Fish fauna off sandy beaches, in an estuary, and in a seagrass bed in Hiroshima Bay, Seto Inland Sea

From February 2015 to January 2016, we collected fish monthly using a beach seine net at two sandy beaches (B1 and B2), in a muddy sand estuary (MS), and in a seagrass bed (SG) in Hiroshima Bay, western Japan. A total of 2920 fish in 50 species were collected. The number of species, individuals, and biomass (total weight) were greater at SG and MS than at B1 and B2. The numerically most dominant species were Favonigobius gymnauchen and Tridentiger trigonocephalus at B1 and B2, F. gymnauchen and Acentrogobius sp. 2 at MS, and Plotosus japonicus and Rudarius ercodes at SG. Fish diversity also was higher at MS and SG than at B1 and B2 throughout the year. Fish assemblages and their patterns varied between sites, indicating that each habitat plays an important role as the nursery ground for different fishes

Strange filamentary structures ("fireballs") around a merger galaxy in the Coma cluster of galaxies

We found an unusual complex of narrow blue filaments, bright blue knots, and H-alpha emitting filaments and clouds, which morphologically resembled a complex of ``fireballs,'' extending up to 80 kpc south from an E+A galaxy RB199 in the Coma cluster. The galaxy has a highly disturbed morphology indicative of a galaxy--galaxy merger remnant. The narrow blue filaments extend in straight shapes toward the south from the galaxy, and several bright blue knots are located at the southern ends of the filaments. The Rc band absolute magnitudes, half light radii and estimated masses of the bright knots are -12 - -13 mag, 200 - 300 pc and 10^6-7 Msolar, respectively. Long, narrow H-alpha emitting filaments are connected at the south edge of the knots. The average color of the fireballs is B - Rc = 0.5, which is bluer than RB199 (B - R = 0.99), suggesting that most of the stars in the fireballs were formed within several times 10^8 yr. The narrow blue filaments exhibit almost no H-alpha emission. Strong H-alpha and UV emission appear in the bright knots. These characteristics indicate that star formation recently ceased in the blue filaments and now continues in the bright knots. The gas stripped by some mechanism from the disk of RB199 may be traveling in the intergalactic space, forming stars left along its trajectory. The most plausible fireball formation mechanism is ram pressure stripping by high-speed collision between the galaxy and the hot intra-cluster medium. The fireballs may be a snapshot of diffuse intra-cluster population formation, or halo star population formation in a cluster galaxy.Comment: 13 pages, 14 figures, submitted to Ap

Majorana-fermion origin of the planar thermal Hall effect in the Kitaev magnet α-RuCl₃

磁性絶縁体におけるマヨラナ粒子の決定的証拠 --トポロジカル量子コンピューター実現に向けて前進--. 京都大学プレスリリース. 2024-03-14.The field-induced quantum-disordered state of layered honeycomb magnet α-RuCl₃ is a prime candidate for Kitaev spin liquids hosting Majorana fermions and non-Abelian anyons. Recent observations of anomalous planar thermal Hall effect demonstrate a topological edge mode, but whether it originates from Majorana fermions or bosonic magnons remains controversial. Here, we distinguish these origins from combined low-temperature measurements of high-resolution specific heat and thermal Hall conductivity with rotating magnetic fields within the honeycomb plane. A distinct closure of the low-energy bulk gap is observed for the fields in the Ru-Ru bond direction, and the gap opens rapidly when the field is tilted. Notably, this change occurs concomitantly with the sign reversal of the Hall effect. General discussions of topological bands show that this is the hallmark of an angle rotation–induced topological transition of fermions, providing conclusive evidence for the Majorana-fermion origin of the thermal Hall effect in α-RuCl₃

Feasibility Study of Technology Demonstration Mission for Integrated Attitude-Orbit Control of Solar Sail

