Stress induced transformation of pigeonites from achondritic meteorites

A transmission electron microscopic (TEM) study was conducted to investigate the stress-induced transformation mechanisms of pigeonites from two achondrites. In pigeonites from the Allan Hills 77257 ureilite, abundant lamellae of orthopyroxene-pigeonite intergrowth accompanied by minor amounts of blebby augite precipitates were observed. In pigeonites from the Juvinas eucrite, some stacking faults running through the (001) augite lamellae were observed although most of the stacking faults terminated at the host-lamella interface. High resolution TEM observation shows the fringe offset produced by the stacking fault in the Juvinas pigeonites. The magnitude of the mismatch parallel to [001] is approximately c/4, which is related to the formation of the partial edge dislocation near the host-lamella interface. The partial dislocation is imaged as an edge dislocation with an (002) extra-plane. Three partial dislocation mechanisms with distinct displacement vectors are proposed in order to explain the stress-induced transformation textures observed in the achondritic pyroxenes. Further study will be required to determine unequivocally the mechanism of atomic displacements during stress-induced transformation. However, regardless of the actual mechanism of transformation, it is not difficult to convert orthopyroxene to clinopyroxene or vice versa by this transformation from the structural point of view. Low-Ca pyroxenes are deformed without a stress-induced transformation by slip at high temperature and geologically reasonable strain rates. However, meteoritic pyroxenes can be deformed by stress-induced transformation even at high temperature because preterrestrial impact processes will produce a deformation condition with high strain rates. Deformation at high strain rates and high temperature is very important when we interpret the microtexture of meteoritic pyroxenes.     

Qualitative correlation of marine mammals with physical and biological parameters in the Ligurian Sea

In support of its acoustic risk mitigation policy, NATO SACLANT Undersea Research Centre (SACLANTCEN) is sponsoring a series of sea trials, entitled "Sirena" to collect a multiyear integrated oceanographic, biological, and hydrographic data set, the goal being to explain, based on these parameters, the distribution of marine mammals found in specific locations. By understanding how ocean dynamics affects the distribution and behavior of whales and the organisms forming the food web upon which the whales feed, it may be possible to conduct acoustic exercises in areas of low cetacean density. The first two Sirena multidisciplinary cruises were conducted in the Ligurian Sea in late summer time frame during 1999 and 2000. The focus of this analysis is to determine whether remotely sensed satellite data can indicate nutrient-rich regions in areas where the oceanography is known and to determine if these regions of higher productivity, coupled with knowledge of cetacean presence from all available sources, could be used as an indicator of marine mammal presence for acoustic risk mitigation purposes. For the two years of data examined, cooler sea-surface temperature data correlated with high levels of chlorophyll production as seen by remotely sensed images. This remotely sensed data correlated well with measured subsurface values of the same parameters. Coincident sightings of three species of marine mammals indicated that fin and sperm whales generally preferred the deep, nutrient-rich portion of the basin while Cuvier's beaked whales preferred a submarine canyon where there is a frontal influence, as indicated from satellite data and historical oceanography. This paper is intended as a contribution to the longer term objective of developing the means to accurately predict cetacean presence from physical oceanographic characteristics.     

On the X-ray image of the Crab nebula: comparison with Chandra observations

An axisymmetric model for the Crab nebula is constructed to examine the flow dynamics in the nebula. The model is based on that of Kennel & Coroniti, although we assume that the kinetic-energy-dominant wind is confined to an equatorial region. The evolution of the distribution function of the electron–positron plasma flowing out in the nebula is calculated. Given viewing angles, we reproduce an image of the nebula and compare it with the Chandra observation.
The reproduced image is not ring-like, but is rather 'lip-shaped'. It is found that the assumption of a toroidal field does not reproduce the Chandra image. We must assume that there is a disordered magnetic field with an amplitude as large as the mean toroidal field. In addition, the brightness contrast between the front and back sides of the ring cannot be reproduced if we assume that the magnetization parameter σ is as small as ∼10⁻³. The brightness profile along the semimajor axis of the torus is also examined. The non-dissipative, ideal-magnetohydrodynamic approximation in the nebula appears to break down.
We speculate that if the magnetic energy is released by some process that produces a turbulent field in the nebula flow and causes heating and acceleration – for example, by magnetic reconnection – then the present difficulties may be resolved (i.e. we can reproduce a ring image and a higher brightness contrast). Thus, the magnetization parameter σ can be larger than previously expected.     

