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971.
Francien Peterse Jung-Hyun Kim Stefan Schouten Dorthe Klitgaard Kristensen Nalân Koç Jaap S. Sinninghe Damsté 《Organic Geochemistry》2009,40(6):692-699
Branched glycerol dialkyl glycerol tetraethers (GDGTs) are membrane lipids of unknown bacteria that are ubiquitous in soil and peat. Two indices based on the distribution of these lipids in soils, the Cyclization of Branched Tetraethers (CBT) and the Methylation of Branched Tetraethers (MBT) indices have been shown to correlate with soil pH, and mean annual air temperature (MAT) and soil pH, respectively, and can be used to reconstruct MAT in palaeoenvironments. To verify the extent to which branched GDGTs in marine sediments reflect the distribution pattern on land and whether these proxies are applicable for palaeoclimate reconstruction in high latitude environments with a MAT of <0 °C, we compared the branched GDGT distribution in Svalbard soils and nearby fjord sediments. Although branched GDGT concentrations in the soil are relatively low (0.02–0.95 μg/g dry weight (dw)) because of the cold climate and the short growing season, reconstructed MATs based on the MBT/CBT proxy are ca. ?4 °C, close to the measured MAT (ca. ?6 °C). Concentrations of branched GDGTs (0.01–0.20 μg/g dw) in fjord sediments increased towards the open ocean and the distribution was strikingly different from that in soil, i.e. dominated by GDGTs with one cyclopentane moiety. This resulted in MBT/CBT-reconstructed MAT values of 11–19 °C, well above measured MAT. The results suggest that at least part of the branched GDGTs in marine sediments in settings with a low soil organic matter (OM) input may be produced in situ. In these cases, the application of the MBT/CBT palaeothermometer will generate unrealistic MAT reconstructions. The MBT/CBT proxy should therefore only be used at sites with a substantial input of soil OM relative to the amount of marine OM, i.e. at sites close to the mouth of rivers with a catchment area where sufficient soil formation takes place and the soil thus contains substantial amounts of branched GDGTs. 相似文献
972.
Fifty years of organisational change in container shipping: regional shift and the role of family firms 总被引:1,自引:0,他引:1
Spectacular growth has marked the industry initiated by Malcolm McLean with the sailing of the Ideal-X in 1956. While the growth of container shipping has been typically seen in terms of technological advances, increasing vessel
capacity, traffic growth, financial performance and competitiveness, it has been shaped also by organisational transformations.
This paper provides an overview of the major companies that make up the container shipping industry, tracing the rapid adoption
of containerisation by American carriers to its diffusion to Europe and then Asia. While several carriers belong to business
conglomerates, the most dynamic in recent years have been those that are those that possess a family structure. About 12 of
the present top 20 carriers are largely family controlled, including 4 out of the top 5. Unlike other capital intensive industries,
where the power has shifted towards corporate governance, the container shipping industry retains a strong individualistic
entrepreneurial character. At a time when North American ownership in container shipping is no more, the spirit of innovation
began 50 years ago by an American visionary is still evident in the entrepreneurial dynamism of many of the industry leaders. 相似文献
973.
We present here a numerical modelling study of dislocations in perovskite CaTiO3. The dislocation core structures and properties are calculated through the Peierls–Nabarro model using the generalized stacking
fault (GSF) results as a starting model. The GSF are determined from first-principles calculations using the VASP code. The
dislocation properties such as collinear, planar core spreading and Peierls stresses are determined for the following slip
systems: [100](010), [100](001), [010](100), [010](001), [001](100), [001](010),
and All dislocations exhibit lattice friction, but glide appears to be easier for [100](010) and [010](100).
[001](010) and [001](100) exhibit collinear dissociation. Comparing Peierls stresses among tausonite (SrTiO3), perovskite (CaTiO3) and MgSiO3 perovskite demonstrates the strong influence of orthorhombic distortions on lattice friction. However, and despite some quantitative
differences, CaTiO3 appears to be a satisfactory analogue material for MgSiO3 perovskite as far as dislocation glide is concerned. 相似文献
974.
975.
Stress Measurement by Overcoring at Shallow Depths in a Rock Slope: the Scattering of Input Data and Results 总被引:1,自引:0,他引:1
C. Clément V. Merrien-Soukatchoff C. Dünner Y. Gunzburger 《Rock Mechanics and Rock Engineering》2009,42(4):585-609
This paper describes a field experiment of stress measurement using the overcoring method performed in a rock slope, called
Rochers de Valabres (located in France’s Southern Alps Region), a field laboratory site prone to rockfalls. Six measurements were conducted at
shallow depths from the surface, moving deeper along a sub-horizontal borehole. The experiment was conducted in heterogeneous
and anisotropic gneiss, with the overcored rock elastic properties, as evaluated by biaxial and uniaxial tests, being widely
scattered. Since stress calculations are sensitive to all input data uncertainties, strain inversion was, thus, performed
using an experimental device and Monte Carlo simulations. The experimental device allows the assessment of rather broad confidence
intervals for both stress magnitude and orientation. The results indicate that the stress state in the surface area is quite
heterogeneous and may be correlated with topography. The measurements show a nonlinear stress distribution with distance to
the free surface, along with high values of principal stresses, despite the vicinity of the surface. Although influenced by
local topography, orientations of the principal computed stresses are characterized by a high turnover due to local heterogeneities.
