Hokkaido University Collection of Scholarly and Academic Papers
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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.
Mostrando recursos 1 - 20 de 274
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Timesaving techniques for decision of electron–molecule collisions in Monte Carlo simulation of electrical discharges - Sugawara, Hirotake; Mori, Naoki; Sakai, Yosuke; Suda, Yoshiyuki
Techniques to reduce the computational load for determination of electron–molecule collisions in Monte Carlo simulations of electrical discharges have been presented. By enhancing the detection efficiency of the no-collision case in the decision scheme of the collisional events, we can decrease the frequency of access to time-consuming subroutines to calculate the electron collision cross sections of the gas molecules for obtaining the collision probability. A benchmark test and an estimation to evaluate the present techniques have shown a practical timesaving efficiency.
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Control of surfaces and heterointerfaces of AlGaN/GaN system for sensor devices and their on-chip integration on nanostructures - Hasegawa, Hideki
For successful construction of sensor devices and their future on-chip integration on nanostructures, this paper discusses the present status of understanding and control of surfaces and heterointerfaces of the AlGaN/GaN material system by reviewing a series of works recently carried out by the authors’ group.
Leakage currents in Schottky contacts are explained by the authors’ thin surface barrier (TSB) model. An important role is played by oxygen shallow donors in leakage in AlGaN Schottky diodes. A large leakage reduction has been achieved by a novel surface control process for oxygen gettering. An unprecedented high sensitivity has been obtained in AlGaN/GaN Schottky...
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Children construct novel word meaning ad-hoc based on known words : Computational model of shape and material biases - Kurosaki, Kosuke; Omori, Takashi
Taking the stance that two well-known word learning biases (shape and material bias) are formed through learning (learned bias account, LBA), we illustrated a concrete computational mechanism with "ad-hoc meaning substitution (AMS)" hypothesis, and verified it by two computer simulations. AMS represents that when given a novel word and a corresponding instance, children create novel word meaning by using the known word meaning and the instance as an ad-hoc template. The AMS function enables fast mapping and vocabulary spurt. To describe the AMS process computationally, we introduced "word distributional prototype (WDP)," which is the explicit representation of word meaning with...
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Ad-hoc Meaning Substitution Causes Shape and Material Biases : Computational Explanation for Emergence of Word Learning Biases - Kurosaki, Kosuke; Omori, Takashi
We illustrated a computational mechanism of shape bias and material bias with "ad-hoc meaning substitution (AMS)" hypothesis and verified it by computer simulations. AMS represents that when given a novel word and a instance object/substance, children substitute a known noun meaning nearest to the instance and the instance itself as an ad-hoc template of the novel noun meaning. The substitution enables fast mapping and subsequent vocabulary spurt. To describe internal process of AMS, we introduced "word distributional prototype (WDP)" as an explicit representation of word meaning with an inductive learning function. Simulation 1 revealed that when neural networks with WDP...
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Topology Optimization Based on Immune Algorithm and Multigrid Method - Watanabe, K.; Campelo, F.; Igarashi, H.
This paper describes topology optimization of electromagnetic systems using the multigrid method. The topology optimization employs uniform rectangular finite elements, in which the multigrid method works effectively as a fast linear solver. Moreover, the present method uses a new optimization algorithm, based on the artificial immune systems paradigm, in which the multilevel search is carried out
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Coupling between structural deformation and attitude motion of large planar space structures suspended by multi-tethers - Ishimura, Kosei; Higuchi, Ken
A planar space structure suspended by multi-tethers is one candidate for large and lightweight structures. For such flexible structures, coupling phenomena between structural deformation and attitude motion must be considered. In the present paper, the dynamic characteristics of a planar structure suspended by multi-tethers are investigated. Simulation results reveal that the coupling occurs for low tether stiffness. In addition, it is shown that the coupling can also occur if a number of the tethers become slack. Thermal deformation of the planar structure is one cause of tether slack. Thermal deformation and the induced attitude motion are also investigated. It is...
7.
Measurement of chromatic dispersion and Raman gain efficiency of a hole-assisted fiber : Influence of bend - Varshney, S. K.; Tsuchida, Y.; Sasaki, K.; Saitoh, K.; Koshiba, M.
We have experimentally measured the Raman gain efficiency (RGE) and chromatic dispersion (CD) of a hole-assisted fiber (HAF). The RGE of a HAF was characterized using standard pump on/off technique while the CD of the fiber was measured using optical network analyzer. Theoretical simulations of the modal characteristics and the RGE of HAF were carried out using an accurate full-vectorial finite element method. Further, the bending effects on the CD and the RGE of a HAF with a smallest feasible bending radius are demonstrated. It was found that the CD increases while the RGE is decreased by bending HAF in...
