Seep mounds on the Southern Vøring Plateau (offshore Norway)

Multidisciplinary study of seep-related structures on Southern Vøring Plateau has been performed during several UNESCO/IOC TTR cruises on R/V Professor Logachev. High-resolution sidescan sonar and subbottom profiler data suggest that most of the studied fluid discharge structures have a positive relief at their central part surrounded by depression. Our data shows that the present day fluid activity is concentrated on the top of these “seep mounds”. Number of high hydrocarbon (HC) gas saturated sediment cores and 5 cores with gas hydrate presence have been recovered from these structures. δ¹³C of methane (between −68 and −94.6‰ VPDB) and dry composition of the gas points to its biogenic origin. The sulfate depletion generally occurs within the upper 30–200 cm bsf and usually coincides with an increase of methane concentration. Pore water δ¹⁸O ranges from 0.29 to 1.14‰ showing an overall gradual increase from bottom water values (δ¹⁸O ∼ 0.35‰). Although no obvious evidence of fluid seepage was observed during the TV surveys, coring data revealed a broad distribution of living Pogonophora and bacterial colonies on sea bottom inside seep structures. These evidences point to ongoing fluid activity (continuous seepage of methane) through these structures. From other side, considerable number and variety of chemosynthetic macro fauna with complete absence of living species suggest that present day level of fluid activity is significantly lower than it was in past. Dead and subfossil fauna recovered from various seep sites consist of solemyid (Acharax sp.), thyasirid and vesicomyid (cf. Calyptogena sp.) bivalves belonging to chemosymbiotic families. Significant variations in δ¹³C (−31.6‰ to −59.2‰) and δ¹⁸O (0.42‰ and 6.4‰) of methane-derived carbonates collected from these structures most probably related to changes in gas composition and bottom water temperature between periods of their precipitation. This led us to ideas that: (1) seep activity on the Southern Vøring Plateau was started with large input of the deep thermogenic gas and gradually decries in time with increasing of biogenic constituent; (2) authigenic carbonate precipitation started at the near normal deep sea environments with bottom water temperature around +5 °C and continues with gradual cooling up to negative temperatures recording at present time.     

The dark matter environment of the Abell 901/902 supercluster: a weak lensing analysis of the HST STAGES survey

We present a high-resolution dark matter reconstruction of the   z = 0.165  Abell 901/902 supercluster from a weak lensing analysis of the Hubble Space Telescope STAGES survey. We detect the four main structures of the supercluster at high significance, resolving substructure within and between the clusters. We find that the distribution of dark matter is well traced by the cluster galaxies, with the brightest cluster galaxies marking out the strongest peaks in the dark matter distribution. We also find a significant extension of the dark matter distribution of Abell 901a in the direction of an infalling X-ray group Abell 901α. We present mass, mass-to-light and mass-to-stellar mass ratio measurements of the structures and substructures that we detect. We find no evidence for variation of the mass-to-light and mass-to-stellar mass ratio between the different clusters. We compare our space-based lensing analysis with an earlier ground-based lensing analysis of the supercluster to demonstrate the importance of space-based imaging for future weak lensing dark matter 'observations'.     

Fault architecture in the Main Ethiopian Rift and comparison with experimental models: Implications for rift evolution and Nubia–Somalia kinematics

The Main Ethiopian Rift (MER) offers a complete record of the time–space evolution of a continental rift. We have characterized the brittle deformation in different rift sectors through the statistical analysis of a new database of faults obtained from the integration between satellite images and digital elevation models, and implemented with field controls. This analysis has been compared with the results of lithospheric-scale analogue models reproducing the kinematical conditions of orthogonal and oblique rifting. Integration of these approaches suggests substantial differences in fault architecture in the different rift sectors that in turn reflect an along-axis variation of the rift development and southward decrease in rift evolution. The northernmost MER sector is in a mature stage of incipient continental rupture, with deformation localised within the rift floor along discrete tectono-magmatic segments and almost inactive boundary faults. The central MER sector records a transitional stage in which migration of deformation from boundary faults to faults internal to the rift valley is in an incipient phase. The southernmost MER sector is instead in an early continental stage, with the largest part of deformation being accommodated by boundary faults and almost absent internal faults. The MER thus records along its axis the typical evolution of continental rifting, from fault-dominated rift morphology in the early stages of extension toward magma-dominated extension during break-up. The extrapolation of modelling results suggests that a variable rift obliquity contributes to the observed along-axis variations in rift architecture and evolutionary stage, being oblique rifting conditions controlling the MER evolution since its birth in the Late Miocene in relation to a constant post ca. 11 Ma ~ N100°E Nubia–Somalia motion.     

