800-km long N-S spreading system of the North Fiji Basin

International audienc

Development of highly radiopure NaI(Tl) scintillator for PICOLON dark matter search project

Highly radiopure NaI(Tl) was developed to search for particle candidates of dark matter. Optimized methods were combined to reduce various radioactive impurities. 40K was effectively reduced by the recrystallization method. The progenies of the decay chains of uranium and thorium were reduced by appropriate resins. The concentration of natural potassium in NaI(Tl) crystal was reduced to 20 ppb. Concentrations of alpha-ray emitters were successfully reduced by appropriate resin selection. The present concentrations of the thorium series and 226Ra were 1.2±1.4μBq/kg and 13±4μBq/kg, respectively. No significant excess in the concentration of 210Pb was obtained, and the upper limit was 5.7 μBq/kg at 90% CL. The achieved level of radiopurity of NaI(Tl) crystals makes the construction of a dark matter detector possible

Seasonal migration of Cnaphalocrocis medinalis (Lepidoptera: Crambidae) over the Bohai Sea in northern China

The rice leaf roller, Cnaphalocrocis medinalis (Guenée), is a serious insect pest of rice with a strong migratory ability. Previous studies on the migration of C. medinalis were mostly carried out in tropical or subtropical regions, however, and what the pattern of seasonal movements this species exhibits in temperate regions (i.e. Northern China, where they cannot overwinter) remains unknown. Here we present data from an 11-year study of this species made by searchlight trapping on Beihuang Island (BH, 38°24′N; 120°55′E) in the centre of the Bohai Strait, which provides direct evidence that C. medinalis regularly migrates across this sea into northeastern agricultural region of China, and to take advantage of the abundant food resources there during the summer season. There was considerable seasonal variation in number of C. medinalis trapped on BH, and the migration period during 2003–2013 ranged from 72 to 122 days. Some females trapped in June and July showed a relatively higher proportion of mated and a degree of ovarian development suggesting that the migration of this species is not completely bound by the ‘oogenesis-flight syndrome’. These findings revealed a new route for C. medinalis movements to and from Northeastern China, which will help us develop more effective management strategies against this pest

High-resolution bathymetry using Alvin scanning sonar at the Southern East Pacific Rise and its implication to the formation of collapsed lava lakes

International audienceA high-resolution bathymetric map of a collapsed lava lake on the ridge crest of the superfast-spreading Southern East Pacific Rise was constructed. The data were acquired during the MOAI'98 Cruise using a pencil-beam scanning sonar that was installed on the submersible Alvin. The map covers an area of 200 × 350 m at the Oasis hydrothermal site (17°25.4'S, 113°12.3'W) where low-temperature fluids are venting from a collapsed lava lake. The collapsed lava lake is 250 m long, with a mean width of 10 m in parallel to the spreading axis on the western flank of the ridge crest. The estimated volume of lava that has drained out is about 7000 m3 erupted from a single event. This small amount of melt and frequent contacts between "young" and "younger" flows indicate that volcanism at the superfast-spreading ridge system is characterized by frequent eruptions of very small volumes of magma