8.
Effect of a MgO interlayer on the structural and magnetic properties of Co[sub 2]Cr[sub 0.6]Fe[sub 0.4]Al thin films epitaxially grown on GaAs substrates - Yano, T.; Uemura, T.; Matsuda, K.-i.; Yamamoto, M.
The effect of a MgO interlayer on the structural and magnetic properties of Co2Cr0.6Fe0.4Al (CCFA) thin films epitaxially grown on GaAs substrates by sputtering was investigated. When the MgO interlayer thickness was 1.0 nm or less, the CCFA films were grown with a cube-on-cube relation to GaAs and no significant decrease in either the x-ray diffraction intensity or saturation magnetization was observed. In contrast, when the MgO thickness was 1.5 nm or more, the CCFA film was rotated by 45° in the (001) plane with respect to GaAs, and both the x-ray diffraction intensity and saturation magnetization decreased. All samples...
9.
Design of effectively single-mode air-core photonic bandgap fiber with improved transmission characteristics for the realization of ultimate low loss waveguide - Murao, Tadashi; Saitoh, Kunimasa; Florous, Nikolaos J.; Koshiba, Masanori
In this paper, we study the novel propagation properties of an improved triangular-type air-core photonic bandgap fiber (PBGF) structured with an anti-resonant silica core surround, through a full-vector modal solver based on the finite-element method (FEM). At first, to realize a single-mode operation over a wide wavelength range, the fiber whose core is constructed by removing 1 air-hole and expanded is proposed and structurally-optimized. In particular, the structural parameters for the fiber that prevent the narrow-band transmission due to the existence of the surface modes and enhance the confinement of the power in the air-core are presented. For the realization...
10.
CMOS Smart Sensor for Monitoring the Quality of Perishables - Ueno, K.; Hirose, T.; Asai, T.; Amemiya, Y.
We developed a CMOS integrated-circuit sensor to monitor the change in quality of perishables that depends on surrounding temperatures. Our sensor makes use of the fact that the temperature dependence of the subthreshold current in MOSFETs is analogous to that of the degradation of perishables. The sensor is attached to perishable goods such as farm and marine products and is distributed from producers to consumers along with the goods. During their distribution process, the sensor measures the surrounding temperatures and emulates the degradation of the goods caused by the temperature. By reading the output of the sensor, consumers can determine...
11.
Numerical Modeling of Cryogenic Temperature Sensors Based on Plasmonic Oscillations in Metallic Nanoparticles Embedded Into Photonic Crystal Fibers - Florous, Nikolaos John; Saitoh, Kunimasa; Koshiba, Masanori
We perform a numerical investigation on the operation of an inline temperature sensor based on the inclusion of metallic nanoparticles into photonic crystal fibers (PCFs). This creates a simple, yet robust, platform which can be used to investigate the properties of nanoparticles, for sensing, spectroscopy, and optical switching applications. The optical response of gold nanoparticles embedded in the PCF matrix was evaluated as a function of temperature and the use of the structure as an inline fiber-optic temperature sensor is theoretically described. A blue-shift in the localized surface plasmon resonance related peak, as well as narrowing of the plasmon resonance,...
12.
Power-law behavior and condensation phenomena in disordered urn models - Inoue, Jun-ichi; Ohkubo, Jun
We investigate equilibrium statistical properties of urn models with disorder. Two urn models are proposed; one belongs to the Ehrenfest class, and the other corresponds to the Monkey class. These models are introduced from the view point of the power-law behavior and randomness; it is clarified that quenched random parameters play an important role in generating power-law behavior. We evaluate the occupation probability P(k) with which an urn has k balls by using the concept of statistical physics of disordered systems. In the disordered urn model belonging to the Monkey class, we find that above critical density ρc for a...
13.
Changes in the spontaneous calcium oscillations for the development of the preconditioning-induced ischemic tolerance in neuron/astrocyte co-culture. - Tanaka, Motoki; Kawahara, Koichi; Kosugi, Tatsuro; Yamada, Takeshi; Mioka, Tetsuo
Spontaneous Ca2+ oscillations are believed to contribute to the regulation of gene expression. Here we investigated whether and how the dynamics of Ca2+ oscillations changed after sublethal preconditioning (PC) for PC-induced ischemic tolerance in neuron/astrocyte co-cultures. The frequency of spontaneous Ca2+ oscillations significantly decreased between 4 and 8 h after the end of PC in both neurons and astrocytes. Treatment with 2-APB, an inhibitor of IP3 receptors, decreased the oscillatory frequency, induced ischemic tolerance and a down-regulation of glutamate transporter GLT-1 contributing to the increase in the extracellular glutamate during ischemia. The expression of GLT-1 is known to be up-regulated...
