Microfractures occurring in a rock sample that are called acoustic emission (AE) events show some similar features to earthquakes. However, it remains to be shown whether or not AE equate to ultramicroearthquakes. In this study, we show the existence of magnitude À7 level earthquakes based on seismological analyses of AE source parameters. Advances in multichannel, broadband, high-speed continuous recording of AE under seismogenic pressure conditions has facilitated increasingly robust measurement. Source parameters of AE show that AE events satisfy the same scaling relationship as natural earthquakes in which seismic moment is inversely proportional to the cube of corner frequency. This result suggests that both millimeter scale fractures and natural earthquakes of kilometer scale ruptures are highly similar as physical processes. Hence, AE events can be interpreted as ultramicroearthquakes having a magnitude of about À7. These results demonstrate that laboratory observation is an effective approach in studying natural earthquake generation process.
We study the spatial structure of four valence neutrons in the ground state of 8 He and 18 C nuclei using a core+4n model. For this purpose, we employ a density-dependent contact interaction among the valence neutrons, and solve the five-body Hamiltonian in the Hartree-Fock-Bogoliubov (HFB) approximation. We show that two neutrons with the coupled spin of S=0 exhibit a strong dineutron correlation around the surface of these nuclei, whereas the correlation between the two dineutrons is much weaker. Our calculation indicates that the probability of the (1p 3/2 ) 4 and [(1p 3/2 ) 2 (p 1/2 ) 2 ] configurations in the ground state wave function of 8 He nucleus is 34.9% and 23.7%, respectively. This is consistent with the recent experimental finding with the 8 He(p, t) 6 He reaction, that is, the ground state wave function of 8 He deviates significantly from the pure (1p 3/2 ) 4 structure.
The interaction between a columnar vortex and external turbulence is investigated numerically. A Lamb–Oseen vortex is immersed in an initially isotropic homogeneous turbulence field, which itself is produced numerically by a direct numerical simulation of decaying turbulence. The formation of inhomogeneous fine turbulent eddies around the columnar vortex and the vortex-core deformations are studied in detail by visualizing the flow field. The initially random turbulent eddies (worms) are wrapped around the columnar vortex and become spirals. Statistical quantities, such as two-point-energy spectra and two-point-enstrophy spectra, are evaluated and compared with the theoretical predictions from rapid distortion theory. The axial velocity correlation dominates near the vortex surface, whereas the radial velocity correlation becomes larger where the worms are wrapped. Where the columnar vortex is strong compared with the external turbulence, external velocity disturbances are blocked by the vortex and they cannot penetrate into the vortex core directly, whereas various types of vortex waves (Kelvin waves) are excited.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.