The A and B mica layers and the crystal structure of sheet silicates

A discussion of the transition from the ideal hexagonal mica structure to the ideal ditrigonal one, leads to the conclusion that the single mica layer may have two different structures (labelled A and B). The recent literature data show that both the A and B structures have been detected in some triocahedral layer lattice silicates found in nature. An examination of the structural stability of the A and B structures suggests that the last one may not be realized by dioctahedral layer lattice silicates. The concept of two structurally different mica layers, which however have the same lattice constants, greatly improves the understanding of polymorphism and twin laws in layer lattice silicates.The structural features of the tetrahedral sheet, octahedral sheet and interlayer region are carefully examined. Thus we can reach the following conclusions: the tetrahedal sheet is not entirely free to reduce its lateral dimensions by the mechanism of tetrahedal rotation owing to the repulsion among O_bas atoms; the octahedral sheet in layer lattice silicates, may increase or reduce its lateral dimensions as compared to the lateral dimensions it has in the hydroxide minerals; the interlayer region is characterized by a regular octahedral coordination of the O_bas around the interlayer cation. On the ground of these conclusions, new structural models for some selected layer lattice silicates are proposed.Notations O_bas basal oxygen atoms of the (Al, Si)O₄ tetrahedra - O_ap apical oxygen atoms of the (Al, Si)O₄ tetrahedra - b _tetr b dimension which the tetrahedral sheet would assume if unconstrained - b _oct b dimension which the octahedral sheet has in the hydroxide minerals - b _obs observed value of b - c _oct ^* thickness of the octahedral sheet - d _o distance between an octahedral cation and an O_ap atom - d _int distance between an interlayer cation and an O_bas atom - average tetrahedral rotation from ideal hexagonal symmetry     

Inverse compton emission of gamma rays near the pulsar surface

The physical conditions near pulsar surface that might give rise to gamma ray emission from Crab and Vela pulsars are not yet well understood. Here I suggest that, in the context of the vacuum discharge mechanism proposed by Ruderman and Sutherland (1975), gamma rays are produced by inverse Compton scattering of secondary electrons with the thermal radiation of the star surface as well as for curvature and synchrotron radiation. It is found that inverse Compton scattering is relevant if the neutron star surface temperature is greater than 10⁶K or if the polar cap temperature is of the order of 5×10⁶K. Inverse Compton scattering in anisotropic photon fields and Klein-Nishina regime is here carefully considered.     

Two paleoecological histories spanning the period of human settlement in southeastern Brazil

The absence of human occupation sites in southeastern Brazil during the mid Holocene has been referred to as the 'Archaic Gap' (8970–1940 cal. a BP) and is predicted to have resulted from increased aridity. A ca. 14 000 cal. a pollen history from two well‐dated lake sediment cores located within the archeological district of Lagoa Santa, in the State of Minas Gerais, southeastern Brazil, was used to test this hypothesis. Our analyses indicated that the present cerrado and tropical semi‐deciduous forest mosaic persisted throughout the mid Holocene, until ca. 5500 cal. a BP, and the Lagoa Santa region did not experience especially dry conditions during the Holocene period. The early Holocene pollen spectra contained an assemblage of cold‐adapted taxa such as Podocarpus, Myrsine and Araucaria, co‐occurring with taxa from cerrado, e.g. Caryocar. A replacement of cold taxa by the modern cerrado–semi‐deciduous forest vegetation took place progressively, but appears to have been completed by the mid Holocene. No evidence of sustained drought was found in sedimentation or forest composition, nor any prolonged dry event in the study region. Holocene dryness as an explanation for the abandonment of Lagoa Santa region is not supported by the palynological analyses conducted in this study. Rather it is suggested that unpredictable climate may have underlain that abandonment. Copyright © 2012 John Wiley & Sons, Ltd.     

