Disk illumination by black hole superradiance of electromagnetic perturbations

Using the Kerr-Schild formalism to solve the Einstein-Maxwell equations, we study energy transport due to time-dependent electromagnetic perturbations around a Kerr black hole, which may work as a mechanism to illuminate a disk located on the equatorial plane. For such a disk-hole system it is found that the energy extraction from the hole can occur under the well-known superradiance condition for wave frequency, even though the energy absorption into the hole should be rather dominant near the polar region of the horizon. We estimate the efficiency of the superradiant amplification of the disk illumination. Further we calculate the time-averaged energy density distribution to show explicitly the existence of a negative energy region near the horizon and to discuss the possible generation of a hot spot on the disk.Comment: 11 pages, 4 figures, corrected typos, published in Physical Review

台風201326号出水に伴う新田川起源懸濁態放射性核種の沿岸域でのインベントリ解析

福島新田川流域には原発事故直後に大量の放射性セシウム137が大気経由で沈着し，河道に集積した高濃度の懸濁態137Csが出水毎に間欠的に海域へ供給され，沿岸域の底質環境に影響を与え続けている．本研究では，4段ネストJCOPE2-ROMS海洋モデル，多粒径3次元土砂輸送モデル，波浪推算モデルSWAN，河道モデルiRIC-Nays2DH，放射性核種吸着モデルを連成させた超高解像度広域土砂・懸濁態137Cs海洋分散モデリングを行い，台風201326号出水イベントに伴う河川起源土砂の河口・沿岸域における堆積・浸食状況の時空間特性を評価した．さらに懸濁態137Csインベントリ解析を行い，水深5 mまでの河口域，水深10mまでの河口外縁域での堆積，沿岸漂砂等による河川起源137Csの海域堆積層への移行特性を定量化した

A storm-induced flood and associated nearshore dispersal of the river-derived suspended 137Cs

Accidental leakage of radionuclides from the Fukushima Nuclear Power Plant (FNPP1) took place in the aftermath of the catastrophic tsunamis associated with the Great East Japan Earthquake that occurred on March 11, 2011. Significant amount of radionuclides released into the atmosphere were reportedly transported and deposited on land located near FNPP1. The Niida River, Fukushima, Japan, has been recognized as a terrestrial source of highly contaminated suspended radiocesium adhering to sediment particles in the ocean through the river mouth as a result of hydrological processes.Particularly, we investigated the storm and subsequent floods associated with Typhoon 201326 (Wipha) that passed off the Fukushima coast in October 2013, and subsequently promoted precipitation to a considerable extent and associated riverine freshwater discharge along with sediment outfluxes to the ocean. Using in situ bed sediment core data obtained from regions near the river mouth, we conducted a quantitative assessment of the accumulation and erosion of the sediments and explored the resultant suspended radiocesium distribution around the river mouth and nearshore areas along the Fukushima coast. We identified three major accumulative areas, near the river mouth within an area < 1 km, around the breakwaters in the north of the river mouth, and along the southern coastal area, while offshore and northward transports were minor. The present study clearly exhibits substantial retention of the land-derived radiocesium adhered to the sediments in the coastal areas, leading to possible long-term influences on the surrounding marine environment