| 1. |
- Alekseev, A. Y., et al.
(author)
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Structural stability and electronic properties of 2D alkaline-earth metal silicides, germanides, and stannides
- 2020
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In: Japanese Journal of Applied Physics. - : IOP PUBLISHING LTD. - 0021-4922 .- 1347-4065. ; 59
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Research review (peer-reviewed)abstract
- We present the results of an extended theoretical study of the structure, phonon, electronic and optical properties of 2D alkaline-earth metal silicides, germanides and stannides (2D Me2X, where Me=Mg, Ca, Sr, Ba and X=Si, Ge, Sn). The performed analysis has shown the occurrence of the pseudo passivation effect and ionic chemical bonding in these 2D Me2X. In addition, the preformed investigation of their phonon spectra has shown the absence of imaginary frequencies indicating the stability of these 2D structures. The band structure calculations performed using the hybrid functional have revealed that all 2D Me2X are semiconductors with the gap varying from 0.12 to 1.01 eV. Among them Mg- and Ca-based 2D materials are direct band-gap semiconductors with the first direct transition having appreciable oscillator strength. We also propose to consider ternary 2D silicides, germanides and stannides with different Me atoms as a feasible way to modify properties of parent 2D Me2X.
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| 2. |
- Mozumi, Michiya, et al.
(author)
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Anti-Aliasing method for ultrasonic 2D phase-sensitive motion estimator
- 2020
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In: Japanese Journal of Applied Physics. - : IOP Publishing. - 0021-4922 .- 1347-4065. ; 59:SK
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Journal article (peer-reviewed)abstract
- A 2D motion estimator can estimate tissue motions and blood flow dynamics more accurately than a 1D motion estimator. In this study, we proposed a simple anti-Aliasing filter to unwrap the phase of the cross spectrum. The proposed method is evaluated by simulation mimicking steady flows, and the magnitude of the true velocity was changed from 200 to 2400 mm s-1. In the simulation, bias error was improved from 295.0% to 4.9% by the proposed method at a true velocity magnitude of 1600 mm s-1. Also, in the in vivo measurement of the left ventricle, the wrapping in the phase of the cross spectrum was corrected by the proposed method, and the directions of the blood velocity vectors were estimated more accurately.
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| 3. |
- Mozumi, Michiya, et al.
(author)
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Impact of spacing of ultrasound receiving beams on estimation of 2D motion velocity
- 2021
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In: Japanese Journal of Applied Physics. - : IOP Publishing. - 0021-4922 .- 1347-4065. ; 60:SD
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Journal article (peer-reviewed)abstract
- For more detailed measurement of cardiovascular motion and complex blood flow, a two-dimensional (2D) velocity estimation method is required in functional ultrasound imaging. The block matching method based on the correlation function is one of the standard 2D motion estimators. In this study, we investigated the effect of lateral sampling intervals of an ultrasonic B-mode image on the accuracy in velocity estimation. In simulation, bias error (BE) in estimated velocities became -13% with an ultrasonic center frequency of 7.5 MHz and spacings of receiving beams of 0.2 mm. Such a BE was improved from -13% to -1.4% by changing the spacings from 0.2 to 0.1 mm. In the in vivo experiment, the maximum velocity obtained with spacings of 0.2 mm was underestimated by -16% as compared to those obtained with 0.1 mm. Hence, the trend was similar to that in the simulation.
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| 4. |
- Nagaoka, Ryo, et al.
(author)
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Basic study on estimation method of wall shear stress in common carotid artery using blood flow imaging
- 2020
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In: Japanese Journal of Applied Physics. - : IOP Publishing. - 0021-4922 .- 1347-4065. ; 59
-
Journal article (peer-reviewed)abstract
- In this paper, we propose a method for adaptive selection of the kernel size used in estimation of the wall shear stress (WSS) based on flow velocity profiles obtained by the blood flow imaging method based on enhancement of RF echo signals from blood cells using a singular value decomposition based clutter filter. Two simulation phantom experiments with the Field II program were performed to validate the proposed method. In the simulation experiments, the average bias error (BE) between the WSSs estimated by the conventional method and theoretical one was 16.5%. The proposed method could reduce the average BE to 12.3%. Also, the proposed method was applied to RF echo signals from a common carotid artery (CCA) of a healthy male subject. The WSSs in the CCA were estimated during one cardiac cycle and in a range similar to that in previous reports.
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| 5. |
- Shukla, K, et al.
(author)
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Finite element simulation of transmission and reflection of acoustic waves in the ultrasonic transducer
- 2022
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In: JAPANESE JOURNAL OF APPLIED PHYSICS. - : IOP Publishing. - 0021-4922 .- 1347-4065. ; 61:SG
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Journal article (other academic/artistic)abstract
- In scanning acoustic microscopy (SAM), the image quality depends on several factors such as noise level, resolution, and interaction of the waves with sample boundaries. The theoretical equations for the reflection coefficient and transmission coefficient are suitable for plane boundaries but fail for curved/rough boundaries. We presented a finite element method-based modeling for the loss coefficients in SAM. A focused and unfocused lens with a flat object, furthermore a focused lens with a curved object was selected for loss coefficients calculation. The loss calculation in terms of energy for defining the acoustic reflection and transmission losses and its dependence on the radius of curvature of the test object has also been presented.
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| 6. |
- Jansson, Maria, et al.
(author)
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Nanoplatelet interactions in the presence of multivalent ions : The effect of overcharging and stability
- 2020
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In: Journal of Colloid and Interface Science. - : Elsevier BV. - 0021-9797. ; 579, s. 573-581
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Journal article (peer-reviewed)abstract
- Hypothesis: The stability of colloidal dispersions in the presence of multivalent ions depends strongly on the electrostatic interactions between the suspended particles. Of particular interest are colloidal particles having dimensions in the nanometric range and with an anisotropic shape due to its high surface area per unit mass, for example clay, which has the key characteristic of a negatively charged surface, surrounded by an oppositely charged rim. Experiments: In this study, we investigate the interactions in nanoplatelet dispersions for the model system of Laponite® clay with addition of mono- and multivalent salt. Molecular dynamics simulations with enhanced umbrella sampling have been utilised in combination with the experimental techniques of zeta-potential measurements, dynamic light scattering, and transmission electron microscopy. Findings: It was observed that tactoid formation and tactoidal dissolution due to overcharging occur upon the addition of trivalent salt. The overcharging effect was captured from calculated potential of mean force and confirmed from the zeta-potential, which changed sign from negative to positive when increasing the stoichiometric charge-ratio between the positive salt ions and the clay. Consequently, the gained information could provide useful physical insight of nanoplatelet interactions in the presence of multivalent ions.
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