Nonlinear Dynamic Response of HDRB and Hybrid HDRB-Friction Sliders Base Isolation Systems

The isolation systems are usually made of rubber bearings that are sometimes coupled in hybrid combination with frictional devices; this is the case of an in-site experimental campaign, performed on a base isolated apartment building in Rapolla (south of Italy). Several dropout tests at initial displacements up to 17cm allowed to obtain in-site information on the true dynamic response of the isolation system (building and isolators). The tests carried out allow a comparison between the free vibration responses of a building, isolated by using a 28 HDRB isolation system only, or an HDRB-Friction Sliders Hybrid one. The paper highlights the main differences of the response in the superstructure (the structure over the isolation system) obtained by using only HDRB isolation system, or the Hybrid one (HDRB and Friction Sliders in parallel system). Analysis and comparisons of experimental data, show the influence of nonlinearities on structural higher modes amplification, especially observed by using the higher nonlinear Hybrid isolation system. Tests results confirm that, in the case of a regular superstructure, like the Rapolla building, the isolation system nonlinearities influence the structural response.     

基于GIS/RS的洪湖东分洪区洪水风险制图

本文计算了洪湖东分洪区洪灾损失.洪水风险带以模拟的洪水淹没深度表示.这是洪水风险综合评价模型的基础.本项研究基于GIS为基础的水动力模型计算洪水淹没深度;并以GIS/RS为基础建立了单位洪水风险评价模型,计算不同洪水风险带的直接损失.研究表明,综合洪水风险评价模型在长江流域应用是可行的.     

Differences in grain growth of calcite: a field-based modeling approach

Normal grain growth of calcite was investigated by combining grain size analysis of calcite across the contact aureole of the Adamello pluton, and grain growth modeling based on a thermal model of the surroundings of the pluton. In an unbiased model system, i.e., location dependent variations in temperature-time path, 2/3 and 1/3 of grain growth occurs during pro- and retrograde metamorphism at all locations, respectively. In contrast to this idealized situation, in the field example three groups can be distinguished, which are characterized by variations in their grain size versus temperature relationships: Group I occurs at low temperatures and the grain size remains constant because nano-scale second phase particles of organic origin inhibit grain growth in the calcite aggregates under these conditions. In the presence of an aqueous fluid, these second phases decay at a temperature of about 350 °C enabling the onset of grain growth in calcite. In the following growth period, fluid-enhanced group II and slower group III growth occurs. For group II a continuous and intense grain size increase with T is typical while the grain growth decreases with T for group III. None of the observed trends correlate with experimentally based grain growth kinetics, probably due to differences between nature and experiment which have not yet been investigated (e.g., porosity, second phases). Therefore, grain growth modeling was used to iteratively improve the correlation between measured and modeled grain sizes by optimizing activation energy (Q), pre-exponential factor (k₀) and grain size exponent (n). For n=2, Q of 350 kJ/mol, k₀ of 1.7×10²¹ mⁿs^–1 and Q of 35 kJ/mol, k₀ of 2.5×10^-5 mⁿs^–1 were obtained for group II and III, respectively. With respect to future work, field-data based grain growth modeling might be a promising tool for investigating the influences of secondary effects like porosity and second phases on grain growth in nature, and to unravel differences between nature and experiment.Editorial responsibility: J. Hoefs     

Preliminary assessment of the ATHENA/WFI non-X-ray background

We present a preliminary assessment of the non-X-ray background for the WFI on board ATHENA conducted at IAAT in the context of the collaborative background and radiation damage working group activities. Our main result is that in the baseline configuration originally assumed for the camera the requirement on the level of non-X-ray background could not be met. In light of the results of Geant4 simulations we propose and discuss a possible optimization of the camera design and pinpoint some open issues to be addressed in the next phase of investigation. One of these concerns the possible contribution to the non-X-ray background from soft protons and ions funneled to the focal plane through the optics. This is not quantified at this stage, here we just briefly report on our ongoing activities aimed at validating the mechanisms of proton scattering at grazing incidence.