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Hokkaido University Collection of Scholarly and Academic Papers (135.711 recursos)

HUSCAP (Hokkaido University Collection of Scholarly and Academic Papers) contains peer-reviewed journal articles, proceedings, educational resources and any kind of scholarly works of Hokkaido University.

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  1. Direct extraction of electron parameters from magnetoconductance analysis in mesoscopic ring array structures

    Sawada, A.; Faniel, S.; Mineshige, S.; Kawabata, S.; Saito, K.; Kobayashi, K.; Sekine, Y.; Sugiyama, H.; Koga, T.
    We report an approach for examining electron properties using information about the shape and size of a nanostructure as a measurement reference. This approach quantifies the spin precession angles per unit length directly by considering the time-reversal interferences on chaotic return trajectorieswithin mesoscopic ring arrays (MRAs). Experimentally, we fabricated MRAs using nanolithography in InGaAs quantum wells which had a gate-controllable spin-orbit interaction (SOI). As a result, we observed anOnsager symmetry related to relativistic magnetic fields, which provided us with indispensable information for the semiclassical billiard ball simulation. Our simulations, developed based on the real-space formalism of the weak localization/antilocalization effect...

  2. GeSn/SiGeSn Multiple-Quantum-Well Electroabsorption Modulator With Taper Coupler for Mid-Infrared Ge-on-Si Platform

    Akie, Minami; Fujisawa, Takeshi; Sato, Takanori; Arai, Masakazu; Saitoh, Kunimasa
    We propose a taper coupler electroabsorption modulator (EAM) composed of GeSn/SiCeSn multiple-quantum-well (MQW) on Ge-on-Si platform for mid-infrared (2 mu m) integrated optical active devices. The epitaxial design is performed by calculating the absorption spectra of GeSn/SiGeSn MQW using many-body theory to investigate the extinction characteristics of GeSn MQW waveguides. Two types of taper couplers are considered for connecting Ge-rib waveguide and GeSn-MQW-highmesa waveguide efficiently. One is an adiabatic taper coupler (ATC) type EAM and it is useful for thin Ge-buffer structure in terms of the extinction ratio. Another is a resonant taper coupler (RTC) type EAM and it is...

  3. Image inpainting based on sparse representations with a perceptual metric

    Ogawa, Takahiro; Haseyama, Miki
    This paper presents an image inpainting method based on sparse representations optimized with respect to a perceptual metric. In the proposed method, the structural similarity (SSIM) index is utilized as a criterion to optimize the representation performance of image data. Specifically, the proposed method enables the formulation of two important procedures in the sparse representation problem, ‘estimation of sparse representation coefficients’ and ‘update of the dictionary’, based on the SSIM index. Then, using the generated dictionary, approximation of target patches including missing areas via the SSIM-based sparse representation becomes feasible. Consequently, image inpainting for which procedures are totally derived from...

  4. Visualizing Web Images Using Fisher Discriminant Locality Preserving Canonical Correlation Analysis

    Tateno, Kohei; Ogawa, Takahiro; Haseyama, Miki
    A novel dimensionality reduction method, Fisher Discriminant Locality Preserving Canonical Correlation Analysis (FDLPCCA), for visualizing Web images is presented in this paper. FDLP-CCA can integrate two modalities and discriminate target items in terms of their semantics by considering unique characteristics of the two modalities. In this paper, we focus onWeb images with text uploaded on Social Networking Services for these two modalities. Specifically, text features have high discriminate power in terms of semantics. On the other hand, visual features of images give their perceptual relationships. In order to consider both of the above unique characteristics of these two modalities, FDLPCCA...

  5. Electrical detection of nuclear spin-echo signals in an electron spin injection system

    Lin, Zhichao; Rasly, Mahmoud; Uemura, Tetsuya
    We demonstrated spin echoes of nuclear spins in a spin injection device with a highly polarized spin source by nuclear magnetic resonance (NMR). Efficient spin injection into GaAs from a half-metallic spin source of Co2MnSi enabled efficient dynamic nuclear polarization (DNP) and sensitive detection of NMR signals even at a low magnetic field of similar to 0.1 T and a relatively high temperature of 4.2K. The intrinsic coherence time T-2 of Ga-69 nuclear spins was evaluated from the spin-echo signals. The relation between T-2 and the decay time of the Rabi oscillation suggests that the inhomogeneous effects in our system...

