the surface of a topological insulator on which superconductors and a ferromagnet are deposited. The superconducting regions are described by the conventional BCS Hamiltonian, rather than the superconducting Dirac Hamiltonian. Junction interfaces are assumed to be dirty. We obtain analytical expressions of the Josephson current and the proximity-induced anomalous Green's function on the topological insulator. The dependence of the Josephson effect on the junction length, the temperature, the chemical potential, and the magnetization is discussed. It is also shown that the proximity-induced pairing on the surface of a topological insulator includes even- and odd-frequency triplet pairings as well as a conventional s-wave pairing. © 2012 American Physical Society.

Kajihara M.,Tokyo Institute of Technology
Materials Transactions | Year: 2012

If a binary Fe-C alloy with a single-phase microstructure of the austenitic γ phase is isothermally annealed in an appropriate decarburization atmosphere, a layer of the ferritic α phase is formed on the surface of the γ phase and gradually grows into the γ phase. The kinetics for the growth of the α layer during the decarburization was quantitatively analyzed using a diffusion model at annealing temperatures between 1011 and 1185K. In the analysis, the diffusion coefficient of C in each phase is considered independent of the chemical composition. According to the model, the square of the thickness l of the α layer is proportional to the annealing time t as described by the relationship l 2 = Kt. This relationship is called the parabolic relationship. As the initial concentration x γ0 of C in the γ phase increases from the minimum value to the maximum value for the γ single-phase region at each annealing temperature T, the parabolic coefficient K monotonically decreases from the maximum value K max d to the minimum value K min d. As T decreases, K max d decreases, but K min d increases. However, both K max d and K min d vary depending on T in a complicated manner. Thus, an Arrhenius equation is not applicable even to the temperature dependence of K max d in the whole annealing temperature range. At a constant value of x γ0, K monotonically decreases with increasing value of T. This means that the growth of the α layer takes place faster at lower annealing temperatures than at higher annealing temperatures. Such temperature dependence of the kinetics coincides well with experimental observations. © 2012 The Japan Institute of Metals.

Fujii M.S.,Leiden University | Saitoh T.R.,Tokyo Institute of Technology | Portegies Zwart S.F.,Leiden University
Astrophysical Journal | Year: 2012

Young star clusters such as NGC3603 and Westerlund 1 and 2 in the Milky Way and R136 in the Large Magellanic Cloud are dynamically more evolved than expected based on their current relaxation times. In particular, the combination of a high degree of mass segregation, a relatively low central density, and the large number of massive runaway stars in their vicinity are hard to explain with the monolithic formation of these clusters. Young star clusters can achieve such a mature dynamical state if they formed through the mergers of a number of less massive clusters. The shorter relaxation times of less massive clusters cause them to dynamically evolve further by the time they merge, and the merger product preserves the memory of the dynamical evolution of its constituent clusters. With a series of N-body simulations, we study the dynamical evolution of single massive clusters and those that are assembled through merging smaller clusters together. We find that the formation of massive star clusters through the mergers of smaller clusters can reproduce the currently observed spatial distribution of massive stars, the density, and the characteristics (number and mass distribution) of the stars ejected as runaways from young dense clusters. We therefore conclude that these clusters and possibly other young massive star clusters formed through the mergers of smaller clusters. © 2012 The American Astronomical Society. All rights reserved.

Genda H.,University of Tokyo | Kokubo E.,Japan National Astronomical Observatory | Ida S.,Tokyo Institute of Technology
Astrophysical Journal | Year: 2012

At the final stage of terrestrial planet formation, known as the giant impact stage, a few tens of Mars-sized protoplanets collide with one another to form terrestrial planets. Almost all previous studies on the orbital and accretional evolution of protoplanets in this stage have been based on the assumption of perfect accretion, where two colliding protoplanets always merge. However, recent impact simulations have shown that collisions among protoplanets are not always merging events, that is, two colliding protoplanets sometimes move apart after the collision (hit-and-run collision). As a first step toward studying the effects of such imperfect accretion of protoplanets on terrestrial planet formation, we investigated the merging criteria for collisions of rocky protoplanets. Using the smoothed particle hydrodynamic method, we performed more than 1000 simulations of giant impacts with various parameter sets, such as the mass ratio of protoplanets, γ, the total mass of two protoplanets, M T, the impact angle, θ, and the impact velocity, v imp. We investigated the critical impact velocity, v cr, at the transition between merging and hit-and-run collisions. We found that the normalized critical impact velocity, v cr/v esc, depends on γ and θ, but does not depend on M T, where v esc is the two-body escape velocity. We derived a simple formula for v cr/v esc as a function of γ and θ (Equation (16)), and applied it to the giant impact events obtained by N-body calculations in the previous studies. We found that 40% of these events should not be merging events. © 2012. The American Astronomical Society. All rights reserved.

Okuzumi S.,Tokyo Institute of Technology | Okuzumi S.,Nagoya University | Ormel C.W.,University of California at Berkeley
Astrophysical Journal | Year: 2013

Turbulence in protoplanetary disks affects planet formation in many ways. While small dust particles are mainly affected by the aerodynamical coupling with turbulent gas velocity fields, planetesimals and larger bodies are more affected by gravitational interaction with gas density fluctuations. For the latter process, a number of numerical simulations have been performed in recent years, but a fully parameter-independent understanding has not been yet established. In this study, we present simple scaling relations for the planetesimal stirring rate in turbulence driven by magnetorotational instability (MRI), taking into account the stabilization of MRI due to ohmic resistivity. We begin with order-of-magnitude estimates of the turbulence-induced gravitational force acting on solid bodies and associated diffusion coefficients for their orbital elements. We then test the predicted scaling relations using the results of recent ohmic-resistive MHD simulations by Gressel et al. We find that these relations successfully explain the simulation results if we properly fix order-of-unity uncertainties within the estimates. We also update the saturation predictor for the density fluctuation amplitude in MRI-driven turbulence originally proposed by Okuzumi & Hirose. Combination of the scaling relations and saturation predictor allows us to know how the turbulent stirring rate of planetesimals depends on disk parameters such as the gas column density, distance from the central star, vertical resistivity distribution, and net vertical magnetic flux. In Paper II, we apply our recipe to planetesimal accretion to discuss its viability in turbulent disks. © 2013. The American Astronomical Society. All rights reserved.

Ogihara M.,Nagoya University | Ida S.,Tokyo Institute of Technology
Astrophysical Journal | Year: 2012

As the number of discovered extrasolar planets has been increasing, diversity of planetary systems requires studies of new formation scenarios. It is important to study satellite formation in circumplanetary disks, which is often viewed as analogous to formation of rocky planets in protoplanetary disks. We investigated satellite formation from satellitesimals around giant planets through N-body simulations that include gravitational interactions with a circumplanetary gas disk. Our main aim is to reproduce the observable properties of the Galilean satellites around Jupiter through numerical simulations, as previous N-body simulations have not explained the origin of the resonant configuration. We performed accretion simulations based on the work of Sasaki et al., in which an inner cavity is added to the model of Canup & Ward. We found that several satellites are formed and captured in mutual mean motion resonances outside the disk inner edge and are stable after rapid disk gas dissipation, which explains the characteristics of the Galilean satellites. In addition, owing to the existence of the disk edge, a radial compositional gradient of the Galilean satellites can also be reproduced. An additional objective of this study is to discuss orbital properties of formed satellites for a wide range of conditions by considering large uncertainties in model parameters. Through numerical experiments and semianalytical arguments, we determined that if the inner edge of a disk is introduced, a Galilean-like configuration in which several satellites are captured into a 2:1 resonance outside the disk inner cavity is almost universal. In fact, such a configuration is produced even for a massive disk ≳ 104 g cm-2 and rapid type I migration. This result implies the inevitability of a Galilean satellite formation in addition to providing theoretical predictions for extrasolar satellites. That is, we can predict a substantial number of exomoon systems in the 2:1 mean motion resonance close to their host planets awaiting discovery. © 2012. The American Astronomical Society. All rights reserved.

