Shingo Hirano 교수

We perform a large set of radiation hydrodynamics simulations of primordial star formation in a fully cosmological context. Our statistical sample of 100 First Stars show that the first generation of stars have a wide mass distribution M_popIII = 10 ~ 1000 M_sun. We first run cosmological simulations to generate a set of primordial star-forming gas clouds. We then follow protostar formation in each gas cloud and the subsequent protostellar evolution until the gas mass accretion onto the protosta

We perform a large set of cosmological simulations of early structure formation and follow the formation and evolution of 1540 star-forming gas clouds to derive the mass distribution of primordial stars. The star formation in our cosmological simulations is characterized by two distinct populations, the so-called Population III.1 stars and primordial stars formed under the influence of far ultraviolet (FUV) radiation (Population III.2D stars). In this work, we determine the stellar masses by usi

The origin of super-massive black holes in the early universe remains poorly understood. Gravitational collapse of a massive primordial gas cloud is a promising initial process, but theoretical studies have difficulty growing the black hole fast enough. We report numerical simulations of early black hole formation starting from realistic cosmological conditions. Supersonic gas motions left over from the Big Bang prevent early gas cloud formation until rapid gas condensation is triggered in a pro

The initial mass function of the first, Population III (Pop III), stars plays a vital role in shaping galaxy formation and evolution in the early Universe. One key remaining issue is the final fate of secondary protostars formed in the accretion disc, specifically whether they merge or survive. We perform a suite of hydrodynamic simulations of the complex interplay between fragmentation, protostellar accretion, and merging inside dark matter minihaloes. Instead of the traditional sink particle m

We report the realization of a low-temperature aqueous pathway for the chemical synthesis of zinc oxide (ZnO) nanowires with low defect density and their room-temperature ultraviolet lasing behavior at low pump fluence. The concentration of solutes determined not only the size of individual nanowires, which influences their optical waveguiding behavior, but also their lattice defect density, which affects the efficiency of ultraviolet emission. The optimal synthesis conditions led to low-tempera

Abstract The formation of circumstellar disks is investigated using three-dimensional resistive magnetohydrodynamic simulations in which the initial prestellar cloud has a misaligned rotation axis with respect to the magnetic field. We examine the effects of (i) the initial angle difference between the global magnetic field and the cloud rotation axis ( θ 0 ) and (ii) the ratio of the thermal to gravitational energy ( α 0 ). We study 16 models in total and calculate the cloud evolution until ∼50

Recent observations uncover various phenomena around the protostar such as misalignment between the outflow and magnetic field, precession of the jet, and time variability of the ejected clumps, whose origins are under debate. We perform a three-dimensional resistive magnetohydrodynamics simulation of the protostar formation in a star-forming core whose rotation axis is tilted at an angle 45° with respect to the initial magnetic field, in which the protostar is resolved with a spatial resolution

We investigate the rotation velocity of the first stars by modelling the angular momentum transfer in the primordial accretion disc.Assessing the impact of magnetic braking, we consider the transition in angular momentum transport mode at the Alfv$\acute{\rm e}$n radius, from the dynamically dominated free-fall accretion to the magnetically dominated solid-body one.The accreting protostar at the centre of the primordial star-forming cloud rotates with close to breakup speed in the case without m

We study the thermal evolution of primordial star-forming gas clouds using three-dimensional cosmological simulations. We critically examine how assumptions and approximations made in calculating radiative cooling rates affect the dynamics of the collapsing gas clouds. We consider two important molecular hydrogen cooling processes that operate in a dense primordial gas; H_2 line cooling and continuum cooling by H_2 collision-induced emission. To calculate the optically thick cooling rates, we fo

A phenomenon was discovered that leads to the selective detection of abrupt increases in the temperature of conductive composite thin films consisting of conductive ceramic fillers and an insulating polymer matrix. Examining the heating rate dependence of the positive-temperature–coefficient-of-resistivity (PTCR) effect provided information about this intelligent phenomenon. The anomalous PTCR effect was observed above 0.3 °C min−1 for all the prepared films. However, the magnitude of the anomal

ZnO nanopillar arrays with high aspect ratios, such as the one shown in the figure, are fabricated from aqueous solutions at low temperatures using a polymer mold. The shape and dimensions of the nanopillars can be tuned by appropriately patterning the polymer mold. A hexagonal ZnO nanopillar array shows photonic bandgaps at visible wavelengths, as predicted by photonic band structure calculations.

A wet-chemical deposition method of synthesizing highly oriented, transparent ZnO films on a crystalline template is described. Multi-nucleation and the subsequent growth of ZnO nanodomains at an early stage of wet-chemical deposition leads to the formation of thin hexagonal platelike ZnO crystals spread over the template film. A subsequent temperature increase allows the growth of oriented rods, whose size depends on that of the platelike crystals. Consequently, oriented ZnO films with various

Abstract Recent observations by the James Webb Space Telescope (JWST) discovered unexpectedly abundant luminous galaxies at high redshift, posing possibly a severe challenge to popular galaxy formation models. We study early structure formation in a cosmological model with a blue, tilted power spectrum (BTPS) given by <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>P</mml:mi> <mml:mo stretchy="false">(</mml:mo> <mml:mi>k</mml:mi> <mml:mo stretchy="false">)</mm

Abstract The formation of the first stars in the high-redshift Universe is a sensitive probe of the small-scale, particle physics nature of dark matter (DM). We carry out cosmological simulations of primordial star formation in ultralight, axion-like particle DM cosmology, with masses of 10−22 and 10−21 eV, with de Broglie wavelengths approaching galactic scales (∼ kpc). The onset of star formation is delayed, and shifted to more massive host structures. For the lightest DM particle mass explore

In the ZrO 2 ‐Cr 2 O 3 system, metastable t ‐ZrO 2 solid solutions containing up to 11 mol% Cr 2 O 3 crystallize at low temperatures from amorphous materials prepared by the hydrazine method. The lattice parameter c decreases linearly from 0.5149 to 0.5077 nm with increased Cr 2 O 3 content, whereas the lattice parameter a is a constant value ( a = 0.5077 nm) regardless of the starting composition. At higher temperatures, transformation (decomposition) of the solid solutions proceeds in the foll