Three-mode Cepheid pulsation

We simulated two models of classical Cepheids with the same effective temperature and luminosity but different masses. Neither model has significant resonance among linear nonadiabatic periods of the fundamental, the first overtone, and the second overtone radial modes. The higher mass model found to approach to the second overtone-only state. The lower mass model shows a complicated three-mode interaction and none of the amplitudes of three modes is negligible. The relation of the higher mass model to the shortest period Cepheid HR 7308, and that of the lower mass model to the double-mode Cepheids are discussed. It appears that three-mode nonresonant coupling should be considered to explain the behaviours of both models.     

Two stage growth of microdiamond in UHP dolomite marble from Kokchetav Massif, Kazakhstan

The abundance and morphology of microdiamond in dolomite marble from Kumdy‐kol in the Kokchetav Massif, are unusual; a previous study estimated the maximum content of diamonds in dolomite marble to be about 2700 carat ton^?1. Microdiamond is included primarily in garnet, and occasionally in diopside and phlogopite pseudomorphs after garnet. They are classified into three types on the basis of their morphology: (1) S‐type: star‐shaped diamond consisting of translucent cores and transparent subhedral to euhedral very fine‐grained outer parts; (2) R‐type: translucent crystals with rugged surfaces; and (3) T‐type: transparent, very fine‐grained crystals. The S‐type is the most abundant. Micro‐Laue diffraction using a 1.6‐µm X‐ray beam‐size demonstrated that the cores of the star‐shaped microdiamond represent single crystals. In contrast, the most fine‐grained outer parts usually have different orientations compared to the core. Laser–Raman studies indicate that the FWHM (Full Width at Half Maximum) of the Raman band of the core of the S‐type diamond is slightly larger than that for the outer parts. Differences in morphology, crystal orientations, and in the FWHM of the Raman band between the core and the fine‐grained outer‐parts of S‐type microdiamond suggest that the star‐shaped microdiamond was formed discontinuously in two distinct stages.     

Crystallization temperature determination of Itokawa particles by plagioclase thermometry with X‐ray diffraction data obtained by a high‐resolution synchrotron Gandolfi camera

The crystallization temperatures of Itokawa surface particles recovered by the space probe Hayabusa were estimated by a plagioclase geothermometer using sodic plagioclase triclinicity. The Δ131‐index required for the thermometer, which is the difference in X‐ray diffraction peak positions between the 131 and 11 reflections of plagioclase, was obtained by a high‐resolution synchrotron Gandolfi camera developed for the third generation synchrotron radiation beamline, BL15XU at SPring‐8. Crystallization temperatures were successfully determined from the Δ131‐indices for four particles. The observed plagioclase crystallization temperatures were in a range from 655 to 660 °C. The temperatures indicate crystallization temperatures of plagioclases in the process of prograde metamorphism before the peak metamorphic stage.     

When did cosmic acceleration start? How fast was the transition?

Cosmic acceleration is investigated through a kink-like expression for the deceleration parameter (q). The new parametrization depends on the initial (q_i) and final (q_f) values of q, on the redshift of the transition from deceleration to acceleration (z_t) and the width of such transition (τ). We show that although supernovae (SN) observations (Gold182 and SNLS data samples) indicate, at high confidence, that a transition occurred in the past (z_t > 0) they do not, by themselves, impose strong constraints on the maximum value of z_t. However, when we combine SN with the measurements of the ratio between the comoving distance to the last scattering surface and the SDSS + 2dfGRS BAO distance scale (S_k/D_v) we obtain, at 95.4% confidence level, and for (S_k/D_v+Gold182), and and for (S_k/D_v+SNLS), assuming q_i = 0.5 and q_f = −1. We also analyze the general case, q_f  (−∞, 0) finding the constraints that the combined tests (S_k/D_v+SNLS) impose on the present value of the deceleration parameter (q₀).     

Paleomagnetic stratigraphy and biostratigraphy of the Plio-Pleistocene in the Kinki district, Japan

The magnetostratigraphic subdivision of the Plio-Pleistocene series in the Kinki district around Osaka in southwest Japan, based on NRM measurements of volcanic ash beds, is correlated with biostratigraphic and paleoclimatic marker beds as well as past sea level oscillations. At least 10 high sea level stands occurred in the study area between about 1.5 and 0.27 million years ago, all associated with relative warming. A significant change in the composition of flora, from Metasequoia to Fagus dominated assemblages, was observed around the Jaramillo event.     