Shyue K.-M.,National Taiwan University | Xiao F.,Tokyo Institute of Technology
Journal of Computational Physics | Year: 2014

We describe a novel interface-sharpening approach for efficient numerical resolution of a compressible homogeneous two-phase flow governed by a quasi-conservative five-equation model of Allaire et al. (2001) [1]. The algorithm uses a semi-discrete wave propagation method to find approximate solution of this model numerically. In the algorithm, in regions near the interfaces where two different fluid components are present within a cell, the THINC (Tangent of Hyperbola for INterface Capturing) scheme is used as a basis for the reconstruction of a sub-grid discontinuity of volume fractions at each cell edge, and it is complemented by a homogeneous-equilibrium-consistent technique that is derived to ensure a consistent modeling of the other interpolated physical variables in the model. In regions away from the interfaces where the flow is single phase, standard reconstruction scheme such as MUSCL or WENO can be used for obtaining high-order interpolated states. These reconstructions are then used as the initial data for Riemann problems, and the resulting fluctuations form the basis for the spatial discretization. Time integration of the algorithm is done by employing a strong stability-preserving Runge-Kutta method. Numerical results are shown for sample problems with the Mie-Grüneisen equation of state for characterizing the materials of interests in both one and two space dimensions that demonstrate the feasibility of the proposed method for interface-sharpening of compressible two-phase flow. To demonstrate the competitiveness of our approach, we have also included results obtained using the anti-diffusion interface sharpening method. © 2014 Elsevier Inc.

Fuchigami T.,Tokyo Institute of Technology
Biomatter | Year: 2012

Nano-sized FePt capsules with two types of ultrathin shell were fabricated using a template method for use in a nano-scale drug delivery system. One capsule was composed of an inorganic-organic hybrid shell of a water-soluble polymer and FePt nanoparticles, and the other capsule was composed of a network of fused FePt nanoparticles. We demonstrated that FePt nanoparticles selectively accumulated on the polymer molecules adsorbed on the template silica particles, and investigated the morphologies of the particle accumulation by changing the concentration of the polymer solution with which the template particles were treated. Capsular size was reduced from 340 to less than 90 nm by changing the size of the silica template particles, and the shell thickness was controlled by changing the amount of FePt nanoparticles adsorbed on the template particles. The hybrid shell was maintained by the connection of FePt nanoparticles and polymer molecules, and the shell thickness was 10 nm at the maximum. The FePt network shell was fabricated by hydrothermal treatment of the FePt/polymer-modified silica composite particles. The FePt network shell was produced from only the FePt alloy, and the shell thickness was 3 nm. Water-soluble anti-cancer drugs could be loaded into the hollow space of FePt network capsules, and lipid-coated FePt network capsules loaded with anti-cancer drugs showed cellular toxicity. The nano-sized capsular structure and the ultrathin shell suggest applicability as a drug carrier in magnetically guided drug delivery systems.

Sato S.,Toyota Central Research and Development Laboratories Inc. | Sato S.,Japan Science and Technology Agency | Morikawa T.,Toyota Central Research and Development Laboratories Inc. | Kajino T.,Toyota Central Research and Development Laboratories Inc. | Ishitani O.,Tokyo Institute of Technology
Angewandte Chemie - International Edition | Year: 2013

Mononuclear iridium(III) terpyridine (tpy) 2-phenylpyridine (ppy) complexes [Ir(tpy)(R-ppy)Cl] (R=H, Me, CF3) can act as efficient and selective CO2 reduction photocatalysts. The reaction is driven using visible light in a homogeneous solution, and even in a H2O mixed solution. The most efficient photocatalyst is [Ir(tpy)(Me-ppy)Cl], for which the turnover in CO was over 50 and the quantum yield was 0.21 at 480 nm. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Iwasaki Y.,Tokyo Institute of Technology | Ormerod S.J.,University of Cardiff
Environmental Pollution | Year: 2012

We derived safe concentrations (SCs) of copper, zinc, cadmium, and manganese using river macroinvertebrate surveys at over 400 individual sites on three continents represented by the UK, USA, and Japan. We related a standardized measure of EPT (Ephemeroptera, Plecoptera, and Trichoptera) taxon richness to dissolved metal concentrations and identified SCs as the thresholds at which effects became apparent. Estimated SCs (and 95% confidence interval, μg/L) for copper, zinc, cadmium, and manganese were 6.6 (1.2-14.2), 34 (11-307), 0.11 (0.06-0.49), and 7.1 (1.4-20.5), respectively. These values for copper, zinc, and cadmium overlapped closely with laboratory-derived SCs available from water quality criteria/standards in the USA/UK and also predicted no effect concentrations from European Union risk assessments. Such laboratory-derived SCs for manganese are unavailable. These results not only add considerable confidence to the application of existing metal standards, but illustrate also how standard values might be widely transportable geographically. © 2012 Elsevier Ltd. All rights reserved.

Utamura M.,Tokyo Institute of Technology
Journal of Engineering for Gas Turbines and Power | Year: 2010

Cycle characteristics of closed gas turbines using supercritical carbon dioxide as a working fluid are investigated. It is found that an anomalous behavior of the physical properties of CO2 at the pseudocritical point may limit the heat exchange rate of a regenerative heat exchanger due to the presence of a pinch point inside the regenerative heat exchanger. Taking such a pinch problem into consideration, the cycle efficiency of the Brayton cycle is assessed. Its value is found to be limited to 39% degraded by 8% compared with the case without the pinch present inside. As an alternative, a part-flow cycle is investigated and its operable range has been identified. It is revealed that the part-flow cycle is effective to recover heat transfer capability and may achieve the cycle thermal efficiency of 45% under maximum operating conditions of 20 MPa and 800 K. Optimal combination of turbine expansion ratio and a part-flow ratio is 2.5 and 0.68, respectively. Parametric study is carried out. In neither compressor nor turbine, deteriorated adiabatic efficiency may affect cycle efficiency significantly. However, pressure drop characteristics of heat exchangers govern the cycle efficiency. © 2010 American Society of Mechanical Engineers.

Hara M.,Tokyo Institute of Technology | Hara M.,Kanagawa Academy Of Science And Technology
Energy and Environmental Science | Year: 2010

Amorphous carbon bearing sulfonic acid groups, a new type of solid Brønsted acid catalyst, was investigated for potential application to environmentally benign biodiesel production and cellulose saccharification. The carbon material exhibits much higher catalytic performance for the esterification of higher fatty acids, transesterification of triglycerides and the hydrolysis of cellulose than conventional solid acid catalysts. © 2010 The Royal Society of Chemistry.

Kawahara Y.,Osaka University | Sugiyama M.,Tokyo Institute of Technology
Statistical Analysis and Data Mining | Year: 2012

Change-point detection is the problem of discovering time points at which properties of time-series data change. This covers a broad range of real-world problems and has been actively discussed in the community of statistics and data mining. In this paper, we present a novel nonparametric approach to detecting the change of probability distributions of sequence data. Our key idea is to estimate the ratio of probability densities, not the probability densities themselves. This formulation allows us to avoid nonparametric density estimation, which is known to be a difficult problem. We provide a change-point detection algorithm based on direct density-ratio estimation that can be computed very efficiently in an online manner. The usefulness of the proposed method is demonstrated through experiments using artificial and real-world datasets. © 2011 Wiley Periodicals, Inc.

Tasaki Y.,Japan National Institute of Advanced Industrial Science and Technology | Okada T.,Tokyo Institute of Technology
Journal of the American Chemical Society | Year: 2012

Ice chromatography measurements have revealed anomalous enhancements of crown ether complexation in a liquid phase coexistent with ice. The 4 orders of magnitude enhancement was confirmed for the complexation of dibenzo-24-crown-8 in sub-μm-sized liquid inclusions formed in ice doped with <1 mM NaCl or KCl. This enhancement became less pronounced with increasing dopant concentration. © 2012 American Chemical Society.