We are developing a micro solar sail called PIERIS . The purpose of this project is to demonstrate the following two world-first technologies in Low Earth Orbit. The first technology is to control the external torque with a single gimbal motor. It will be possible to achieve a completely propellant-free Integrated Attitude-Orbit Control. The second technology is a sail structure that guarantees the accuracy of the Pyramid-Shaped sail membrane shape and reduces disturbance torque caused by membrane surface deformation. This project has been selected for the Feasibility-Study phase of the JAXA Small Satellite Rush Program and is scheduled for launch in FY2026 if approved to proceed to the next phase. We are currently conducting mission and system feasibility studies and developing a Bread Board Model

Habitat utilization and secondary production of the sharp-nosed sand goby Favonigobius gymnauchen around intertidal areas

The sharp-nosed sand goby Favonigobius gymnauchen is one of the most dominant fish species around tidal flats and sandy beaches in Japan and plays an important role in the food web. To clarify the habitat utilization and secondary production of F. gymnauchen in these waters, we investigated the density, size compositions, feeding, and prey availability in sandy beaches, a muddy sand estuary, and a seagrass bed in Hiroshima Bay, central Seto Inland Sea, Japan. The density of F. gymnauchen was the highest in the estuarine habitat and the lowest in the sandy beaches. They mainly consumed copepods, gammarids, and polychaetes. The body sizes of F. gymnauchen were larger in the estuarine habitat than in the seagrass bed, although prey availability was higher in the seagrass bed than in the estuary. Secondary production of F. gymnauchen was the highest (> 1 g wet weight m−2 year−1) in the estuarine habitat. The growth rate in the estuarine habitat was estimated to be 0.2 mm d−1. In a laboratory experiment in which fish were exposed to various salinity conditions and fed excess food, the feeding and growth of F. gymnauchen were not significantly different at salinities of 5, 15, and 30, and the maximum growth of juveniles at nearly 25 °C was estimated to be 0.2 mm d−1. These results indicate that F. gymnauchen grows at nearly maximum rates in estuarine habitats despite their high density, thereby resulting in the high secondary production of this species.This study was partly supported by JSPS KAKENHI Grant Number 19K06207

Importance of experienced thermal history: effect of acclimation temperatures on the high-temperature tolerance and growth performance of juvenile marbled flounder

Experienced thermal history often affects the temperature tolerance of fish; however, the effect of thermal history on growth performance is unclear. To contribute to effective stocking (release of hatchery-reared juveniles in the field), we conducted four laboratory experiments using juvenile marbled flounder (Pseudopleuronectes yokohamae, around 30 mm standard length and 0.3 g body wet weight) acclimated at 12 °C and 24 °C for approximately 2 weeks to investigate the effects of acclimation temperature on high-temperature tolerance, food consumption, and growth performance. The acclimation to 24 °C increased tolerance to high temperatures, as shown in a 24-h exposure experiment and in a temperature elevation experiment. The 50% lethal temperature (upper incipient lethal temperature) was estimated to be 25.9 °C and 29.0 °C for the 12 °C and 24 °C acclimation groups, respectively. In subsequent experiments, we tested the effects of high and low temperature acclimation on the food consumption and growth performance of two size groups of juveniles (28.7 ± 2.0 and 34.5 ± 2.9 mm, mean ± SD), that were reared at temperatures ranging from 14 °C to 23 °C. The optimal temperature for growth was 20 °C and did not differ between the acclimation temperatures or between the size groups. However, food consumption and growth performance were suppressed by acute temperature changes. Specifically, feeding and growth were lower in the 24 °C-acclimated group than in the 12 °C-acclimated group when exposed to 14 °C, which is close to the natural water temperature at release in the field. These results suggest that experienced thermal history does not affect the optimal temperature but can affect the growth performance of juveniles. To maximize the post-release growth of hatchery-reared juveniles, the influence of thermal history should be taken into consideration and acute thermal changes before release should be avoided.This study was partly supported by the Ministry of Agriculture, Forestry and Fisheries of Japan and by JSPS KAKENHI Grant Number 19K06207