Three‐dimensional microstructure of samples recovered from asteroid 25143 Itokawa: Comparison with LL5 and LL6 chondrite particles

In this study, the three‐dimensional (3‐D) microstructure of 48 Itokawa regolith particles was examined by synchrotron microtomography at SPring‐8 during the preliminary examination of Hayabusa samples. Moreover, the 3‐D microstructure of particles collected from two LL6 chondrites (Ensisheim and Kilabo meteorites) and an LL5 chondrite (Tuxtuac meteorite) was investigated by the same method for comparison. The modal abundances of minerals, especially olivine, bulk density, porosity, and grain size are similar in all samples, including voids and cracks. These results show that the Itokawa particles, which are surface materials from the S‐type asteroid Itokawa, are consistent with the LL chondrite materials in terms of not only elemental and isotopic composition of the minerals but also 3‐D microstructure. However, we could not determine whether the Itokawa particles are purely LL5, LL6, or a mixture of the two. No difference between the particles collected from Rooms A and B of the sample chamber, corresponding to the sampling sequence of the spacecraft's second and first touchdowns, respectively, was detected because of the statistically small amount of particles from Room B.     

Criterion for stability of phytoplankton patchiness using a Liapunov method

A criterion for the stability of plankton patchiness is developed using a Liapunov function. Plankton growth, advection and diffusion in a closed area are considered. A critical length scale for the stability does not exist but a more common criterion which contains the growth rateα, diffusion coefficientA _l and arbitrary function of growthf can be introduced in an integral form.     

Sedimentary facies of Maastrichtian to Danian deposits in Amur River area, Russian Far East

Sedimentary facies of the Tsagayan Formation is distributed in the eastern Zeya-Bureya Basin has been analyzed. The formation is of the Maastrichtian to Danian in age and characterized by the cyclicity of the fining-upwards successions. Analysis of environmental changes during the K/T boundary is the focus of this study. Five facies have been identified: Facies A, thick and laterally extensive coarse-grained to medium-gained sandstone units, interpreted as channelfill deposits; Facies B, parallel-laminated to massive mudstone units interpreted as interchannel lakes and flood plain deposits; Facies C, sheet-like medium-grained to fine-grained sandstones interpreted as crevasse splay deposits; Facies D, coal to coaly mudstone beds interpreted as deposits of peatlands; Facies E, very poorly sorted sandy mudstone beds interpreted as debris flow deposits. Fluvial environments with the low-relief fiat topography was inferred. A channel transported large volumes of clasts, and a flood basin with interchannel lakes and peatlands was deciphered. Any distinct change of sedimentary environments has not been identified throughout the Tsagayan Formation (including the K/T boundary). However, two beds of debris flow deposits were identified. The one occurs at the uppermost part of the lower Tsagayan Subformation and contains dinosaur fossils. The other is intercalated in the upper Tsagayan Subformation.     

On the Long-Term Modulation of Solar Differential Rotation

Long-term modulation of solar differential rotation was studied with data from Mt. Wilson and our original observations during Solar Cycles 16 through 23. The results are that i) the global B-value (i.e. latitudinal gradient of differential rotation) is modulated with a period of about six or seven solar cycles, ii) the B-values of the northern and southern hemispheres are also modulated with a period similar to the global one, but iii) they show quasi-oscillatory behavior with a phase shift between them. We examined the yearly fluctuations of the B-values in every solar cycle with reference to the phase of the sunspot cycle and found that the B-values in the sunspot-minimum years show large and erratic variations, while those in the sunspot-maximum years show small fluctuations. Positive correlation between the former B-values and the latter was found. We discuss the independent long-term behavior of solar differential rotation between the northern and southern solar hemispheres and the implication for the solar dynamo.     

The optical reflector system for the CANGAROO-II imaging atmospheric Cherenkov telescope

A new imaging atmospheric Cherenkov telescope with a light-weight reflector has been constructed. Light, robust, and durable mirror facets of containing carbon fiber reinforced plastic laminates were developed for the telescope. The reflector has a parabolic shape (f/1.1) with a 30 m² surface area, which consists of 60 spherical mirror facets. The image size of each mirror facet is 0°.08 (FWHM) on average. The attitude of each facet can be adjusted by stepping motors. After the first in situ adjustment, a point image of about 0°.14 (FWHM) over 3° field of view was obtained. The effect of gravitational load on the optical system was confirmed to be negligible at the focal plane. The telescope has been in operation with an energy threshold for γ-rays of 300 GeV since May 1999.     

Laboratory detection of a new interstellar free radical CH2CN(2B1)

An asymmetric-top free radical CH2CN, which as a 2B1 ground state, was detected for the first time by laboratory microwave spectroscopy. The radical was produced in a free-space absorption cell by a DC glow discharge in pure CH3CN gas. About 60 fine-structure components were observed for the N = 11-10 to 14-13 a-type rotational transitions in the frequency region of 220-260 GHz, and many hyperfine resolved components for the N = 4-3 and 5-4 transitions in the 80 and 100 GHz regions, respectively. The molecular constants, including the rotational constants, centrifugal distortion constants, and spin-rotation coupling constants with centrifugal distortion correction terms were determined from the fine-structure resolved transitions, and the hyperfine coupling constants due to the hydrogen and nitrogen nuclei were obtained from the low-N transitions. As a result we assigned U100602 and U80484 from Sgr B2, and U40240 and U20120 from TMC-1, to the N = 5-4, 4-3, 2-1, and 1-0 transitions with K-1 = 0 of the CH2CN radical.