Emelyanenko A.V.,Moscow State University | Ishikawa K.,Tokyo Institute of Technology
Soft Matter | Year: 2013

The possibility of smooth transitions between biaxial smectic subphases via defect propagation is considered on the basis of our theoretical approach reported previously [Emelyanenko et al., Phys. Rev. E, 2006, 74, 011705]. The extrapolation of our results suggests an infinite number of biaxial intermediate phases, each one existing stably only at a particular temperature, and not over a range. Three- and four-layer subphases are confirmed to be important due to the minor differences between them and their neighboring subphases. Some other subphases (including a six-layer subphase) are also found to be very similar to the neighboring subphases. Several sets of intermediate phases are recognized. Each set represents a combination of two typical fragments of the smectic structure in various proportions. © 2013 The Royal Society of Chemistry.

Terashima Y.,Tokyo Institute of Technology | Yamazaki M.,Princeton University
Physical Review Letters | Year: 2012

We show that the smooth geometry of a hyperbolic 3-manifold emerges from a classical spin system defined on a 2D discrete lattice, and moreover, show that the process of this "dimensional oxidation" is equivalent with the dimensional reduction of a supersymmetric gauge theory from 4D to 3D. More concretely, we propose an equality between (1) the 4D superconformal index of a 4D N=1 superconformal quiver gauge theory described by a bipartite graph on T2 and (2) the partition function of a classical integrable spin chain on T2. The 2D spin system is lifted to a hyperbolic 3-manifold after the dimensional reduction and using the Higgs mechanism in the 4D gauge theory. © 2012 American Physical Society.

A new numerical method of analyzing adhesive contact mechanics between a sphere and a flat with sub-nanometer roughness is presented. In contrast to conventional theories, the elastic deformations of mean height surfaces and contacting asperities, and Lennard-Jones (LJ) surface forces of both the contacting asperities and noncontacting rough surfaces including valley areas are taken into account. Calculated contact characteristics of a 2-mm-radius glass slider contacting a magnetic disk with a relatively rough surface and a 30-mm-radius head slider contacting a currently available magnetic disk with lower roughness are shown in comparison with conventional adhesive contact theories. The present theory was found to give a larger adhesive force than the conventional theories and to converge to a smooth sphere-flat contact theory as the roughness height approaches zero. Copyright © 2012 American Society of Mechanical Engineers.

Ormel C.W.,University of California at Berkeley | Ida S.,Tokyo Institute of Technology | Tanaka H.,Hokkaido University
Astrophysical Journal | Year: 2012

Planets migrate due to the recoil they experience from scattering solid (planetesimal) bodies. To first order, the torques exerted by the interior and exterior disks will cancel, analogous to the cancellation of the torques from the gravitational interaction with the gas (Type-I migration). Assuming the dispersion-dominated regime and power laws characterized by indices α and β for the surface density and eccentricity profiles, we calculate the net torque on the planet. We consider both distant encounters and close (orbit-crossing) encounters. We find that the close and distant encounter torques have opposite signs with respect to α and β; and that the torque is especially sensitive to the eccentricity gradient β. Compared to Type-I migration due to excitation of density waves, the planetesimal-driven migration rate is generally lower due to the lower surface density of solids in gas-rich disk, although this may be partially or fully offset when their eccentricity and inclinaton are small. Allowing for the feedback of the planet on the planetesimal disk through viscous stirring, we find that under certain conditions a self-regulated migration scenario emerges, in which the planet migrates at a steady pace that approaches the rate corresponding to the one-sided torque. If the ratio of the local disk mass in planetesimals to planet mass is low, however, migration will stall. We quantify the boundaries separating the three accretion regimes. © 2012. The American Astronomical Society. All rights reserved.

Ormel C.W.,University of California at Berkeley | Okuzumi S.,Tokyo Institute of Technology | Okuzumi S.,Nagoya University
Astrophysical Journal | Year: 2013

A critical phase in the standard model for planet formation is the runaway growth (RG) phase. During RG bodies in the 0.1-100 km size range (planetesimals) quickly produce a number of much larger seeds. The RG phase is essential for planet formation as the emergent planetary embryos can accrete the leftover planetesimals at large gravitational focusing factors. However, torques resulting from turbulence-induced density fluctuations may violate the criterion for the onset of RG, which is that the magnitude of the planetesimals' random (eccentric) motions is less than their escape velocity. This condition represents a more stringent constraint than the condition that planetesimals survive their mutual collisions. To investigate the effects of magneto-rotational instability turbulence on the viability of the RG scenario, we apply our semi-analytical recipes of Paper I, which we augment by a coagulation/fragmentation model for the dust component. We find that the surface-area-equivalent abundance of 0.1 μm particles is reduced by factors 102-103, which tends to render the dust irrelevant to the turbulence. We express the turbulent activity in the midplane regions in terms of a size srun above which planetesimals will experience RG. We find that srun is mainly determined by the strength of the vertical net field that threads the disks and the disk radius. At disk radii beyond 5 AU, srun becomes larger than ∼100 km and the collision times among these bodies longer than the duration of the nebula phase. Our findings imply that the classical, planetesimal-dominated model for planet formation is not viable in the outer regions of a turbulent disk. © 2013. The American Astronomical Society. All rights reserved.

Asano K.,Tokyo Institute of Technology | Meszaros P.,Pennsylvania State University
Astrophysical Journal | Year: 2012

The temporal-spectral evolution of the prompt emission of gamma-ray bursts is simulated numerically for both leptonic and hadronic models. For weak enough magnetic fields, leptonic models can reproduce the few seconds delay of the onset of GeV photon emission observed by Fermi-LAT, due to the slow growth of the target photon field for inverse Compton scattering. For stronger magnetic fields, the GeV delay can be explained with hadronic models, due to the long acceleration timescale of protons and the continuous photopion production after the end of the particle injection. While the FWHMs of the MeV and GeV light curves are almost the same in one-zone leptonic models, the FWHMs of the 1-30 GeV light curves in hadronic models are significantly wider than those of the 0.1-1 MeV light curves. The amount of the GeV delay depends on the importance of the Klein-Nishina effect in both the leptonic and hadronic models. In our examples of hadronic models the energies of the escaped neutrons are comparable to the gamma-ray energy, although their contribution to the ultra high-energy cosmic rays is still subdominant. The resulting neutrino spectra are hard enough to avoid the flux limit constraint from IceCube. The delay of the neutrino emission onset is up to several times longer than the corresponding delay of the GeV photon emission onset. The quantitative differences in the light curves for various models may be further tested with future atmospheric Cerenkov telescopes whose effective area is larger than that of Fermi-LAT, such as CTA. © © 2012. The American Astronomical Society. All rights reserved.

Hasegawa Y.,Academia Sinica, Taiwan | Ida S.,Tokyo Institute of Technology
Astrophysical Journal | Year: 2013

Planetary migration is one of the most serious problems to systematically understand the observations of exoplanets. We clarify that the theoretically predicted type II, migration (like type I migration) is too fast, by developing detailed analytical arguments in which the timescale of type II migration is compared with the disk lifetime. In the disk-dominated regime, the type II migration timescale is characterized by a local viscous diffusion timescale, while the disk lifetime is characterized by a global diffusion timescale that is much longer than the local one. Even in the planet-dominated regime where the inertia of the planet mass reduces the migration speed, the timescale is still shorter than the disk lifetime except in the final disk evolution stage where the total disk mass decays below the planet mass. This suggests that most giant planets plunge into the central stars within the disk lifetime, and it contradicts the exoplanet observations that gas giants are piled up at r ≳ 1 AU. We examine additional processes that may arise in protoplanetary disks: dead zones, photoevaporation of gas, and gas flow across a gap formed by a type II migrator. Although they make the type II migration timescale closer to the disk lifetime, we show that none of them can act as an effective barrier for rapid type II migration with the current knowledge of these processes. We point out that gas flow across a gap and the fraction of the flow accreted onto the planets are uncertain and they may have the potential to solve the problem. Much more detailed investigation for each process may be needed to explain the observed distribution of gas giants in extrasolar planetary systems. © 2013. The American Astronomical Society. All rights reserved.