X-ray beaming caused by resonance scattering in the accretion column of magnetic cataclysmic variables

Extremely strong ionized Fe emission lines, with equivalent widths reaching ∼4000 eV, were discovered by ASCA from a few Galactic compact objects, including AX J2315−0592, RX J1802.1+1804 and AX J1842.8−0423. These objects are thought to be binary systems containing magnetized white dwarfs (WDs). A possible interpretation of the strong Fe K line is the line-photon collimation in the WD accretion column, as a result of resonance scattering of line photons. The collimation occurs when the accretion column has a flat shape, and the effect is augmented by the vertical velocity gradient, which reduces the resonant trapping of resonant photons along the magnetic field lines. This effect was quantitatively confirmed with Monte Carlo simulations. Furthermore, with ASCA observations of the polar V834 Centauri, this collimation effect was clearly detected as a rotational modulation of the equivalent width of the Fe K emission line. The extremely strong emission lines mentioned above can be explained consistently by our interpretation. Combining this effect with other X-ray information, the geometry and plasma parameters in the accretion column were determined.     

Western Arctic primary productivity regulated by shelf-break warm eddies

The response of phytoplankton to the Beaufort shelf-break eddies in the western Arctic Ocean is examined using the eddy-resolving coupled sea ice–ocean model including a lower-trophic marine ecosystem formulation. The regional model driven by the reanalysis 2003 atmospheric forcing from March to November captures the major spatial and temporal features of phytoplankton bloom following summertime sea ice retreat in the shallow Chukchi shelf and Barrow Canyon. The shelf-break warm eddies spawned north of the Barrow Canyon initially transport the Chukchi shelf water with high primary productivity toward the Canada Basin interior. In the eddy-developing period, the anti-cyclonic rotational flow along the outer edge of each eddy moving offshore occasionally traps the shelf water. The primary production inside the warm eddies is maintained by internal dynamics in the eddy-maturity period. In particular, the surface central area of an anti-cyclonic eddy acquires adequate light, nutrient, and warm environment for photosynthetic activity partly attributed to turbulent mixing with underlying nutrient-rich water. The simulated biogeochemical properties with the dominance of small-size phytoplankton inside the warm eddies are consistent with the observational findings in the western Arctic Ocean. It is also suggested that the light limitation before autumn sea ice freezing shuts down the primary production in the shelf-break eddies in spite of nutrient recovery. These results indicate that the time lag between the phytoplankton bloom in the shelf region following the summertime sea ice retreat and the eddy generation along the Beaufort shelf break is an important index to determine biological regimes in the Canada Basin.     

Overview of the MITI Nankai Trough Wells: A Milestone in the Evaluation of Methane Hydrate Resources

Abstract. Bottom-simulating reflectors suggestive of the presence of methane hydrates are widely distributed below the ocean floor around Japan. In late 1999, drilling of the MITI Nankai Trough wells was conducted to explore this potential methane hydrate resource and a Tertiary conventional structure. The wells are located in the Northwest Pacific Ocean off Central Japan at a water depth of 945 m. A total of six wells were drilled, including the main well, two pilot wells, and three post survey wells at intervals of 10–100 m. All wells except the first confirmed the occurrence of hydrates based on logging-while-drilling, wire-line logging and/or coring using a pressure and temperature coring system in addition to conventional methods. Based on the various well profiles, four methane hydrate-bearing sand-rich intervals in turbidite fan deposits were recognized. Methane hydrates fill the pore spaces in these deposits, reaching saturation of up to 80 % in some layers. The methane hydrate-bearing turbiditic sand layers are less than 1 m thick, with a total thickness of 12–14 m. The bottom depth of high hydrate concentration correlates well with the depth of the bottom-simulating reflector. Based on these exploration results, the Japanese government inaugurated a 16-year methane hydrate exploitation program in 2001.     

IPS observations at stelab for the fruitful coming decade

We have been carrying out solar wind measurements using the interplanetary scintillation (IPS) method. Our IPS observation system is operated at a frequency of 327MHz and consists of four stations located at Toyokawa, Fuji, Sugadaira and Kiso. The present system, however, has insufficient sensitivity to measure enough IPS sources for observing the solar wind with adequate spatial and temporal resolution. Therefore we have been excuting the upgrade project since 1994 in order to observe a larger number of compact radio sources. The Fuji system has been improved successfully and has achieved sensitivity by a factor over five compared with the previous system. The upgrade project is now in progress for the Toyokawa and Sugadaira station.     

Three-mode Cepheid pulsation

Amplitude equations, that are used in the investigation of stellar pulsations, for the three-mode nonresonant coupling case are inferred from that of the two-mode nonresonant coupling case. Characteristics of the fixed points of the amplitude equations are studied. Chaotic behaviour is expected when the amplitude equations consist of more than two modes.