14.
A Wide-Dynamic-Range Compression Image Sensor With Negative-Feedback Resetting - Ikebe, M.; Saito, K.
A CMOS image sensor capable of wide-dynamic-range compression is proposed. This sensor has two main features. It uses a negative-feedback technique to set any intermediate voltage into photodiode (PD) capacitance in the pixel circuit. It also uses a quasi-holding function by resetting the pixel-output voltage into PD capacitance. Dynamic range compression is achieved by individually selecting pixels and by setting an intermediate voltage or performing quasi-holding with respect to each pixel. Output data has a polygon-like form corresponding to a change from high sensitivity to low sensitivity as optical intensity becomes stronger. Experimental results obtained with a chip fabricated using...
15.
Fabrication of Fully Epitaxial Co2Cr0.6Fe0.4Al/MgO/Co2Cr0.6Fe0.4Al Magnetic Tunnel Junctions - Marukame, T.; Ishikawa, T.; Hakamata, S.; Matsuda, K.-I.; Uemura, T.; Yamamoto, M.
Fully epitaxial magnetic tunnel junctions (MTJs) of Co2Cr0.6Fe0.4Al (CCFA)/MgO/CCFA with exchange biasing were fabricated. The fabricated MTJs showed clear exchange-biased tunnel magnetoresistance (TMR) characteristics due to the CCFA/Ru/Co90Fe10/IrMn exchange-biased synthetic ferrimagnetic layer. The TMR characteristics were investigated as a function of in situ annealing temperature (Ta) for the upper CCFA layer. We obtained TMR ratios of 60% at room temperature (RT) and 238% at 4.2 K for MTJs with Ta of 400 degC, while those for MTJs with Ta of RT (i.e., having an as-deposited upper CCFA layer) were 17% at RT and 80% at 4.2 K. These results clearly...
16.
Four-State Magnetoresistance in Epitaxial CoFe-Based Magnetic Tunnel Junctions - Uemura, T.; Marukame, T.; Matsuda, K.; Yamamoto, M.
A four-state magnetic random access memory (MRAM) was developed using an epitaxial Co50Fe50-MgO-Co50Fe 50 magnetic tunnel junction (MTJ) with a tunnel magnetoresistance (TMR) ratio of 145% at room temperature (RT). Four remanent magnetization states in the single-crystalline Co50Fe50 electrode, due to the cubic anisotropy with easy axes of the lang110rang directions, result in four possible angular-dependent TMRs, each separated by more than 20% at RT. Analysis of the asteroid curve for Co50Fe50 indicated that the magnetic field along 22.5deg from the lang110rang directions made it possible to change the magnetization direction of the selected cell without disturbing those of the...
17.
Fluctuations in time intervals of financial data from the view point of the Gini index - Sazuka, Naoya; Inoue, Jun-ichi
We propose an approach to explain fluctuations in time intervals of financial markets data from the view-point of the Gini index. We show the explicit form of the Gini index for a Weibull distribution: A good candidate to describe the first passage time of foreign exchange rate. The analytical expression of the Gini index compares well with the value obtained from empirical data.
18.
Crossover between Lévy and Gaussian regimes in first-passage processes - Inoue, Jun-ichi; Sazuka, Naoya
We propose an approach to the problem of the first-passage time. Our method is applicable not only to the Wiener process but also to the non-Gaussian Lévy flights or to more complicated stochastic processes whose distributions are stable. To show the usefulness of the method, we particularly focus on the first-passage time problems in the truncated Lévy flights (the so-called KoBoL processes from Koponen, Boyarchenko, and Levendorskii), in which the arbitrarily large tail of the Lévy distribution is cut off. We find that the asymptotic scaling law of the first-passage time t distribution changes from t−(+1)/-law (non-Gaussian Lévy regime) to...
20.
3D topology optimization using an immune algorithm - Campelo, Felipe; Watanabe, Kota; Igarashi, Hajime
Purpose: The paper introduces an evolutionary algorithm based on the artificial immune systems paradigm for topology optimization (TO) in 3D. Design/methodology/approach: The 3D TO algorithm is described, and experimentally validated on an electromagnetic design problem. Findings: The proposed method is capable of finding an optimal configuration for the validation problem used. Research limitations/implications: More tests are needed in order to fully assert the capabilities of the algorithm. Moreover, further improvements are needed in order to obtain smoother topologies at the end of the optimization procedure. Practical implications: The paper presents a novel tool for the design of electromagnetic devices, using...
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