Aziz M.,Tokyo Institute of Technology
Energy Conversion and Management | Year: 2015

Integrated energy utilization processes for microalgae based on enhanced process integration are proposed in this study. They consist of supercritical water gasification and combined cycle for power generation. The enhanced process integration is developed based on exergy recovery and process integration technologies. Exergy recovery deals with effective heat circulation throughout a single process which is achieved by exergy elevation and efficient heat coupling. In addition, process integration utilizes the unrecoverable heat from a single process for other processes, thus minimizing the total exergy destruction of the whole integrated processes. Microalga Spirulina sp. is selected as the sample due to its higher gasification and carbon conversion efficiencies than any other microalgae. Process simulation is performed to evaluate the total energy efficiency, specifically the effect of steam flow rate (fluidization velocity), gasification pressure and turbine inlet temperature. Simulation reveals that the proposed integrated processes harvest the energy from microalgae with total energy efficiency exceeding 40%. A temperature-enthalpy diagram shows that the heat involved in the whole processes is recovered effectively. © 2014 Elsevier Ltd. All rights reserved.

Akita M.,Tokyo Institute of Technology
Organometallics | Year: 2011

Recent progress of photochromic metal complexes is summarized with emphasis on "photochromic organometallics" with a M-C(photochromic unit) bond. Stimuli-responsive systems including the photochromic system are essential components of smart chemical systems, where the system recognizes changes of the environment so as to trigger a chemical function required for the smart chemical system. Combination with metal components, which exhibit unique properties such as redox and photophysical properties and catalysis, should lead to more sophisticated systems. Photophysical properties (e.g., luminescence) have been the major research subject of photochromic coordination compounds, whereas for "photochromic organometallics", a limited number of studies on switching of catalytic activity of metal-catalyzed organic transformation and application to molecular devices have been reported. Intriguing switching systems (e.g., performance of organometallic molecular wire and multimodal stimuli-responsive system) have been realized by the use of dithienylethene, a representative photochromic molecule. Future prospects of "photochromic organometallics" are discussed in the final part. © 2011 American Chemical Society.

Ikariya T.,Tokyo Institute of Technology
Bulletin of the Chemical Society of Japan | Year: 2011

The development of conceptually new bifunctional transition-metal-based catalysts for a wide range of catalytic reactions is described. The bifunctional chiral molecular catalyst based on metalligand cooperation was originally developed for asymmetric transfer hydrogenation of ketones and imines and is now applicable to chemo- and stereoselective reductive and oxidative transformations as well as to enantioselective CC and CN bond formations with a wide scope and high practicability. The structural modification and electronic fine-tuning of the protic amine chelating ligands are crucial to develop unprecedented catalytic reactions. Cp*Ru complexes bearing a diamine (NN) or aminophosphine (PN) ligand readily activate H2, and can effect hydrogenation of polar functionalities. The bifunctional Ir complexes promote aerobic oxidative transformation of alcohols into ketones and esters and are applicable to kinetic resolution of racemic secondary alcohols. A novel imido-bridged dirhodium complex, which is a dinuclear variant of the bifunctional mononuclear amido complexes, promotes aerobic oxidation of a secondary alcohol and H2. In addition, the metal/NH bifunctional property also affects efficiently enantioselective conjugate additions. The present concerto molecular catalysts offer a great opportunity to open up new fundamentals for stereoselective molecular transformations. © 2011 The Chemical Society of Japan.

Chakraborty T.,Indian Association for The Cultivation of Science | Ray S.,Indian Association for The Cultivation of Science | Itoh M.,Tokyo Institute of Technology
Physical Review B - Condensed Matter and Materials Physics | Year: 2011

Single crystalline Fe-doped hexagonal BaTiO3 samples with varying oxygen content are created by specifically intended post-growth annealing treatments, in order to check the influence of defects on the unusual high temperature ferromagnetism observed in this system. The various defects have been shown to play a crucial role in dilute magnetic systems and therefore, it is important to carry out this check for the Fe-doped BaTiO3 system also, in which unusual ferromagnetism was reported even in its bulk single crystalline form. The x-ray diffraction and dielectric studies carried out here have confirmed that the Fe doping of Ti is intrinsic, while the high resolution transmission electron microscopy (HRTEM) and x-ray photoemission spectroscopy (XPS) studies proved the absence of unwanted magnetic metal clusters in the sample. The transport studies show that the oxygen concentrations could be varied substantially by the thermal treatments. Finally, magnetization measurements on the samples demonstrated that ferromagnetism is stronger in samples with higher oxygen deficiency, which could interestingly be retreated under high oxygen atmosphere and reversibly be taken back to a lower magnetic state. The vacancy-induced ferromagnetism is further confirmed by EPR measurements, which is consistent with earlier studies and, consequently, put the doped BaTiO3 in the list of true dilute magnetic oxide (DMO) systems. © 2011 American Physical Society.

Watanabe S.,Tokyo Institute of Technology
Neural Networks | Year: 2010

Learning machines that have hierarchical structures or hidden variables are singular statistical models because they are nonidentifiable and their Fisher information matrices are singular. In singular statistical models, neither does the Bayes a posteriori distribution converge to the normal distribution nor does the maximum likelihood estimator satisfy asymptotic normality. This is the main reason that it has been difficult to predict their generalization performance from trained states. In this paper, we study four errors, (1) the Bayes generalization error, (2) the Bayes training error, (3) the Gibbs generalization error, and (4) the Gibbs training error, and prove that there are universal mathematical relations among these errors. The formulas proved in this paper are equations of states in statistical estimation because they hold for any true distribution, any parametric model, and any a priori distribution. Also we show that the Bayes and Gibbs generalization errors can be estimated by Bayes and Gibbs training errors, and we propose widely applicable information criteria that can be applied to both regular and singular statistical models. © 2009 Elsevier Ltd. All rights reserved.

Kawano Y.,Tokyo Institute of Technology
Laser and Photonics Reviews | Year: 2012

The advantageous properties of terahertz (THz) waves, such as permeability through objects that are opaque for visible light and the energy spectrum in the microelectron-volt range that are important in materials research, allow their potential use in various applications of sensing and imaging. However, since the THz region is located between the electronic and photonic bands, even the basic components such as detectors and sources have not been fully developed, unlike in other frequency regions. THz technology also has the problem of low imaging resolution, which results from a considerably longer wavelength than that of the visible light. However, the utilization of nanostructured electronic devices has recently opened up new horizons for THz sensing and imaging. This paper provides an overview of the THz detector and imaging techniques and tracks their recent progress. Specifically, two cutting-edge techniques, namely, frequency-selective THz-photon detection and integrated near-field THz imaging, are discussed in detail. Finally, the studies of superconductors and semiconductors with high-resolution THz imaging are described. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Chiba T.,Nihon University | Yamaguchi M.,Tokyo Institute of Technology
Journal of Cosmology and Astroparticle Physics | Year: 2013

We provide the correspondence between the variables in the Jordan frame and those in the Einstein frame in scalar-tensor gravity and consider the frame-(in)dependence of the cosmological observables. In particular, we show that the cosmological observables/relations (redshift, luminosity distance, temperature anisotropies) are frame-independent. We also study the frame-dependence of curvature perturbations and find that the curvature perturbations are conformal invariant if the perturbation is adiabatic and the entropy perturbation between matter and the Brans-Dicke scalar is vanishing. The relation among various definitions of curvature perturbations in the both frames is also discussed, and the condition for the equivalence is clarified. © 2013 IOP Publishing Ltd and Sissa Medialab srl.