Hydrological control of dissolved organic carbon dynamics in a forested headwater catchment,Kiryu Experimental Watershed,Japan

To evaluate the influence of hydrological processes on dissolved organic carbon (DOC) dynamics in a forested headwater catchment, DOC concentration was observed along the flow path from rainfall to stream water via throughfall, soil water, groundwater, and spring water for 4 years, and DOC flux through the catchment was calculated. The spatial and temporal variations in DOC concentration and flux were compared with physical hydrological observations and the mean residence time of water. In the upslope soil layer, DOC concentrations were not significantly correlated with water fluxes, suggesting that DOC concentrations were not strictly controlled by water fluxes. In the upslope perennial groundwater, DOC concentration was affected by the change in the amount of microbial degradation of DOC produced by changes in the mean residence time of water. In stream water, the temporal variation in DOC concentration was usually affected by changes in DOC concentration of the inflow component via vertical infiltration from above the perennial groundwater. During dry periods, however, the component from inflow via vertical infiltration was negligible and DOC in the upslope perennial groundwater became the major component of stream water DOC. The temporal variation in stream water DOC concentration during baseflow was affected by rainfall patterns over several preceding months. Therefore, records of rainfall over several preceding months are one of the most important factors for predicting changes in DOC concentration on a catchment scale. Copyright © 2007 John Wiley & Sons, Ltd.     

Galactic winds from primeval galaxies

Ultra-high resolution hydrodynamic simulations using 1024³ grid points are performed of early supernova burst in a forming galaxy, with properties similar to those inferred for Lyman α emitters (LAEs) and Lyman Break Galaxies (LBGs). We show that, at the earliest stages of less than 300 Myr, continual supernova explosions produce multitudinous hot bubbles and cooled H(I) shells in-between. The H(I) shells radiate intense Lyman α (Lyα) emission like LAEs. We found that the bubbly structures produced are quite similar to the observed features in the Lyα surface brightness distribution of the extended LAEs. After 1 Gyr, the galaxies are dominated by stellar continuum radiation and then resemble the LBGs. At this point, the abundance of heavy elements appears to be solar. After 13 Gyr, these galaxies resemble present-day ellipticals.     

Quantification of the gas mass emitted during single explosions on Stromboli with the SO2 imaging camera

We performed measurements using an SO₂ imaging camera of the SO₂ gas mass emitted during five discrete explosive events on Stromboli volcano on 3 October 2006. The SO₂ gas mass released during discrete explosions was 15–40 kg per explosion, producing 3–8% of the total daily SO₂ gas emission, demonstrating that in terms of gas flux Strombolian explosions are a second-order phenomenon compared with quiescent degassing. Using the typical gas composition measured with OP-FTIR allows us to determine the total gas mass released during an explosion as 360–960 kg with a volume of 1500–4100 m³ at 1 bar. At the probable source pressure of gas slug formation of 75 MPa this gas amount would occupy a volume equivalent to a sphere with a radius of 0.8–1 m, comparable with estimates of Stromboli's conduit geometry.     

Petrology of peridotite and garnet clinopyroxenite of the Mt. Higasi-Akaisi mass,central Sikoku,Japan — Subsolidus relation of anhydrous phases

The mineralogy of anhydrous minerals of peridotite and garnet clinopyroxenite of the Mt. Higasi-Akaisi peridotite mass, Japan, is described. The subsolidus equilibria among garnet, clinopyroxene, orthopyroxene and olivine are discussed in terms of composition range of solid solutions and of Fe-Mg partition. It is concluded that the anydrous minerals of this mass equilibrated at lower temperatures than any of well studied peridotite-garnet clinopyroxenite association. The tentative estimation gives 5–600° C and 7–13 Kb as the physical conditions of equilibration. Comparison with similar associations from other occurrences and geological implications are briefly discussed.     

A weakly non-gaussian model of wave height distribution for random wave train

The wave height distribution with Edgeworth’s form of a cumulative expansion of probability density function (PDF) of surface elevation are investigated. The results show that a non-Gaussian model of wave height distribution reasonably agrees with experimental data. It is discussed that the fourth order moment (kurtosis) of water surface elevation corresponds to the first order nonlinear correction of wave heights and is related with wave grouping.     

三丁基氧化锡(TBTO)对太平洋牡蛎性成熟的影响

利用流水饲养法研究了不同浓度的三丁基氧化锡 (0 .5 μg/ L和 1.0 μg/ L TBTO)对太平洋牡蛎卵巢中卵母细胞直径、RNA/ DNA比、蛋白质和卵黄蛋白含量的影响。卵母细胞径的增长在0 .5 μg/ L实验组受到阻碍 ,并随着 TBTO浓度的增大而更加明显。TBTO暴露组的 RNA/ DNA比在精巢中无明显变化 ,但在卵巢中显著低于对照组。 TBTO暴露组的卵巢中蛋白质和卵黄蛋白含量显示了与 RNA/ DNA比相同的变化趋势 ,表明 TBTO的积累阻碍卵黄蛋白的合成。TBTO暴露4 2 d采集的牡蛎样品中出现 3个雌雄同体 ,暗示 TBTO可能引起牡蛎发生性转变进而产生雌雄同体