arXiv subjects

M. Ohkawa

Publications and source records attributed to M. Ohkawa.

4 recordsLinked to original sources

arXiv2024

Evaluation of microseismic motion at the KAGRA site based on ocean wave data

The microseismic motion, ambient ground vibration caused by ocean waves, affects ground-based gravitational wave detectors. In this study, characteristics of the ocean waves including seasonal variations and correlation coefficients were investigated for the significant wave heights at 13 coasts in Japan. The relationship between the ocean waves and the microseismic motion at the KAGRA site was also evaluated. As a result, it almost succeeded in explaining the microseismic motion at the KAGRA site by the principal components of the ocean wave data. One possible application of this study is microseismic forecasting, an example of which is also presented.

physics.ao-ph↗

arXiv2022

Response of the underground environment of the KAGRA observatory against the air-pressure disturbance from the Tonga volcano eruption on January 15th, 2022

On January 15, 2022, at 04:14:45 (UTC), the Hunga Tonga-Funga Ha'apai, a submarine volcano in the Tongan archipelago in the southern Pacific Ocean, erupted and generated global seismic, shock, and electromagnetic waves, which also reached Japan, situated more than 8,000 km away. KAGRA is a gravitational wave telescope located in an underground facility in Kamioka, Japan. It has a wide variety of auxiliary sensors to monitor environmental disturbances which obstruct observation of gravitational waves. The effects of the volcanic eruption were observed by these environmental sensors both inside and outside of the underground facility. In particular, the shock waves made it possible to evaluate the transfer functions from the air pressure wave in the atmosphere to the underground environmental disturbances (air pressure and seismic motion).

astro-ph.IM↗

arXiv2017

The status of KAGRA underground cryogenic gravitational wave telescope

KAGRA is a 3-km interferometric gravitational wave telescope located in the Kamioka mine in Japan. It is the first km-class gravitational wave telescope constructed underground to reduce seismic noise, and the first km-class telescope to use cryogenic cooling of test masses to reduce thermal noise. The construction of the infrastructure to house the interferometer in the tunnel, and the initial phase operation of the interferometer with a simple 3-km Michelson configuration have been completed. The first cryogenic operation is expected in 2018, and the observing runs with a full interferometer are expected in 2020s. The basic interferometer configuration and the current status of KAGRA are described.

gr-qc↗

arXiv2010

Three energy scales characterizing the competing pseudogap state, the incoherent, and the coherent superconducting state in high-Tc cuprates

We have studied the momentum dependence of the energy gap of Bi2(Sr,R)2CuOy by angleresolved photoemission spectroscopy (ARPES), particularly focusing on the difference between R=La and Eu. By comparing the gap function and characteristic temperatures between the two sets of samples, we show that there exist three distinct energy scales, Δpg, Δsc0, and Δeff sc0, which correspond to T* (pseudogap temperature), Tonset (onset temperature of fluctuating superconductivity), and Tc (critical temperature of coherent superconductivity). The results not only support the existence of a pseudogap state below T* that competes with superconductivity but also the duality of competition and superconducting fluctuation at momenta around the antinode below Tonset.

cond-mat.supr-con↗