Prediction of the thermodynamic behaviors of biomolecules at high temperature and pressure is fundamental to understanding the role of hydrothermal systems in the origin and evolution of life on the primitive Earth. However, available thermodynamic dataset for amino acids, essential components for life, cannot represent experimentally observed polymerization behaviors of amino acids accurately under hydrothermal conditions. This report presents the thermodynamic data and the revised HKF parameters for the simplest amino acid "Gly" and its polymers (GlyGly, GlyGlyGly and DKP) based on experimental thermodynamic data from the literature. Values for the ionization states of Gly (Gly+ and Gly-) and Gly peptides (GlyGly+, GlyGly-, GlyGlyGly+, and GlyGlyGly-) were also retrieved from reported experimental data by combining group additivity algorithms. The obtained dataset enables prediction of the polymerization behavior of Gly as a function of temperature and pH, consistent with experimentally obtained results in the literature. The revised thermodynamic data for zwitterionic Gly, GlyGly, and DKP were also used to estimate the energetics of amino acid polymerization into proteins. Results show that the Gibbs energy necessary to synthesize a mole of peptide bond is more than 10 kJ mol-1 less than previously estimated over widely various temperatures (e.g., 28.3 kJ mol-1 → 17.1 kJ mol-1 at 25 °C and 1 bar). Protein synthesis under abiotic conditions might therefore be more feasible than earlier studies have shown. © 2014 Springer Science+Business Media New York.

Ikoma M.,University of Tokyo | Ikoma M.,Tokyo Institute of Technology | Hori Y.,Japan National Astronomical Observatory
Astrophysical Journal | Year: 2012

Motivated by recent discoveries of low-density super-Earths with short orbital periods, we have investigated in situ accretion of H-He atmospheres on rocky bodies embedded in dissipating warm disks, by simulating quasi-static evolution of atmospheres that connect to the ambient disk. We have found that the atmospheric evolution has two distinctly different outcomes, depending on the rocky body's mass: while the atmospheres on massive rocky bodies undergo runaway disk-gas accretion, those on light rocky bodies undergo significant erosion during disk dispersal. In the atmospheric erosion, the heat content of the rocky body that was previously neglected plays an important role. We have also realized that the atmospheric mass is rather sensitive to disk temperature in the mass range of interest in this study. Our theory is applied to recently detected super-Earths orbiting Kepler-11 to examine the possibility that the planets are rock-dominated ones with relatively thick H-He atmospheres. The application suggests that the in situ formation of the relatively thick H-He atmospheres inferred by structure modeling is possible only under restricted conditions, namely, relatively slow disk dissipation and/or cool environments. This study demonstrates that low-density super-Earths provide important clues to understanding of planetary accretion and disk evolution. © 2012. The American Astronomical Society. All rights reserved.

Kanamori T.,Nagoya University | Suzuki T.,University of Tokyo | Sugiyama M.,Tokyo Institute of Technology
Machine Learning | Year: 2012

The ratio of two probability densities can be used for solving various machine learning tasks such as covariate shift adaptation (importance sampling), outlier detection (likelihood-ratio test), feature selection (mutual information), and conditional probability estimation. Several methods of directly estimating the density ratio have recently been developed, e.g., moment matching estimation, maximum-likelihood density-ratio estimation, and least-squares density-ratio fitting. In this paper, we propose a kernelized variant of the least-squares method for density-ratio estimation, which is called kernel unconstrained leastsquares importance fitting (KuLSIF). We investigate its fundamental statistical properties including a non-parametric convergence rate, an analytic-form solution, and a leave-oneout cross-validation score. We further study its relation to other kernel-based density-ratio estimators. In experiments, we numerically compare various kernel-based density-ratio estimation methods, and show that KuLSIF compares favorably with other approaches. © The Author(s) 2011.

Takeuchi D.,Tokyo Institute of Technology
Macromolecular Chemistry and Physics | Year: 2011

Pd complexes with diimine ligands promote polymerization of cyclopentenes, 1,6-dienes, and 1,6,11-trienes to afford polymers having 1,2- or 1,3-five-membered ring in every repeating unit. The Pd complexes with C 2 symmetrical structure catalyze the polymerization reactions to produce polymers with high stereoselectivity. Some of the obtained polymers show characteristic properties such as thermoreversible gelation and liquid crystal formation. Ni complexes bring about the cyclopolymerization of the dienes to afford polymers containing five- and/or six-membered rings in controlled stereochemistry. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Yamanaka A.,Tokyo Institute of Technology
Nihon Kikai Gakkai Ronbunshu, C Hen/Transactions of the Japan Society of Mechanical Engineers, Part C | Year: 2011

A new fabrication method of ordered metal nano dot array is developed by using coating, nano plastic forming (NPF) and self-assembly due to annealing. In this study, the combination of these processes is studied to produce uniformly-sized and ordered gold nano dot array on a quarts glass substrate experimentally. The results reveal that patterning of lattice grooves on the gold-coated substrate with the NPF is effective to obtain the ordered gold nano dot array. In the proposed fabrication process, the size of the gold nano dot can be controlled by adjusting pitch of the groove. Furthermore, to investigate the effect of the NPF on the dot ordering, the multi-phase-field simulation of the self-assembly of the gold thin-film during the annealing is performed. From the simulation results, it is revealed that the grooves formed by the NPF become a starting point for the dot-formation during the annealing and the surface patterning by the NPF plays an important role for the fabrication of the ordered nano dot array. © 2011 The Japan Society of Mechanical Engineers.

Helffrich G.,Tokyo Institute of Technology
Earth, Planets and Space | Year: 2015

The hard sphere model for liquids attempts to capture the physical behavior of a real liquid in a simple conceptual model: a fluid of fixed size spheres that only interact repulsively when they come into contact. Is the model good enough to use for modeling internal planetary structure? To answer this question, I survey variants of hard sphere liquid theory by applying them to the Earth's outer core to determine which of them explains wavespeeds in the outer core best. The variants explored here are the Carnahan-Starling hard sphere model, the Mansoori-Canfield extension to hard sphere mixtures, the transition metal hard sphere liquid, and the Lennard-Jones hard sphere liquid with attractive forces. With an empirical addition of a temperature dependence to the liquid's hard sphere diameter, all of the variants explored can replicate wavespeeds in most of the radius range of the outer core. The hard sphere model for liquid transition metals explains the wavespeed best because it yields a mean liquid atomic weight of 48.8 g mol -1 at 10 wt% light element abundance in the core which is in good cosmochemical agreement with core light element models. Other variants also fit core wavespeeds but require implausibly low liquid mean atomic weight implying excessive incorporation of hydrogen or helium in the core. Applied to the detailed wavespeed structure of the Earth's outermost outer core, the model suggests that the mean atomic weight could be reduced by up to 1.74% or the temperature could be increased by up to 400 K relative to an adiabatic profile, or there could be 8% fewer valence electrons in the liquid. © 2015 Helffrich; licensee Springer.

Wakahara T.,Hosei University | Yamashita Y.,Tokyo Institute of Technology
Pattern Recognition | Year: 2014

This paper addresses the problem of reinforcing the ability of the k-NN classification of handwritten characters via distortion-tolerant template matching techniques with a limited quantity of data. We compare three kinds of matching techniques: the conventional simple correlation, the tangent distance, and the global affine transformation (GAT) correlation. Although the k-NN classification method is straightforward and powerful, it consumes a lot of time. Therefore, to reduce the computational cost of matching in k-NN classification, we propose accelerating the GAT correlation method by reformulating its computational model and adopting efficient lookup tables. Recognition experiments performed on the IPTP CDROM1B handwritten numerical database show that the matching techniques of the simple correlation, the tangent distance, and the accelerated GAT correlation achieved recognition rates of 97.07%, 97.50%, and 98.70%, respectively. The computation time ratios of the tangent distance and the accelerated GAT correlation to the simple correlation are 26.3 and 36.5 to 1.0, respectively. © 2013 Elsevier Ltd. All rights reserved.

Siino M.,Tokyo Institute of Technology
International Journal of Modern Physics D | Year: 2013

We evaluate the amount of energy that can be converted into gravitational radiation in head-on collision of black holes. We estimate it by the area theorem of black hole horizon incorporating merging entropy of colliding black holes from a viewpoint of black hole thermodynamics. Then we obtain an upper bound of energy ratio of the gravitational radiation which is smaller than the upper bound originally derived by Hawking. The fact that this estimation is not inconsistent with the results of both numerical investigations in low- and high-energy head-on collision implies that thermodynamics of coalescing black holes requires the contribution of the merging entropy. © 2013 World Scientific Publishing Company.

