Akihiko Hirata

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Grain rotation is a well-known phenomenon during high (homologous) temperature deformation and recrystallization of polycrystalline materials. In recent years, grain rotation has also been proposed as a plasticity mechanism at low temperatures (for example, room temperature for metals), especially for nanocrystalline grains with diameter d less than ~15 nm.(More)
A 120-GHz-band close-proximity wireless system that achieves the first 10-Gbit/s real-time transmission satisfying the regulation for extremely low-power radio stations (ELRS regulation). The use of photonic technologies enables the transmitter to perform 10-Gbit/s quadrature-phase-shift keying (QPSK) modulation and generate an RF spectrum with negligibly(More)
This paper presents a 120-GHz-band 10-Gbit/s quadrature phase-shift-keying (QPSK) modulator and demodulator. To reduce system complexity, the modulator employs direct modulation, and the demodulator uses differentially coherent detection. We fabricated the modulator monolithic microwave integrated circuit (MMIC) and demodulator MMIC with 0.1-μm-gate(More)
Precipitate size and number density are two key factors for tailoring the mechanical behavior of nanoscale precipitate-hardened alloys. However, during thermal aging, the precipitate size and number density change, leading to either poor strength or high strength but significantly reduced ductility. Here we demonstrate, by producing nanoscale(More)
The elastic strain sustainable in crystal lattices is usually limited by the onset of inelastic yielding mediated by discrete dislocation activity, displacive deformation twinning and stress-induced phase transformations, or fracture associated with flaws. Here we report a continuous and gradual lattice deformation in bending nickel nanowires to a(More)
SUMMARY We present a low-phase-noise and frequency-tunable pho-tonic millimeter-wave (MMW) generator based on two-mode beating. The generator consists of a single-mode laser, an external optical intensity mod-ulator, and a planar lightwave circuit (PLC) on which an arrayed-waveguide grating (AWG) and 3-dB optical combiners are integrated. Because the AWG(More)
This paper describes a 10-Gbit/s fully integrated wireless link for last-one-mile access in optical fiber networks. The wireless equipment employs quadrature phase-shift keying (QPSK) for modulation. The transmitter (TX) head of the link includes a 120-GHz-band QPSK TX module and an encoder board for generating an in-phase and quadrature signal from a(More)
—This paper presents a three-dimensional (3-D) localization system for ultra-wideband (UWB) impulsive noise sources. The localization algorithm is in terms of time difference of arrival (TDOA). Firstly, a feasibility study of the 3-D localization scheme is carried out numerically. Then, the effectiveness and limitation of the scheme are revealed. Our(More)
Solid silicon monoxide is an amorphous material which has been commercialized for many functional applications. However, the amorphous structure of silicon monoxide is a long-standing question because of the uncommon valence state of silicon in the oxide. It has been deduced that amorphous silicon monoxide undergoes an unusual disproportionation by forming(More)