Enceladus: The likely dominant nitrogen source in Saturn's magnetosphere

The spatial distribution of N⁺ in Saturn's magnetosphere obtained from Cassini Plasma Spectrometer (CAPS) data can be used to determine the spatial distribution and relative importance of the nitrogen sources for Saturn's magnetosphere. We first summarize CAPS data from 15 orbits showing the spatial and energy distribution of the nitrogen component of the plasma. This analysis re-enforces our earlier discovery [Smith, H.T., Shappirio, M., Sittler, E.C., Reisenfeld, D., Johnson, R.E., Baragiola, R.A., Crary, F.J., McComas, D.J., Young, D.T., 2005. Geophys. Res. Lett. 32 (14). L14S03] that Enceladus is likely the dominant nitrogen source for Saturn's inner magnetosphere. We also find a sharp enhancement in the nitrogen ion to water ion ratio near the orbit of Enceladus which, we show, is consistent with the presence of a narrow Enceladus torus as described in [Johnson, R.E., Liu, M., Sittler Jr., E.C., 2005. Geophys. Res. Lett. 32. L24201]. The CAPS data and the model described below indicate that N⁺ ions are a significant fraction of the plasma in this narrow torus. We then simulated the combined Enceladus and Titan nitrogen sources using the CAPS data as a constraint. This simulation is an extension of the model we employed earlier to describe the neutral tori produced by the loss of nitrogen from Titan [Smith, H.T., Johnson, R.E., Shematovich, V.I., 2004. Geophys. Res. Lett. 31 (16). L16804]. We show that Enceladus is the principal nitrogen source in the inner magnetosphere but Titan might account for a fraction of the observed nitrogen ions at the largest distances discussed. We also show that the CAPS data is consistent with Enceladus being a molecular nitrogen source with a nitrogen to water ratio roughly consistent with INMS [Waite, J.H., and 13 colleagues, 2006. Science 311 (5766), 1419-1422], but out-gassing of other nitrogen-containing species, such as ammonia, cannot be ruled out.     

Raman confirmation of microdiamond in the Svartberget Fe‐Ti type garnet peridotite,Western Gneiss Region,Western Norway

Ultra‐high pressure metamorphic rocks have been found worldwide. The volume and areal extent of an exhumed UHPM domain are important for understanding the geodynamic mechanisms responsible for the high pressure and relatively medium temperature conditions needed for their creation. We report here Raman microspectroscopical data that prove the existence of microdiamonds at the Svartberget Fe‐Ti type peridotite locality in the Western Gneiss Region of Norway. Raman microscopy of two carbon microinclusions belonging to polyphase inclusion assemblages included in garnets from a garnet‐phlogopite websterite vein yielded a sharp, narrow, intense peak at 1332 cm^?1, characteristic of diamond. The diamond is associated with polyphase solid inclusions possibly originating from supercritical, dense, H‐C‐N‐O‐F‐P‐S‐Cl fluids. Lithological, textural and geochronological evidence points towards a Caledonian origin of the trapped fluid and subsequent diamond formation.     

Dawn Mission to Vesta and Ceres

The initial exploration of any planetary object requires a careful mission design guided by our knowledge of that object as gained by terrestrial observers. This process is very evident in the development of the Dawn mission to the minor planets 1 Ceres and 4 Vesta. This mission was designed to verify the basaltic nature of Vesta inferred both from its reflectance spectrum and from the composition of the howardite, eucrite and diogenite meteorites believed to have originated on Vesta. Hubble Space Telescope observations have determined Vesta’s size and shape, which, together with masses inferred from gravitational perturbations, have provided estimates of its density. These investigations have enabled the Dawn team to choose the appropriate instrumentation and to design its orbital operations at Vesta. Until recently Ceres has remained more of an enigma. Adaptive-optics and HST observations now have provided data from which we can begin to confidently plan the mission. These observations reveal a rotationally symmetric body with little surface relief, an ultraviolet bright point that can be used as a control point for determining the pole and anchoring a geographic coordinate system. They also reveal albedo and color variations that provide tantalizing hints of surface processes.     

Closure of a hyperextended system in an orogenic lithospheric pop‐up,Western Pyrenees: The role of mantle buttressing and rift structural inheritance

The Early Cretaceous hyperextended Mauléon rift is localized in the north‐western Pyrenean orogen. We infer the Tertiary evolution of the Mauléon basin through the restoration of a 153‐km‐long crustal‐scale balanced cross‐section of the Pyrenean belt, which documents at least 67 km (31%) of orogenic shortening in the Western Pyrenees. Initial shortening, accommodated through inversion of inherited crustal structures, led to formation of a pop‐up structure, in which the opposite edges underwent similar shortening with different tectonic reactivation styles, localized versus. distributed. Underthrusting of the Iberian margin accommodated further convergence, forming the Axial Zone antiformal stack of crustal nappes within a lithospheric pop‐up. Thin‐skinned and thick‐skinned structures propagated outward from the heart of this pop‐up, a block of strong mantle acting as a buttress inhibiting complete inversion of the Mauléon rift basin.     

基于证据理论的聚类集成方法

单个聚类方法得到的结果会存在不稳定性等问题,为了克服这些问题,本文在证据理论（又称为信任函数理论）的基础上提出了一种新的聚类集成方法.多数情况下,聚类集成方法主要包含2个关键步骤：得到一组基划分,以及结合基划分得到最终聚类结果,本文的方法重点考虑第2步.在第1步得到基划分之后,将其转换成一种中间表示,可以称这种中间表示为关系表示.在证据理论中,我们认为得到的关系表示是不可靠的,可以用折扣过程对关系表示进行预处理,然后就可以用不同的结合法则融合关系表示.从融合后的关系表示中提取信任矩阵或似然矩阵,将其视为样本间的互相关矩阵.为了能够充分利用样本间的传递性,将得到的互相关矩阵视为一个模糊关系,对其做传递闭包处理,从而得到一个模糊等价关系.将模糊的等价关系视为新的相似性数据,用能够处理相似性数据的聚类方法得到最终的结果.通过实验,表明了该聚类集成方法的稳定性和有效性.     

Geomorphology of a modern carbonate slope system and associated sedimentary processes: Example of the giant Great Abaco Canyon,Bahamas

The large acoustic data set acquired during the Carambar cruises is composed of high resolution bathymetry, backscatter data and very‐high resolution seismic lines which allow for an overview of the morphology and sediment transfer processes from the shallow upper slope to the abyssal plain of a modern carbonate system: the north‐eastern slope of the Little Bahama Bank. Surficial distribution of the acoustic facies and echofacies reflects a wide variety of sedimentary processes along and across the slope. The western sector of the Little Bahama Bank is dominated by depositional processes whereas its eastern sector, which is incised in the lower slope by giant canyons, is affected by erosion and bypass processes. Datasets suggest that currents play an important role both in along‐slope sedimentary processes and in the abyssal plain. The Antilles Current appears to affect a large part of the middle and lower slopes. The absence of sizeable present‐day channel/levée complexes or lobes at the mouth of the canyon – revealed by the bathymetric map – indicates that the southward flowing Deep Western Boundary Current influences modern abyssal sediment deposition. Based on depositional processes and indicators of canyon maturity observed in facies distribution, the current study proposes that differential subsidence affects the eastern versus western part of the bank. The morphology of the Great Abaco Canyon and Little Abaco Canyon, which extend parallel to the platform, and the Little Bahama Bank slope appears to be related to the Great Abaco Fracture Zone.