  6. Feasibility of in vivo three-dimensional T-2(*) mapping using dicarboxy-PROXYL and CW-EPR-based single-point imaging

    Kubota, Harue; Komarov, Denis A.; Yasui, Hironobu; Matsumoto, Shingo; Inanami, Osamu; Kirilyuk, Igor A.; Khramtsov, Valery V.; Hirata, Hiroshi
    Objectives The aim of this study was to demonstrate the feasibility of in vivo three-dimensional (3D) relaxation time T-2* mapping of a dicarboxy-PROXYL radical using continuous-wave electron paramagnetic resonance (CW-EPR) imaging. Materials and methods Isotopically substituted dicarboxy-PROXYL radicals, 3,4-dicarboxy-2,2,5,5-tetra(H-2(3)) methylpyrrolidin-( 3,4-H-2(2))-(1-N-15)-1-oxyl (H-2, N-15-DCP) and 3,4-dicarboxy-2,2,5,5-tetra(H-2(3)) methylpyrrolidin-(3,4-H-2(2))1- oxyl (H-2-DCP), were used in the study. A clonogenic cell survival assay was performed with the H-2-DCP radical using squamous cell carcinoma (SCC VII) cells. The time course of EPR signal intensities of intravenously injected H-2, N-15-DCP and H-2-DCP radicals were determined in tumor-bearing hind legs of mice (C3H/HeJ, male, n = 5). CW-EPR-based...

  7. Digitization of natural objects with micro CT and photographs

    Ijiri, Takashi; Todo, Hideki; Hirabayashi, Akira; Kohiyama, Kenji; Dobashi, Yoshinori
    In this paper, we present a three-dimensional (3D) digitization technique for natural objects, such as insects and plants. The key idea is to combine X-ray computed tomography (CT) and photographs to obtain both complicated 3D shapes and surface textures of target specimens. We measure a specimen by using an X-ray CT device and a digital camera to obtain a CT volumetric image (volume) and multiple photographs. We then reconstruct a 3D model by segmenting the CT volume and generate a texture by projecting the photographs onto the model. To achieve this reconstruction, we introduce a technique for estimating a camera...

  8. A 750-MHz Electronically Tunable Resonator Using Microstrip Line Couplers for Electron Paramagnetic Resonance Imaging of a Mouse Tumor-Bearing Leg

    Amida, Tatsuya; Nakaoka, Ririko; Komarov, Denis A.; Yamamoto, Kumiko; Inanami, Osamu; Matsumoto, Shingo; Hirata, Hiroshi
    Objective: The purpose of this work was to develop an electronically tunable resonator operating at 750 MHz for continuous-wave electron paramagnetic resonance (CW-EPR) imaging of a mouse tumor-bearing leg. Methods: The resonator had a multi-coil parallel-gap structure with a sample space of 16 mm in diameter and 20 mm in length. Microstrip line couplers were used in conjunction with varactor diodes to enable resonance frequency adjustment and to reduce the nonlinear effects of the varactor diodes. The resonator was modeled by the finite-element method and a microwave circuit simulation was performed to clarify its radiofrequency characteristics. Results: A tunable resonator...

  9. Graph-Based Video Search Reranking with Local and Global Consistency Analysis

    YOSHIDA, Soh; OGAWA, Takahiro; HASEYAMA, Miki; MUNEYASU, Mitsuji
    Video reranking is an effective way for improving the retrieval performance of text-based video search engines. This paper proposes a graph-based Web video search reranking method with local and global consistency analysis. Generally, the graph-based reranking approach constructs a graph whose nodes and edges respectively correspond to videos and their pairwise similarities. A lot of reranking methods are built based on a scheme which regularizes the smoothness of pairwise relevance scores between adjacent nodes with regard to a user’s query. However, since the overall consistency is measured by aggregating only the local consistency over each pair, errors in score estimation...

