Junichiro Shiomi

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

We demonstrate successful application of first-principles-based thermal conductivity calculation on half-Heusler compounds that are promising, environmentally friendly thermoelectric materials. Taking the case of a $p$-type half-Heusler structure, the harmonic and anharmonic interatomic force constants were obtained from a set of force-displacement data calculated by the density functional theory. Thermal conductivity was obtained by two different methods: (1) Boltzmann-Peierls formula with phon

We computationally designed an ultranarrow-band wavelength-selective thermal radiator via a materials informatics method alternating between Bayesian optimization and thermal electromagnetic field calculation. For a given target infrared wavelength, the optimal structure was efficiently identified from over 8 billion candidates of multilayers consisting of multiple components (Si, Ge, and SiO₂). The resulting optimized structure is an aperiodic multilayered metamaterial exhibiting hig

Artificially structured thermal metamaterials provide an unprecedented possibility of molding heat flow that is drastically distinct from the conventional heat diffusion in naturally conductive materials. The Laplacian nature of heat conduction makes the transformation thermotics, as a design principle for thermal metadevices, compatible with transformation optics. Various functional thermal devices, such as thermal cloaks, concentrators, and rotators, have been successfully demonstrated. How fa

The diffusive-ballistic heat conduction of finite-length single-walled carbon nanotubes has been studied by means of nonequilibrium molecular dynamics simulations. The length dependence of thermal conductivity is quantified for a range of nanotube lengths up to 1.6 µm at room temperature. A gradual transition from nearly pure ballistic to diffusive-ballistic heat conduction was identified from the thermal conductivity profile. In the diffusive-ballistic regime, the profile exhibits power-law len

Thermal boundary conductance is typically positively correlated with interfacial adhesion at the interface. Here, we demonstrate a counterintuitive experimental result in which a weak van der Waals interface can give a higher thermal boundary conductance than a strong covalently bonded interface. This occurs in a system with highly mismatched vibrational frequencies (copper/diamond) modified by a self-assembled monolayer. Using finely controlled fabrication and detailed characterization, complem

Wavelength-selective thermal emitters (WS-TEs) have been frequently designed to achieve desired target emissivity spectra, as a typical emissivity engineering, for broad applications such as thermal camouflage, radiative cooling, and gas sensing, etc. However, previous designs require prior knowledge of materials or structures for different applications and the designed WS-TEs usually vary from applications to applications in terms of materials and structures, thus lacking of a general design fr