Heat extraction through a geothermal reservoir on an oblique fault plane

The heat extraction through a geothermal reservoir on an oblique fault plane in the earth's crust is considered. The fault could be modelled mechanically as a frictional contact interface of two elastic bodies. The heat is recovered by circulating fluid through the reservoir, and then the surface of the reservoir is cooled by the fluid. The analysis is based on the two-dimensional theory of quasi-static thermoelasticity. It is concluded from numerical calculations that a geothermal reservoir can be created on an oblique fault plane, and the opened region, i.e. the fluid-filled region, increases gradually with time during the heat extraction. Also discussed are the effects of the fluid pressure and the coefficient of friction on the behaviour of the reservoir.     

Star formation induced by supersonic turbulence in interstellar molecular cloud

We studied fragmentation process of the interstellar molecular cloud which is predominated by supersonic turbulence with special regard to collisions of turbulent gas elements and formation of a shock-compressed layer by receding shock waves. The propagation of the shock waves and the evolution of the compressed layer are followed by one-dimensional gas dynamical simulation until self-gravity becomes significant, taking account of the effects of thermal properties of the molecular gas and magnetic fields. It is shown that the efficient cooling by CO molecules and its sensitive dependence on gas density make the shock-compressed layer so cold and dense that the layer becomes gravitationally unstable and breaks into fragments even if the gas elements are gravitationally stable prior to the collision. The mass of the unstable fragment is estimated to be about two solar masses or less, irrespective of the presence of the magnetic field. The stars formed by collisions of supersonic turbulent gas elements accelerate the surrounding gas in T Tauri stage and replenish the turbulent energy to maintain the mechanical equilibrium of the molecular cloud.     

AMS 14C ages and petrological features for solidified fractures with carbonates at coastal outcrops of Yakushima Island, Japan

This paper describes the petrological features and the ages of rock fractures filled mainly with carbonates at coastal outcrops of Yakushima Island, Japan. Microscopic observation and geochemical analysis were used to investigate the petrological features and the compositions of the fracture fillings. In addition, AMS ¹⁴C dating was also performed to estimate the ages of them. Microscopic study indicated that the fracture fillings contain not only cementing materials but also lithic fragments from host rock and bioclasts. SEM observation showed that the cements exhibit the characteristic textures of beachrocks. The cements were identified as Mg-calcite from XRD analysis. It was also observed from geochemical analysis that there were at least two stages of precipitation within the fractures. In addition, AMS ¹⁴C dating for seventeen samples of fracture fillings showed that the ages range from 2,460 to 5,130 years BP which is found to be younger than that of the uplifted coral at Yakushima Island (approximately 5,300–5,600 years BP). The results suggest that the fractures were solidified after the coral was uplifted.     

Phase relations in the carbon-saturated C–Mg–Fe–Si–O system and C and Si solubility in liquid Fe at high pressure and temperature: implications for planetary interiors

The phase and melting relations of the C-saturated C–Mg–Fe–Si–O system were investigated at high pressure and temperature to understand the role of carbon in the structure of the Earth, terrestrial planets, and carbon-enriched extraterrestrial planets. The phase relations were studied using two types of experiments at 4 GPa: analyses of recovered samples and in situ X-ray diffractions. Our experiments revealed that the composition of metallic iron melts changes from a C-rich composition with up to about 5 wt.% C under oxidizing conditions (ΔIW = ?1.7 to ?1.2, where ΔIW is the deviation of the oxygen fugacity (fO₂) from an iron-wüstite (IW) buffer) to a C-depleted composition with 21 wt.% Si under reducing conditions (ΔIW < ?3.3) at 4 GPa and 1,873 K. SiC grains also coexisted with the Fe–Si melt under the most reducing conditions. The solubility of C in liquid Fe increased with increasing fO₂, whereas the solubility of Si decreased with increasing fO₂. The carbon-bearing phases were graphite, Fe₃C, SiC, and Fe alloy melt (Fe–C or Fe–Si–C melts) under the redox conditions applied at 4 GPa, but carbonate was not observed under our experimental conditions. The phase relations observed in this study can be applicable to the Earth and other planets. In hypothetical reducing carbon planets (ΔIW < ?6.2), graphite/diamond and/or SiC exist in the mantle, whereas the core would be an Fe–Si alloy containing very small amount of C even in the carbon-enriched planets. The mutually exclusive nature of C and Si may be important also for considering the light elements of the Earth’s core.     

Anomalous deformation of the Earth's bow shock in the lunar wake: Joint measurement by Chang’E-1 and SELENE

Because the solar wind (SW) flow is usually super-sonic, a fast-mode bow shock (BS) is formed in front of the Earth's magnetosphere, and the Moon crosses the BS at both dusk and dawn flanks. On the other hand, behind of the Moon along the SW flow forms a tenuous region called lunar wake, where the flow can be sub-Alfvénic (and thus sub-sonic) because of its low-density status. Here we report, with joint measurement by Chang’E-1 and SELENE, that the Earth's BS surface is drastically deformed in the lunar wake. Despite the quasi-perpendicular shock configuration encountered at dusk flank under the Parker-spiral magnetic field, no clear shock surface can be found in the lunar wake, while instead gradual transition of the magnetic field from the upstream to downstream value was observed for a several-minute interval. This finding suggests that the ‘magnetic ramp’ is highly broadened in the wake where a fast-mode shock is no longer maintained due to the highly reduced density. On the other hand, observations at the 100 km altitude on the dayside show that the fast-mode shock is maintained even when the width of the downstream region is smaller than a typical scale length of a perpendicular shock. Our results suggest that the Moon is not so large to eliminate the BS at 100 km altitude on the dayside, while the magnetic field associated with the shock structure is drastically affected in the lunar wake.     

