The hazard posed by volcanic ballistic projectiles (VBPs) is commonly assessed using trajectory models that estimate impact locations and energies. Recent models simulate the one-way coupling between the erupting gas–ash mixture and particles by inserting the numerically obtained flow field into the equation of particle motion. Model testing typically relies on reproducing observed travel distances in the field, but this approach is hindered by poorly constrained pre-eruptive conditions such as vent overpressure. To overcome this limitation, this study applies a trajectory model based on the steady-state supersonic jet flow field to reproduce experimental trajectory data obtained from high-speed shadowgraph imaging of spherical glass beads initially at rest and accelerated by supersonic jets from an open-ended shock tube. The model successfully reproduces the observed velocity profiles, demonstrating the viability of the one-way coupling approach for dilute particle populations accelerated by supersonic jets. The reproduced trajectories yield particle Reynolds numbers between 103 and 2 × 105. In this range, drag coefficients for both spherical and irregular-shaped particles are largely independent of particle Reynolds number and depend primarily on particle Mach number. Furthermore, an equation for the duration of steady-state supersonic flow conditions is derived, validated, and then used. The equation shows that, in many explosive eruptions, VBPs are predominantly accelerated during the period in which the supersonic jet can be approximated as steady-state. Particle acceleration is strongest near the vent and decreases rapidly with distance, implying that early jet collapse has little influence on maximum VBP velocities.
Amorphous alumina (Al2O3) is an essential oxide material with widespread applications in electronics, catalysis, and coatings, where its properties are critically influenced by structural disorder and defects. Unlike crystalline phases, amorphous alumina cannot be formed by melt-quenching but can be synthesized through other nonmelting routes, often yielding a high fraction of AlO5 units that determine its functionality. In this study, we systematically examined how heating conditions, post-treatment atmospheres, and storage history affect defect formation and optical responses in amorphous alumina. XRD confirmed that all samples remained amorphous after heating or post-treatment. ESR and UV-Vis analyses revealed that heating at 600-800 degrees C generated unidentified ESR signals near g = 1.97, whereas rapid heating and quenching induced g = 2.003 signals associated with oxygen-defect-related paramagnetic centers that correlated with reduced reflectance and gray coloration. Prolonged precursor storage further enhanced these signals, highlighting the sensitivity of defect states to sample history. Post-treatments produced atmosphere-dependent defects: air and oxygen generated some unidentified ESR signals, affecting UV-visible reflectance, while ozone generated unusually strong ESR peaks at g = 2.01-2.02, resembling O-3 and Al-O radicals, which remained stable for months but primarily influenced UV absorption. Long-term storage of amorphous alumina led to the appearance of weak ESR signals and gradual increases in high-g-value signals, although reflectance remained nearly constant. Absorption spectra showed distinct peaks between 3-5 eV depending on the defect species and treatment atmosphere, emphasizing the strong coupling between defect chemistry and optical behavior. Overall, these findings demonstrate that the defect states of amorphous alumina are not fixed by intrinsic local structure alone but are governed by thermal history, treatment atmosphere, and storage conditions. The observed correlations between ESR signals and optical spectra provide fundamental insights into the defect chemistry of amorphous alumina, offering guidelines for tailoring its properties in optical, dielectric, and catalytic applications.
A (0001) alpha-Ga2O3 film was grown by the mist chemical vapor deposition method on a (0001) alpha-Cr2O3 template (100 mu m thick alpha-Cr2O3 layer formed on an alpha-Al2O3 substrate). Benefiting from the small a-axis lattice mismatch between alpha-Ga2O3 and alpha-Cr2O3, a high-quality alpha-Ga2O3 film with a small twist distribution, and consequently a low edge dislocation density, was coherently grown on an alpha-Cr2O3 template. The edge dislocation density of 7 & times; 10(7) cm(-2), estimated from the full-width at half-maximum value of the X-ray rocking curve (XRC) in X-ray diffraction (XRD), was more than two orders of magnitude lower than that of the film grown on an alpha-Al2O3 substrate, and was almost consistent with that of the alpha-Cr2O3 template. The bright-field transmission electron microscopy (TEM) image supports the dislocation density estimated from the XRD measurements. The high-angle annular dark-field scanning TEM and inverse fast Fourier transform images indicate coherent growth, with almost no misfit dislocations generated at the alpha-Ga2O3/alpha-Cr2O3 interface.
Functional ceramics are playing an increasingly important role in addressing the climate crisis by significantly reducing greenhouse gas emissions. These highly engineered materials enable a wide range of cutting-edge applications due to their multifunctional properties and are recognized as a critical class of materials. In this commentary, we highlight the historical perspective, recent trends, and current status of selected functional ceramics—such as glass-ceramics and high-temperature superconducting ceramics—along with their potential to accelerate the transition to a low-carbon future. In the context of practical energy technologies, ion conducting glass-ceramics can exhibit an electrical conductivity of 10-5 10-3 S·cm-1 at room temperature, which facilitates efficient ion transport and enhances their performance in energy storage systems. High-temperature superconducting ceramics, particularly second-generation REBa2Cu3Oy (RE: Y, Gd, Sm etc.,) coated conductors, can achieve critical current densities on the order of 10⁵–10⁶ A·cm⁻² at the relatively inexpensive liquid-nitrogen temperature of 77.3 K, making them highly promising for efficient power transmission in green energy applications. Emerging applications and their development are also discussed; moreover, this offers a perspective on how these materials can be strategically implemented to maximize their environmental impact.
Physical activity is influenced by built environment, but these associations may differ according to functional capability and subjective and objective environmental measures. Using data from a mail survey of 5,489 community-dwelling older adults, we examined associations between neighborhood environments and physical activity across functional capability levels. Objective environmental factors were associated with physical activity only among the robust group, whereas subjective environmental factors were associated with physical activity across all functional capability groups. These findings suggest that associations between neighborhood environments and physical activity vary by functional capability and highlight importance of policies addressing both subjective and objective environmental factors.