Murakami T.,Tokyo Institute of Technology
Energy Conversion and Management | Year: 2014

Agent-based simulations coupled with an analysis of the flow of electric power are carried out to examine the influence of the social policy of the government and the neighboring communication between customers on the adoption of distributed rooftop photovoltaic electrical power generators (PVs). How the relationships between the social policy and the possibility of a reverse current restriction give rise to the collective behavior of autonomous individuals, and how the end customers interact and form relationships with its environment are described. Strong intervention by the government in the areas near a main high-voltage power distribution transformer, where the possibility of a reverse current restriction is relatively low, drives the greatest adoption of the PV system. The near areas are primarily occupied by customers with only a PV to improve the diffusion rate of PVs via the self-organization by the communication between customers. It also lead in a decrease in the need for compensation devices, which in turn minimizes the social cost. Growth in the number of PVs in areas far from the transformer is assisted by the installation of batteries as compensation for the lost opportunity due to restrictions in those areas on reverse power currents. Therefore, excessive intervention by the government in the far areas results in an increase in the social cost of managing reverse currents. © 2014 Elsevier B.V.

Mazumdar A.,Lancaster University | Noumi T.,RIKEN | Yamaguchi M.,Tokyo Institute of Technology
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2014

Shift symmetry is essential to protect the flatness of the potential, even beyond the super-Planckian vacuum expectation value for an inflaton field. The breaking of the shift symmetry can yield potentials suitable for super-Planckian excursion of the inflaton. The aim of this paper is to illustrate that it is indeed possible to break the shift symmetry dynamically within four-dimensional supergravity prior to a long phase of inflation. Thanks to the shift symmetry, the leading contribution to the inflaton potential is free from the dangerous exponential factor even after its breaking, which is the main obstacle to realizing the super-Planckian inflation in supergravity. But, in our simple model, the resulting inflaton potential is a cosine-type potential rather than the power-law one, and it is difficult to realize a super-Planckian breaking scale, unfortunately. © 2014 American Physical Society.

Gubler P.,RIKEN | Ohtani K.,Tokyo Institute of Technology
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2014

The behavior of the φ meson at finite density is studied, making use of a QCD sum rule approach in combination with the maximum entropy method. It is demonstrated that a possible mass shift of the φ in nuclear matter is strongly correlated to the strangeness content of the nucleon, which is proportional to the strange sigma term, σsN=msas¯s|N. Our results furthermore show that, depending on the value of σsN, the φ meson could receive both a positive or negative mass shift at nuclear matter density. We find that these results depend only weakly on potential modifications of the width of the φ peak and on assumptions made on the behavior of four-quark condensates at finite density. To check the stability of our findings, we take into account several higher order corrections to the operator product expansion, including αs-corrections, terms of higher order in the strange quark mass, and terms of higher twist that have not been considered in earlier works. © 2014 American Physical Society.

Takahashi K.,Tokyo Institute of Technology | Ohzeki M.,Kyoto University
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2016

We consider the optimization of Markovian dynamics to pursue the fastest convergence to the stationary state. The brachistochrone method is applied to the continuous-time master equation for finite-size systems. The principle of least action leads to a brachistochrone equation for the transition-rate matrix. Three-state systems are explicitly analyzed, and we find that the solution violates the detailed balance condition. The properties of the solution are studied in detail to observe the optimality of the solution. We also discuss the counterdiabatic driving for the Markovian dynamics. The transition-rate matrix is then divided into two parts, and the state is given by an eigenstate of the first part. The second part violates the detailed balance condition and plays the role of a counterdiabatic term. © 2016 American Physical Society.

Gao X.,Tokyo Institute of Technology
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2014

We perform the Hamiltonian constraint analysis for a wide class of gravity theories that are invariant under spatial diffeomorphism. With a very general setup, we show that different from the general relativity, the primary and secondary constraints associated with the lapse function N become second class, as long as the lapse function N enters the Hamiltonian nonlinearly. This fact implies that there are 3 degrees of freedom are propagating, of which two correspond to the usual tensor-type transverse and traceless gravitons, and one is the scalar-type graviton. By restoring the full spacetime diffeomorphism using the Stückelberg trick, this type of spatially covariant gravity theory corresponds to a large class of single field scalar-tensor theories that possess higher order derivatives in the equations of motion, and thus is beyond the scope of the Horndeski theory. © 2014 American Physical Society.

Rossman B.,Tokyo Institute of Technology
SIAM Journal on Computing | Year: 2014

We present lower and upper bounds showing that the average-case complexity of the k-Clique problem on monotone circuits is nk/4+O(1). Similar bounds for AC0 circuits were shown in Rossman [Proceedings of the 40th Annual ACM Symposium on Theory of Computing, 2008, pp. 721-730] and Amano [Comput. Complexity, 19 (2010), pp. 183-210]. © by SIAM.

Kanamori T.,Nagoya University | Suzuki T.,University of Tokyo | Sugiyama M.,Tokyo Institute of Technology
IEEE Transactions on Information Theory | Year: 2012

A density ratio is defined by the ratio of two probability densities. We study the inference problem of density ratios and apply a semiparametric density-ratio estimator to the two-sample homogeneity test. In the proposed test procedure, the f-divergence between two probability densities is estimated using a density-ratio estimator. The f-divergence estimator is then exploited for the two-sample homogeneity test. We derive an optimal estimator of f-divergence in the sense of the asymptotic variance in a semiparametric setting, and provide a statistic for two-sample homogeneity test based on the optimal estimator. We prove that the proposed test dominates the existing empirical likelihood score test. Through numerical studies, we illustrate the adequacy of the asymptotic theory for finite-sample inference. © 2011 IEEE.

Morgan T.A.,Tokyo Institute of Technology | Mahin S.A.,University of California at Berkeley
Earthquake Engineering and Structural Dynamics | Year: 2010

An objective in the design of seismically isolated structures is the selection of isolator properties so that performance enhancements are reliably achieved over a range of excitations and performance metrics. A challenge in the design of isolation systems is that, to withstand very severe or near-fault motions, bearings often become so large, stiff and strong that they provide little isolation during moderate seismic events. Numerical investigations are presented to characterize the performance of a new multi-stage friction pendulum (FP) isolation bearing, capable of progressively exhibiting different hysteretic properties at various levels of displacement demand. The feasibility of targeting these properties to achieve specific performance goals for a range of ground motion intensities and structural dynamic characteristics is investigated. In particular, the trade-off between limiting very rare isolator displacement demands and inducing high inter-story drift and floor accelerations is examined for a range of levels of seismic hazard. Nonlinear dynamic analyses of realistic building systems are presented, including a description of key structural demand parameters. To investigate the potential performance benefits of innovative devices, a complex multi-level performance objective termed a seismic performance classification is introduced. Results indicate that multi-stage FP bearings show improved reliability of meeting seismic performance objectives when multiple levels of seismic intensity are considered compared to those systems that incorporate conventional bilinear hysteretic energy dissipation mechanisms. © 2010 John Wiley & Sons, Ltd.

You J.H.,California Institute of Technology | Inaba K.,Tokyo Institute of Technology
Journal of Fluids and Structures | Year: 2013

The effects of elastic anisotropy in piping materials on fluid-structure interaction are studied for water-filled carbon-fiber reinforced thin plastic pipes. When an impact is introduced to water in a pipe, there are two waves traveling at different speeds. A primary wave corresponding to a breathing mode of pipe travels slowly and a precursor wave corresponding to a longitudinal mode of pipe travels fast. An anisotropic stress-strain relationship of piping materials has been taken into account to describe the propagation of primary and precursor waves in the carbon-fiber reinforced thin plastic pipes. The wave speeds and strains in the axial and hoop directions are calculated as a function of carbon-fiber winding angles and compared with the experimental data. As the winding angle increases, the primary wave speed increases due to the increased stiffness in the hoop direction, while the precursor wave speed decreases. The magnitudes of precursor waves are much smaller than those of primary waves so that the effect of precursor waves on the deformation of pipe is not significant. The primary wave generates the hoop strain accompanying the opposite-signed axial strain through the coupling compliance of pipe. The magnitude of hoop strain induced by the primary waves decreases with increasing the winding angle due to the increased hoop stiffness of pipe. The magnitude of axial strain is small at low and high winding angles where the coupling compliance is small. © 2012 Elsevier Ltd.