Application of chemical tracers to an estimate of benthic denitrification in the Okhotsk Sea

To estimate benthic denitrification in a marginal sea, we assessed the usefulness of \({\text{N}}_{2}^{*}\) , a new tracer to measure the excess nitrogen gas (N₂) using dissolved N₂ and argon (Ar) with N* in the intermediate layer (26.6–27.4σ _θ ) of the Okhotsk Sea. The examined parameters capable of affecting \({\text{N}}_{2}^{*}\) are denitrification, air injection and rapid cooling. We investigated the relative proportions of these effects on \({\text{N}}_{2}^{*}\) using multiple linear regression analysis. The best model included two examined parameters of denitrification and air injection based on the Akaike information criterion as a measure of the model fit to data. More than 80 % of \({\text{N}}_{2}^{*}\) was derived from the denitrification, followed by air injection. Denitrification over the Okhotsk Sea shelf region was estimated to be 5.6 ± 2.4 μmol kg^?1. The distribution of \({\text{N}}_{2}^{*}\) was correlated with potential temperature (θ) between 26.6 and 27.4σ _θ (r = ?0.55). Therefore, we concluded that \({\text{N}}_{2}^{*}\) and N* can act complementarily as a quasi-conservative tracer of benthic denitrification in the Okhotsk Sea. Our findings suggest that \({\text{N}}_{2}^{*}\) in combination with N* is a useful chemical tracer to estimate benthic denitrification in a marginal sea.     

Long-term (36-year) observations on the dynamics of the fish-killing raphidophyte Chattonella in Harima-Nada,eastern Seto Inland Sea,Japan

Long-term changes of the fish-killing raphidophyte Chattonella spp. (Chattonella antiqua, Chattonella marina and Chattonella ovata) were examined in relation to environmental factors at 19 sampling stations in Harima-Nada, eastern Seto Inland Sea, Japan, for 36 years from 1973 to 2008. Long-term trends in the dynamics of Chattonella populations were considered to relate to environmental factors such as nutrient concentrations and water temperature. High nutrient levels during the period from the 1970s to the early 1980s have contributed to the high cell density and large-scale red tides of Chattonella spp. in Harima-Nada. However, nutrient levels exhibited a decreasing trend thereafter, and it is thought that Chattonella spp. cannot form large-scale blooms under the present conditions. After the mid-1990s, the occurrence period of vegetative cells of Chattonella spp. has been several weeks or 1 month earlier than that of the 1970s and early 1980s, and the appearance frequency of Chattonella spp. has increased in the northern coastal area, although the cell density and the spatial scale of the distribution have become lower and smaller than those in the previous decades. It is suggested that the timing of germination of Chattonella cysts has become earlier as a result of the increase in water temperature, and the chances of vegetative growth have also increased, especially at the northern coast where most of large rivers discharge into the Harima-Nada. In addition, the present results revealed that fewer diatoms were also one of the significant factors for the high abundance of Chattonella spp. in Harima-Nada.     

Characteristics of planetary-scale waves simulated by a new venusian mesosphere and thermosphere general circulation model

We have developed a new general circulation model (GCM) for the venusian mesosphere and thermosphere (80-about 180 km). Our GCM simulations show that winds in the subsolar-to-antisolar direction (SS–AS) are predominant above about 90 km. A weak return flow of the SS–AS is seen below about 90 km. We performed GCM simulations imposing the planetary-scale waves (thermal tides, Rossby wave, and Kelvin wave) at the lower boundary. Although the diurnal and semidiurnal tides are damped below 95 km, the Rossby wave propagates up to around 130 km. However, the amplitude of the Rossby wave is too small (<1 m/s) to affect the general circulation. On the other hand, the Kelvin wave propagates up to about 130 km with a maximum zonal wind fluctuation of approximately 5.9 m/s on average. The amplitude of the Kelvin wave sometimes exceeds 10 m/s around the terminator. The Kelvin wave causes a temporal variation in the wind velocity at the altitude of the O₂-1.27 μm nightglow emission (about 95 km). Using a newly developed 1-D nightglow model and the composition distribution calculated from our GCM, we investigated the impact of the Kelvin wave on the nightglow distribution. Our results suggest that the Kelvin wave would cause temporal variations in the nightglow emission in the 23:50–00:20 LT region with an intensity of 1.1–1.3 MR and a period of approximately 4 days.     

A DUAL mission for nuclear astrophysics

DUAL will study the origin and evolution of the elements and explores new frontiers of physics: extreme energies that drive powerful stellar explosions and accelerate particles to macroscopic energies; extreme densities that modify the laws of physics around the most compact objects known; and extreme fields that influence matter in a way that is unknown on Earth. The variability of these extreme objects requires continuous all-sky coverage, while detailed study demands an improvement in sensitivity over previous technologies by at least an order of magnitude. The DUAL payload is composed of an All-Sky Compton Imager (ASCI), and two optical modules, the Laue-Lens Optic (LLO) and the Coded-Mask Optic (CMO). The ASCI serves dual roles simultaneously, both as an optimal focal-plane sensor for deep observations with the optical modules and as a sensitive true all-sky telescope in its own right for all-sky surveys and monitoring. While the optical modules are located on the main satellite, the All-Sky Compton Imager is situated on a deployable structure at a distance of 30?m from the satellite. This configuration not only permits to maintain the less massive payload at the focal distance, it also greatly reduces the spacecraft-induced detector background, and, above all it provides ASCI with a continuous all-sky exposure.