  10. An Extended Thin Approximation Method to Simulate Screening Current Induced in REBCO Coils

    Noguchi, So; Hahn, Seungyong; Ueda, Hiroshi; Kim, SeokBeom; Ishiyama, Atsushi
    Superconducting magnets wound with second-generation high-temperature superconductors, i.e., REBa2Cu3O7-x (REBCO, RE = Rare Earth) tapes, are desired to apply high magnetic field nuclear magnetic resonance, MRI, and accelerators. However, a major problem for practical application is an undesirable irregular magnetic field caused by screening currents induced in REBCO tapes. To investigate the screening current-induced magnetic field, a few simulation methods have been proposed. One of the effective simulation methods employs a finite-element method with a thin approximation method. Although the thin approximation method was developed to simulate eddy currents in magnetic steel sheets, and it is not applicable to REBCO...

  11. Helicobacter Pylori infection detection from gastric X-ray images based on feature fusion and decision fusion

    Ishihara, Kenta; Ogawa, Takahiro; Haseyama, Miki
    In this paper, a fully automatic method for detection of Helicobacter pylori (H. pylori) infection is presented with the aim of constructing a computer-aided diagnosis (CAD) system. In order to realize a CAD system with good performance for detection of H. pylori infection, we focus on the following characteristic of stomach X-ray examination. The accuracy of X-ray examination differs depending on the symptom of H. pylori infection that is focused on and the position from which X-ray images are taken. Therefore, doctors have to comprehensively assess the symptoms and positions. In order to introduce the idea of doctors' assessment into...

  12. Synthesis of Equivalent Circuit of Wireless Power Transfer Device Using Homogenization-Based FEM

    Otomo, Yoshitsugu; Sato, Yuki; Fujita, Shogo; Igarashi, Hajime
    In this work, the multi-turn coil used in a wireless power transfer (WPT) device is modeled as a uniform material using the homogenization method to consider the proximity effect. By fitting the coil impedance to the numerical results, the Cauer equivalent circuit of the multi-turn coil is synthesized for design and optimization of the power circuits in the WPT device. It is shown that the results obtained from the equivalent circuit and measurement are in good agreement. Moreover, the impedance of a flat WPT coil composed of a Litz wire is shown to be accurately evaluated by the proposed method...

  13. Eddy Current Analysis of Litz Wire Using Homogenization-Based FEM in Conjunction With Integral Equation

    Hiruma, Shingo; Otomo, Yoshitsugu; Igarashi, Hajime
    A new method is introduced to evaluate the macroscopic permeability of a litz wire which is composed of stranded conductors. In this method, an integral equation is solved for the complex magnetization in the litz wire generated due to the proximity effect. The macroscopic permeability computed from the magnetization is used in the homogenization-based finite-element analysis of eddy currents in a litz-wire coil. It is shown that the wire twist has a little effect on the complex permeability.

  14. Topology Optimization Using Basis Functions for Improvement of Rotating Machine Performances

    Sasaki, Hidenori; Igarashi, Hajime
    This paper presents a new topology optimization method based on basis functions for design of rotating machines. In this method, the core shape of a given rotating machine is represented by the linear combination of the basis functions. The shape is then freely deformed by changing the weighting coefficients to the basis functions to find the optimal shape. The proposed method is compared with the conventional shape optimization based on polygon morphing. The former is shown to outperform the latter in both interior permanent magnet and synchronous motor models.

  15. Finite-Element Analysis of Magnetically Shielded Wire Coils Using Homogenization Method

    Fujita, Shogo; Igarashi, Hajime
    A magnetically shielded wire (MSW), which has magnetic-conductive thin layers on the surface of a wire conductor, is expected to reduce the eddy current losses due to the proximity effect. The conventional finite-element method (FEM) needs unacceptably long computational time to analyze eddy currents in multi-turn MSWs. This paper proposes a homogenization method, which models MSW as a uniform material with complex permeability. The coil impedance evaluated by the homogenization-based FEM with coarse elements is shown to agree well with that obtained by the conventional FEM with much finer elements. Moreover, the optimal shield thickness is determined by the proposed...

