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Junichiro Shiomi

Bio: Junichiro Shiomi is an academic researcher from University of Tokyo. The author has contributed to research in topics: Thermal conductivity & Carbon nanotube. The author has an hindex of 47, co-authored 271 publications receiving 7212 citations. Previous affiliations of Junichiro Shiomi include National Presto Industries & Royal Institute of Technology.


Papers
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Journal ArticleDOI
TL;DR: In this paper, a single-walled carbon nanotube was investigated by applying a local heat pulse with duration of subpicoseconds, where the heat pulse was generated as coherent fluctuations by connecting a thermostat to the local cell.
Abstract: Nonstationary heat conduction in a single-walled carbon nanotube was investigated by applying a local heat pulse with duration of subpicoseconds. The investigation was based on classical molecular dynamics simulations, where the heat pulse was generated as coherent fluctuations by connecting a thermostat to the local cell for a short duration. The heat conduction through the nanotube was observed in terms of spatiotemporal temperature profiles. Results of the simulations exhibit non-Fourier heat conduction where a distinct amount of heat is transported in a wavelike form. The geometry of carbon nanotubes allows us to observe such a phenomenon in the actual scale of the material. The resulting spatiotemporal profile was compared with the available macroscopic equations, the so-called non-Fourier heat conduction equations, in order to investigate the applicability of the phenomenological models to a quasi-one-dimensional system. The conventional hyperbolic diffusion equation fails to predict the heat conduction due to the lack of local diffusion. It is shown that this can be remedied by adopting a model with dual relaxation time. Further modal analyses using wavelet transformations reveal a significant contribution of the optical phonon modes to the observed wavelike heat conduction. The result suggests that, in carbon nanotubes with finite length where the long-wavelength acoustic phonons behave ballistically, even optical phonons can play a major role in the non-Fourier heat conduction.

233 citations

Journal ArticleDOI
TL;DR: In this article, a lower thermal conductivity in p-type half-Heuslers was achieved when Ti is used to replace Zr, i.e., Hf1−xTixCoSb0.8Sn0.2, due to larger differences in the atomic mass and size between Hf and Ti.
Abstract: High lattice thermal conductivity has been the bottleneck for further improvement of the thermoelectric figure-of-merit (ZT) of half-Heuslers (HHs) Hf1−xZrxCoSb0.8Sn0.2. Theoretically, the lattice thermal conductivity can be reduced by exploring larger differences in the atomic mass and size in the crystal structure, leading to higher ZT. In this paper, we experimentally demonstrated that a lower thermal conductivity in p-type half-Heuslers can be achieved when Ti is used to replace Zr, i.e., Hf1−xTixCoSb0.8Sn0.2, due to larger differences in the atomic mass and size between Hf and Ti compared with Hf and Zr. The highest ZT peak, ∼1.0 at 800 °C, in the Hf1−xTixCoSb0.8Sn0.2 (x = 0.1, 0.2, 0.3, and 0.5) system was achieved using Hf0.8Ti0.2CoSb0.8Sn0.2, which makes this material useful in power generation applications.

231 citations

Journal ArticleDOI
21 Jun 2019
TL;DR: In this paper, the authors demonstrate the successful discovery of new polymers with high thermal conductivity, inspired by machine-learning-assisted polymer chemistry, using a molecular design algorithm trained to recognize quantitative structure.
Abstract: The use of machine learning in computational molecular design has great potential to accelerate the discovery of innovative materials. However, its practical benefits still remain unproven in real-world applications, particularly in polymer science. We demonstrate the successful discovery of new polymers with high thermal conductivity, inspired by machine-learning-assisted polymer chemistry. This discovery was made by the interplay between machine intelligence trained on a substantially limited amount of polymeric properties data, expertise from laboratory synthesis and advanced technologies for thermophysical property measurements. Using a molecular design algorithm trained to recognize quantitative structure—property relationships with respect to thermal conductivity and other targeted polymeric properties, we identified thousands of promising hypothetical polymers. From these candidates, three were selected for monomer synthesis and polymerization because of their synthetic accessibility and their potential for ease of processing in further applications. The synthesized polymers reached thermal conductivities of 0.18–0.41 W/mK, which are comparable to those of state-of-the-art polymers in non-composite thermo-plastics.

217 citations

Journal Article
TL;DR: In this article, a lower thermal conductivity in p-type half-Heuslers was achieved when Ti is used to replace Zr, i.e., Hf1−xTixCoSb0.8Sn0.2, due to larger differences in the atomic mass and size between Hf and Ti.
Abstract: High lattice thermal conductivity has been the bottleneck for further improvement of the thermoelectric figure-of-merit (ZT) of half-Heuslers (HHs) Hf1−xZrxCoSb0.8Sn0.2. Theoretically, the lattice thermal conductivity can be reduced by exploring larger differences in the atomic mass and size in the crystal structure, leading to higher ZT. In this paper, we experimentally demonstrated that a lower thermal conductivity in p-type half-Heuslers can be achieved when Ti is used to replace Zr, i.e., Hf1−xTixCoSb0.8Sn0.2, due to larger differences in the atomic mass and size between Hf and Ti compared with Hf and Zr. The highest ZT peak, ∼1.0 at 800 °C, in the Hf1−xTixCoSb0.8Sn0.2 (x = 0.1, 0.2, 0.3, and 0.5) system was achieved using Hf0.8Ti0.2CoSb0.8Sn0.2, which makes this material useful in power generation applications.

217 citations


Cited by
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01 May 1993
TL;DR: Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems.
Abstract: Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

29,323 citations

28 Jul 2005
TL;DR: PfPMP1)与感染红细胞、树突状组胞以及胎盘的单个或多个受体作用,在黏附及免疫逃避中起关键的作�ly.
Abstract: 抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1(PfPMP1)与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用,在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员,通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

18,940 citations

Journal ArticleDOI
20 Sep 2012-Nature
TL;DR: It is shown that heat-carrying phonons with long mean free paths can be scattered by controlling and fine-tuning the mesoscale architecture of nanostructured thermoelectric materials, and an increase in ZT beyond the threshold of 2 highlights the role of, and need for, multiscale hierarchical architecture in controlling phonon scattering in bulk thermoeLECTrics.
Abstract: Controlling the structure of thermoelectric materials on all length scales (atomic, nanoscale and mesoscale) relevant for phonon scattering makes it possible to increase the dimensionless figure of merit to more than two, which could allow for the recovery of a significant fraction of waste heat with which to produce electricity.

3,670 citations

01 Jan 2011

2,117 citations

Journal ArticleDOI
TL;DR: ShengBTE is a software package for computing the lattice thermal conductivity of crystalline bulk materials and nanowires with diffusive boundary conditions based on a full iterative solution to the Boltzmann transport equation.

1,834 citations