In high-Reynolds-number turbulence the spatial distribution of velocity fluctuation at small scales is strongly non-uniform. In accordance with the non-uniformity, the distributions of the inertial and viscous forces are also non-uniform. According to direct numerical simulation (DNS) of forced turbulence of an incompressible fluid obeying the Navier–Stokes equation in a periodic box at the Taylor microscale Reynolds number $R_\lambda \approx 1100$, the average $\langle R_{loc}\rangle$ over the space of the ‘local Reynolds number’ $R_ {loc}$, which is defined as the ratio of inertial to viscous forces at each point in the flow, is much smaller than the conventional ‘Reynolds number’ given by $Re \equiv UL/\nu$, where $U$ and $L$ are the characteristic velocity and length of the energy-containing eddies, and $\nu$ is the kinematic viscosity. While both conditional averages of the inertial and viscous forces for a given squared vorticity $\omega ^{2}$ increase with $\omega ^{2}$ at large $\omega ^{2}$, the conditional average of $R_ {loc}$ is almost independent of $\omega ^{2}$. A comparison of the DNS field with a random structureless velocity field suggests that the increase in the conditional average of $R_ {loc}$ with $\omega ^{2}$ at large $\omega ^{2}$ is suppressed by the Navier–Stokes dynamics. Something similar is also true for the conditional averages for a given local energy dissipation rate per unit mass. Certain features of intermittency effects such as that on the $Re$ dependence of $\langle R_{loc}\rangle$ are explained by a multi-fractal model by Dubrulle (J. Fluid Mech., vol. 867, 2019, P1).

We have detected [C I] 3P1–3P0 emissions in the gaseous debris disks of 49 Ceti and β Pictoris with the 10 m telescope of the Atacama Submillimeter Telescope Experiment, which is the first detection of such emissions. The line profiles of [C I] are found to resemble those of CO(J=3–2) observed with the same telescope and the Atacama Large Millimeter/submillimeter Array. This result suggests that atomic carbon (C) coexists with CO in the debris disks, and is likely formed by the photodissociation of CO. Assuming an optically thin [C I] emission with the excitation temperature ranging from 30 to 100 K, the column density of C is evaluated to be (2.2 ± 0.2) × 1017 and (2.5 ± 0.7) × 1016 cm−2 for 49 Ceti and β Pictoris, respectively. The C/CO column density ratio is thus derived to be 54 ± 19 and 69 ± 42 for 49 Ceti and β Pictoris, respectively. These ratios are higher than those of molecular clouds and diffuse clouds by an order of magnitude. The unusually high ratios of C to CO are likely attributed to a lack of H2 molecules needed to reproduce CO molecules efficiently from C. This result implies a small number of H2 molecules in the gas disk; i.e., there is an appreciable contribution of secondary gas from dust grains.

With AKARI, we have performed a systematic study of interstellar dust grains in various environments of galaxies. In many cases, the IR emission of dust is an important tool to trace star-forming activities in galaxies. However it is much more than just star-formation tracers. AKARI has revealed the detailed properties of dust grains in regions not relevant to star formation as well, some of which are found not to follow our old empirical knowledge. Because of its unique capabilities, such as near- and far-IR spectroscopy, and all-sky coverage, AKARI has provided new knowledge on the processing of carbonaceous grains including polycyclic aromatic hydrocarbons. We present the latest results obtained from our AKARI observations of the ISM in our Galaxy and nearby galaxies.

We developed ultra-violet field-emission devices using rare-earth nitrides of Al1-xGdxN grown by a reactive radio-frequency magnetron sputtering technique. The Al1-xGdxN phosphor film excited by high-energy electrons shows a resolution limited, narrow intra-orbital luminescence from Gd3+ ions at 318 nm. The devise characteristics depend on injected current and acceleration voltage, which were analyzed by considering multiple excitation process of injected high-energy electrons.

Osteocytes are surrounded by hard bone matrix, and it has not been possible previously to directly observe the in situ architecture of osteocyte morphology in bone. Electron microscope tomography, however, is a technique that has the unique potential to provide three-dimensional (3D) visualization of cellular ultrastructure. This approach is based on reconstruction of 3D volumes from a tilt series of electron micrographs of cells, and resolution at the nanometer level has been achieved. We applied electron microscope tomography to thick sections of silver-stained osteocytes in bone using a Hitachi H-3000 ultra-high voltage electron microscope equipped with a 360° tilt specimen holder, at an accelerating voltage of 2 MeV. Osteocytes with numerous processes and branches were clearly seen in the serial tilt series acquired from 3-μm-thick sections. Reconstruction of young osteocytes showed the 3D topographic morphology of the cell body and processes at high resolution. This morphological data on osteocytes should provide useful information to those who study osteocyte physiology and the several models used to explain their mechanosensory properties.

The molecular composite composed of polyethylene (PE) and poly(vinyl acetate) (PVAc) prepared using supercritical carbon dioxide (scCO2) and its surface modification for biocompatible surface demonstrated the creation of novel polymer biomaterials. In this study, this modification process was applied to the PE narrow tube (inside diameter: 300μm, outside diameter: 600μm, length: 5m). It was confirmed that PVAc was uniformly generated in PE tube by infrared imaging measurement of cross-section. After the acetyl group on the surface was hydrolyzed, phospholipid polymer was immobilized to the hydroxyl group on the surface of the tube. The phospholipid polymer immobilized surface showed a drastic reduction in protein adsorption. The surface of the minute and slender tube can be effectively modified using the feature of carbon dioxide whose surface tension is near zero. The modification technology by scCO2 is a promising for creation of variously-shaped new biomaterials.

The evolution of a small but finite three-dimensional disturbance on a flat uniform vortex sheet is analysed on the basis of a Lagrangian representation of the motion. The sheet at time t is expanded in a double periodic Fourier series: R(λ1, λ2, t) = (λ1, λ2, 0) + Σn,mAn,m exp[i(nλ1 + δmλ2)], where λ1 and λ2 are Lagrangian parameters in the streamwise and spanwise directions, respectively, and δ is the aspect ratio of the periodic domain of the disturbance. By generalizing Moore's analysis for two-dimensional motion to three dimensions, we derive evolution equations for the Fourier coefficients An,m. The behaviour of An,m is investigated by both numerical integration of a set of truncated equations and a leading-order asymptotic analysis valid at large t. Both the numerical integration and the asymptotic analysis show that a singularity appears at a finite time tc = O(lnε−1) where ε is the amplitude of the initial disturbance. The singularity is such that An,0 = O(tc−1) behaves like n−5/2, while An,±1 = O(εtc) behaves like n−3/2 for large n. The evolution of A0,m(spanwise mode) is also studied by an asymptotic analysis valid at large t. The analysis shows that a singularity appears at a finite time t = O(ε−1) and the singularity is characterized by A0,2k ∝ k−5/2 for large k.

A class of exact solutions of the Navier–Stokes equations is derived. Each of them represents the velocity field v=U+u of a thin vortical layer (a planar jet) under a uniform strain velocity field U in three-dimensional infinite space, and provides a simple flow model in which nonlinear coupling between small eddies plays a key role in small-scale vortex dynamics. The small-scale structure of the velocity field is studied by numerically analysing the Fourier spectrum of u. It is shown that the Fourier spectrum of u falls off exponentially with wavenumber k for large k. The Taylor expansion in powers of the coordinate (say y) in the direction perpendicular to the vortical layer suggests that the solution may be well approximated by a function with certain poles in the complex y-plane. The Fourier spectrum based on the singularities is in good agreement with that obtained numerically, where the exponential decay rate is given by the distance of the poles from the real axis of y.