  16. Virtual phase conjugation based optical tomography for single-shot three-dimensional imaging

    Goto, Yuta; Okamoto, Atsushi; Shibukawa, Atsushi; Ogawa, Kazuhisa; Tomita, Akihisa
    We propose a virtual phase conjugation (VPC) based optical tomography (VPC-OT) for realizing single-shot optical tomographic imaging systems. Using a computer-based numerical beam propagation, the VPC combines pre-modulation and post-demodulation of the probe beam's wavefront, which provides an optical sectioning capability for resolving the depth coordinates. In VPC-OT, the physical optical microscope system and VPC are coupled using digital holography. Therefore, in contrast to conventional optical tomographic imaging (OTI) systems, this method does not require additional elements such as low-coherence light sources or confocal pinholes. It is challenging to obtain single-shot three-dimensional (3D) tomographic images using a conventional OTI system;...

  17. An energy-efficient dynamic branch predictor with a two-clock-cycle naive Bayes classifier for pipelined RISC microprocessors

    Hida, Itaru; Takamaeda-Yamazaki, Shinya; Ikebe, Masayuki; Motomura, Masato; Asai, Tetsuya
    In this paper, we propose a Bayesian branch-prediction circuit, consisting of an instruction-feature extractor and a naive Bayes classifier (NBC), as a machine learning approach for branch prediction. A branch predictor predicts the outcome of a branch instruction by analyzing the pattern of the previous branch outcome. In other words, branch prediction can be viewed as a type of pattern recognition problem, and such problems are often solved using neural networks. A perceptron branch predictor has already been proposed as one example of a neural branch prediction architecture, which predicts the next branch outcome by using past branch history to...

  18. A relaxation-accelerated propagator method for calculations of electron energy distribution function and electron transport parameters in gas under dc electric fields

    Sugawara, Hirotake
    A propagator method (PM), a numerical technique to solve the Boltzmann equation (BE) for the electron velocity or energy distribution function (EVDF/EEDF) of electron swarms in gases, was customized to obtain the equilibrium solution quickly. The PM calculates the number of electrons in cells defined in velocity space using an operator called the propagator or Green’s function. The propagator represents the intercellular transfer of electrons corresponding to the electron velocity change due to the acceleration by the electric field and the collisional events with gas molecules. The relaxation of the EVDF to its drift equilibrium solution proceeds with iterative propagator...

  19. 生理機能及び代謝イメージングによるがん治療効果の予測

    Matsumoto, Shingo
    Tumors develop a characteristic microenvironment depending on their specific genetic mutations. The direct products of mutant genes and the resulting microenvironmental changes provoke metabolic changes in the tumor. If noninvasive imaging techniques including magnetic resonance imaging (MRI) could be used to detect such microenvironmental and metabolic changes in tumors, we might be able to provide more effective treatment strategies for individual tumors in patients. In addition to conventional imaging techniques, this review article introduces quantitative 3D oxygen imaging using electron paramagnetic resonance imaging (EPRI) and hyperpolarized (13)C metabolic MRI and shows how these imaging techniques can help to monitor and...

  20. Quantum key distribution with an efficient countermeasure against correlated intensity fluctuations in optical pulses

    Yoshino, Ken-ichiro; Fujiwara, Mikio; Nakata, Kensuke; Sumiya, Tatsuya; Sasaki, Toshihiko; Takeoka, Masahiro; Sasaki, Masahide; Tajima, Akio; Koashi, Masato; Tomita, Akihisa
    Quantum key distribution (QKD) allows two distant parties to share secret keys with the proven security even in the presence of an eavesdropper with unbounded computational power. Recently, GHz-clock decoy QKD systems have been realized by employing ultrafast optical communication devices. However, security loopholes of high-speed systems have not been fully explored yet. Here we point out a security loophole at the transmitter of the GHz-clock QKD, which is a common problem in high-speed QKD systems using practical band-width limited devices. We experimentally observe the inter-pulse intensity correlation and modulation pattern-dependent intensity deviation in a practical high-speed QKD system. Such...

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