This paper deals with a resonant gate-drive circuit for fast-switching and high-voltage power semiconductor devices, which is equipped with optical fibers for both gate control signal and dc power supply. A resonant inductor connected with the gate terminal makes it possible to charge or discharge the gate-to-source voltage by using the parallel resonance between the inductor and the input capacitance of the device. The optical fibers can be used to deliver the driving power to the gate-drive circuit, because the circuit theoretically causes no power consumption for driving the power device. Moreover, the proposed circuit makes it possible to suppress fluctuations in the gate voltage caused by a rapid change in the drain-to-source voltage. Experimental results are shown to verify the viability of the proposed circuit. © 1986-2012 IEEE.

Ceria-based materials are utilized as automotive exhaust catalysts for the removal of noxious compounds, as catalysts for reforming ethanol and methane to produce hydrogen in fuel cells, as materials for solar-energy-to-fuel conversion, and as cathode, anode, and electrolyte materials in solid oxide fuel cells (SOFCs). The present paper is a critical review on the atomic-scale characterization of oxide-ion diffusion pathway, the existing phases, the phase transformations, "metastable" and stable phase diagrams, and oxygen storage capacity (OSC) of ceria-based materials. "Metastable," compositionally (x) homogeneous t′- and t″-ceria-zirconia CexZr1-xO2 solid solutions (0.2 < x < 0.9) are key materials to obtain a high OSC, leading to high catalytic activity. Here, the t′- and t″-forms are unstable compared to the two-phase mixture of stable ZrO2-rich tetragonal and CeO2-rich cubic (or t″) phases, but are stable in the partitionless, compositionally homogeneous phases. The axial ratio, c/aF where the subscript F represents the pseudo-fluorite lattice, of the t′-form is larger than unity, while the c/aF ratio of the t″-form equals unity. Formation of the t′- and t″-CexZr1-xO2 is depicted in the "metastable" phase diagram consisting of allotropic phase boundaries in the CeO2-ZrO2 system and is explained using the schematic Gibbs energy-composition (G-x) diagram. The composition (CeO2 content x)-induced t′-t″ transition in CexZr1-xO2 is discrete and of first order. The c-t″ phase transition of CexZr1-xO2 is induced by the oxygen displacement from the regular fluorite position 1/4,1/4,1/4 along the c-axis. The c-t″ transition is continuous and might be of higher order. The c-t″ phase boundary at room temperature is located at around x = 0.85-0.9 in both bulk and nanocrystalline CexZr1-xO2. The tetragonal symmetry of compositionally homogeneous nano-sized Ce0.5Zr0.5O2 in air is retained up to 1176 K. The c/aF ratio, and the oxygen displacement are smaller in the nanocrystalline Ce0.5Zr0.5O2 than in bulk Ce0.5Zr0.5O2. Bulk oxide-ion diffusion is an important step of oxygen storage and release in ceria-based catalysts, and the oxide-ion diffusivity is essential for high OSC and efficiency of the SOFCs and the solar-energy-to-fuel conversion. The present paper reviews the atomic-scale characterization of ion diffusion in ceria-based catalysts and fluorite-type ionic conductors and discusses the correlation between their bulk ion diffusivity and structural properties. The spatial distributions of neutron scattering length density, bond valence sum (BVS), and bond-valence-based energy (BVE) in the unit cell of tetragonal ceria-zirconia compounds, cubic fluorite-type ceria-based materials, and other fluorite-structured compounds such as Ce0.5Zr0.5O2, CeO2, ceria-yttria Ce0.97Y0.07O1.96, bismuth oxide solid solution δ-Bi1.4Yb0.6O3, and copper iodide α-CuI indicate the three-dimensional network of curved (1 0 0)F ion diffusion pathways and anisotropic (1 1 1)F thermal vibration of mobile ions, which are responsible for the bulk ion diffusion and conduction. Here, the subscript F denotes the pseudo-fluorite lattice. The BVE distributions of Ce0.5Zr0.5O2 and CeO2 indicate lower activation energy and higher mobility of oxide ions in Ce0.5Zr0.5O2 compared with CeO2. © 2015 Elsevier B.V. All rights reserved.

Dominguez-Rodriguez A.,University of Seville | Gomez-Garcia D.,University of Seville | Wakai F.,Tokyo Institute of Technology
International Materials Reviews | Year: 2013

The literature data on the superplastic deformation of high purity yttria stabilised tetragonal zirconia polycrystals is reviewed in detail. It is shown that, based on the existence of a threshold stress, the single mechanism of grain boundary sliding (GBS) accommodated by diffusional processes can explain the superplasticity of these materials over all the ranges of temperature, stress, grain size, and surrounding atmosphere that have been studied. The origin of the threshold stress and its quantitative dependence on temperature and grain size is explained in terms of the segregation of yttrium atoms at the grain boundaries. A new model for GBS accommodated by lattice or grain-boundary diffusion is presented which can explain the transition of the stress exponent from 2 to 1. © 2013 Institute of Materials, Minerals and Mining and ASM International Published by Maney for the Institute and ASM International.

Maeda K.,Tokyo Institute of Technology | Maeda K.,Japan Science and Technology Agency
ACS Catalysis | Year: 2013

Water splitting on illuminated semiconductors has long been studied as a potential means of converting solar energy into chemical energy in the form of H2, a clean and renewable energy carrier. Photocatalytic water splitting through two-step photoexcitation using two different semiconductor powders and a reversible donor/acceptor pair (so-called shuttle redox mediator) is one of the possible forms of artificial photosynthesis. This system was inspired by natural photosynthesis in green plants and is called the "Z-scheme". The development of Z-scheme water splitting systems has relied on both finding a new semiconductor photocatalyst that efficiently works in the presence of a shuttle redox mediator and creating active sites to promote surface chemical reactions while suppressing backward reactions involving redox mediators. This review article describes the historical development of photocatalytic water splitting systems driven by the Z-scheme principle. © 2013 American Chemical Society.

Kasuya H.,Tokyo Institute of Technology
Journal of Geometry and Physics | Year: 2014

Let G=Cn⋉φCm with a semi-simple action φ:Cn→GLm(C) (not necessarily holomorphic). Suppose that G has a lattice Γ. Then we show that under some conditions on G and Γ, G / Γ admits a Hermitian metric such that the space of harmonic forms satisfies the Hodge symmetry and decomposition. By this result we give many examples of non-Kähler Hermitian solvmanifolds satisfying the Hodge symmetry and decomposition. © 2013 Elsevier B.V.

Gao X.,Tokyo Institute of Technology
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2014

A general framework for effective theories propagating two tensor and one scalar degrees of freedom is investigated. Geometrically, it describes dynamical foliation of spacelike hypersurfaces coupled to a general background, in which the scalar mode encodes the fluctuation of the hypersurfaces. Within this framework, various models in the literature - including k-essence, Horndeski theory, the effective field theory of inflation, ghost condensate as well as the Hořava gravity - get unified. Our framework generalizes the Horndeski theory in the sense that, it propagates the correct number of degrees of freedom, although the equations of motion are generally higher order. We also identify new operators beyond the Horndeski theory, which yield second order equations of motion for linear perturbations around a Friedmann-Robertson-Walker background. © 2014 American Physical Society.

Iga K.,Tokyo Institute of Technology
Proceedings of the IEEE | Year: 2013

The vertical-cavity surface-emitting laser (VCSEL) is becoming a key device in high-speed optical local area networks (LANs) and even wide-area networks (WANs). This device is also enabling ultraparallel data transfer in equipment and computer systems, including storage area networks (SANs) and wide optoelectronics fields. In this paper, we will review its physics and the progress of technology covering the spectral band from infrared to ultraviolet by featuring materials and fabrication technology. Performances such as threshold, output power, polarization, modulation, and reliability are introduced. Last, we will touch on its future prospects. © 1963-2012 IEEE.

Mori R.,Tokyo Institute of Technology
IEEE Transactions on Information Theory | Year: 2015

The Bethe approximation is a well-known approximation of the partition function used in statistical physics. Recently, an equality relating the partition function and its Bethe approximation was obtained for graphical models with binary variables by Chertkov and Chernyak. In this equality, the multiplicative error in the Bethe approximation is represented as a weighted sum over all generalized loops in the graphical model. In this paper, the equality is generalized to graphical models with nonbinary alphabet using concepts from information geometry. © 2015 IEEE.

Matsuda T.,Tokyo Institute of Technology
Journal of Bioscience and Bioengineering | Year: 2013

The latest advances in biocatalysis using supercritical carbon dioxide (scCO2) are reviewed. Stability and stabilization methodologies of enzymes in scCO2 as well as reactions for organic synthesis are described. Especially, varieties of examples for lipase-catalyzed synthesis of chiral compounds using scCO2 are given. Furthermore, asymmetric reduction by alcohol dehydrogenase in scCO2 and carboxylation by decarboxylase in scCO2 are also introduced. © 2012 The Society for Biotechnology, Japan.

Sato S.,Toyota Central Research and Development Laboratories Inc. | Sato S.,Japan Science and Technology Agency | Ishitani O.,Tokyo Institute of Technology
Coordination Chemistry Reviews | Year: 2015

The photochemical ligand substitution and isomerization reactions of fac-[ReI(L-L')(CO)3(L″)]n+-type complexes are reviewed. We especially focus on the mechanistic studies of the these reactions for affording deeper insights into energetically higher excited states of Re(I) complexes, other than the lowest 3MLCT excited state. Moreover, application of the photochemical reactions for synthesis of the linear-shaped and ring-shaped Re(I) multinuclear complexes is described. © 2014 Elsevier B.V.

Hyodo T.,Tokyo Institute of Technology
Nuclear Physics A | Year: 2013

Stimulated by various experimental achievements, the study of K-N dynamics now enters a new phase. The two-body K-N interaction is largely constrained by recent experimental data, and the nature of the Λ(1405) resonance is being unveiled by several theoretical analyses. These findings provide a basic tool for applications to K--nuclear systems. We summarize the current status of the K-N phenomenology and outline the future direction in this field. © 2013 Elsevier B.V.

Osakada K.,Tokyo Institute of Technology
Angewandte Chemie - International Edition | Year: 2011

Making introductions: A half-sandwich Ru complex catalyzes the hydrosilylation of pyridine derivatives to produce N-silyl-3-hydropyridine through a 1,4-addition of the Si-H group (see scheme). The reversibility of the hydrosilylation was suggested based on the experimental results. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Noumi T.,RIKEN | Yamaguchi M.,Tokyo Institute of Technology
Journal of Cosmology and Astroparticle Physics | Year: 2013

Effects of heavy fields on primordial spectra of curvature perturbations are discussed in inflationary models with a sudden turning trajectory. When heavy fields are excited after the sudden turn and oscillate around the bottom of the potential, the following two effects are generically induced: deformation of the inflationary background spacetime and conversion interactions between adiabatic and isocurvature perturbations, both of which can affect the primordial density perturbations. In this paper, we calculate primordial spectra in inflationary models with sudden turning potentials taking into account both of the two effects appropriately. We find that there are some non-trivial correlations between the two effects in the power spectrum and, as a consequence, the primordial scalar power spectrum has a peak around the scale exiting the horizon at the turn. Though both effects can induce parametric resonance amplifications, they are shown to be canceled out for the case with the canonical kinetic terms. The peak feature and the scale dependence of bispectra are also discussed. © 2013 IOP Publishing Ltd and Sissa Medialab srl.

Imamura Y.,Tokyo Institute of Technology
Progress of Theoretical and Experimental Physics | Year: 2013

We construct supersymmetric theories on the SU(3) × U(1) symmetric squashed five-sphere with 2, 4, 6, and 12 supercharges. We first determine the Killing equation by dimensional reduction from 6d, and use the Noether procedure to construct actions. The supersymmetric Yang-Mills action is straightforwardly obtained from the supersymmetric Chern-Simons action by using a supersymmetry-preserving constant vector multiplet. © The Author(s) 2013..

Ambjorn J.,Copenhagen University | Ambjorn J.,Radboud University Nijmegen | Glaser L.,Copenhagen University | Sato Y.,Nagoya University | Watabiki Y.,Tokyo Institute of Technology
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2013

Causal Dynamical Triangulations (CDT) is a lattice theory where aspects of quantum gravity can be studied. Two-dimensional CDT can be solved analytically and the continuum (quantum) Hamiltonian obtained. In this Letter we show that this continuum Hamiltonian is the one obtained by quantizing two-dimensional projectable Hořava-Lifshitz gravity. © 2013.

Frank B.,Tokyo Institute of Technology
Managing Service Quality | Year: 2012

Purpose: Past research showed that overly positive attitudes and intentions towards fast food contribute to obesity. In the face of rising childhood obesity, the purpose of this paper is to explore attitudinal and behavioral reasons behind adolescents' suboptimal food choices. It tests hypotheses about differences between teenagers and adults in customer attitudes and intentions regarding fast food restaurants. Design/methodology/approach: The hypotheses are tested with German survey data and moderated regression analysis. Findings: Teenagers do not underestimate the negative effects of fast food. However, their decision making fails to incorporate existing knowledge on competitive advantages and gives greater weight to customer satisfaction compared with adults. Behavioral differences between teenage and adult consumers result from differences in cognitive development rather than social pressure. Research limitations/implications: As this study uses subjective consumer data from Germany, future research could validate the conclusions with objective behavioral data from various countries. Practical implications: Of importance to fast food restaurant managers, the primary determinants of customer attitudes and intentions are food quality, the public brand image, social recognition, and perceived competitive advantages. By contrast, service quality and perceived value are less influential. Satisfying teenage customers is more important than informing them about competitive advantages. Social implications: The results imply that fast food-related childhood obesity may be caused by lack of rationality rather than peer pressure or lack of knowledge. Originality/value: As an original contribution, the paper compares adolescents' and adults' decision making regarding fast food restaurants and captures the regularly overlooked influences of the public brand image, social recognition, and perceived competitive advantages. © Emerald Group Publishing Limited.

Ohsumi Y.,Tokyo Institute of Technology
Cell Research | Year: 2014

The year of 2013 marked the 50th anniversary of C de Duve's coining of the term "autophagy" for the degradation process of cytoplasmic constituents in the lysosome/vacuole. This year we regretfully lost this great scientist, who contributed much during the early years of research to the field of autophagy. Soon after the discovery of lysosomes by de Duve, electron microscopy revealed autophagy as a means of delivering intracellular components to the lysosome. For a long time after the discovery of autophagy, studies failed to yield any significant advances at a molecular level in our understanding of this fundamental pathway of degradation. The first breakthrough was made in the early 1990s, as autophagy was discovered in yeast subjected to starvation by microscopic observation. Next, a genetic effort to address the poorly understood problem of autophagy led to the discovery of many autophagy-defective mutants. Subsequent identification of autophagy-related genes in yeast revealed unique sets of molecules involved in membrane dynamics during autophagy. ATG homologs were subsequently found in various organisms, indicating that the fundamental mechanism of autophagy is well conserved among eukaryotes. These findings brought revolutionary changes to research in this field. For instance, the last 10 years have seen remarkable progress in our understanding of autophagy, not only in terms of the molecular mechanisms of autophagy, but also with regard to its broad physiological roles and relevance to health and disease. Now our knowledge of autophagy is dramatically expanding day by day. Here, the historical landmarks underpinning the explosion of autophagy research are described with a particular focus on the contribution of yeast as a model organism. © 2014 IBCB, SIBS, CAS All rights reserved.