The results are roughly in accordance to a 2D finite element model of the site. 相似文献
976.
Sébastien Couvidat S. P. Rajaguru Richard Wachter K. Sankarasubramanian Jesper Schou Philip H. Scherrer 《Solar physics》2012,278(1):217-240
The Helioseismic and Magnetic Imager (HMI) instrument onboard the Solar Dynamics Observatory produces line-of-sight (LOS) observables (Doppler velocity, magnetic-field strength, Fe i line width, line depth, and continuum intensity) as well as vector magnetic-field maps at the solar surface. The accuracy of LOS observables is dependent on the algorithm used to translate a sequence of HMI filtergrams into the corresponding observables. Using one hour of high-cadence imaging spectropolarimetric observations of a sunspot in the Fe i line at 6173 Å through the Interferometric Bidimensional Spectrometer installed at the Dunn Solar Telescope, and the Milne–Eddington inversion of the corresponding Stokes vectors, we test the accuracy of the observables algorithm currently implemented in the HMI data-analysis pipeline: the MDI-like algorithm. In an attempt to improve the accuracy of HMI observables, we also compare this algorithm to others that may be implemented in the future: a least-squares fit with a Gaussian profile, a least-squares fit with a Voigt profile, and the use of second Fourier coefficients in the MDI-like algorithm. 相似文献
977.
We present three-dimensional unsteady modeling and numerical simulations of a coronal active region, carried out within the
compressible single-fluid MHD approximation. We focus on AR 9077 on 14 July 2000, and the triggering of the X5.7 GOES X-ray
class “Bastille Day” flare. We simulate only the lower corona, although we include a virtual photosphere and chromosphere
below. The boundary conditions at the base of this layer are set using temperature maps from line intensities and line-of-sight
magnetograms (SOHO/MDI). From the latter, we generate vector magnetograms using the force-free approximation; these vector
magnetograms are then used to produce the boundary condition on the velocity field using a minimum energy principle (Longcope,
Astrophys. J.
612, 1181, 2004). The reconnection process is modeled through a dynamical hyper-resistivity which is activated when the current exceeds a
critical value (Klimas et al., J. Geophys. Res.
109, 2218, 2004). Comparing the time series of X-ray fluxes recorded by GOES with modeled time series of various mean physical variables
such as current density, Poynting energy flux, or radiative loss inside the active region, we can demonstrate that the model
properly captures the evolution of an active region over a day and, in particular, is able to explain the initiation of the
flare at the observed time. 相似文献
978.
Jaume Giné 《Astrophysics and Space Science》2012,337(1):483-486
In this paper we discuss the recently obtained relation between the Verlinde’s holographic model and the first phenomenological
Modified Newtonian dynamics. This gives also a promising possible explanation to the Pioneer anomaly. 相似文献
979.
Jürgen Oberst Valéry Lainey Christophe Le Poncin-Lafitte Veronique Dehant Pascal Rosenblatt Stephan Ulamec Jens Biele J?rn Spurmann Ralph Kahle Volker Klein Ulrich Schreiber Anja Schlicht Nicolas Rambaux Philippe Laurent Beno?t Noyelles Bernard Foulon Alexander Zakharov Leonid Gurvits Denis Uchaev Scott Murchie Cheryl Reed Slava G. Turyshev Jesus Gil Mariella Graziano Konrad Willner Kai Wickhusen Andreas Pasewaldt Marita W?hlisch Harald Hoffmann 《Experimental Astronomy》2012,34(2):243-271
GETEMME (Gravity, Einstein??s Theory, and Exploration of the Martian Moons?? Environment), a mission which is being proposed in ESA??s Cosmic Vision program, shall be launched for Mars on a Soyuz Fregat in 2020. The spacecraft will initially rendezvous with Phobos and Deimos in order to carry out a comprehensive mapping and characterization of the two satellites and to deploy passive Laser retro-reflectors on their surfaces. In the second stage of the mission, the spacecraft will be transferred into a lower 1500-km Mars orbit, to carry out routine Laser range measurements to the reflectors on Phobos and Deimos. Also, asynchronous two-way Laser ranging measurements between the spacecraft and stations of the ILRS (International Laser Ranging Service) on Earth are foreseen. An onboard accelerometer will ensure a high accuracy for the spacecraft orbit determination. The inversion of all range and accelerometer data will allow us to determine or improve dramatically on a host of dynamic parameters of the Martian satellite system. From the complex motion and rotation of Phobos and Deimos we will obtain clues on internal structures and the origins of the satellites. Also, crucial data on the time-varying gravity field of Mars related to climate variation and internal structure will be obtained. Ranging measurements will also be essential to improve on several parameters in fundamental physics, such as the Post-Newtonian parameter ?? as well as time-rate changes of the gravitational constant and the Lense-Thirring effect. Measurements by GETEMME will firmly embed Mars and its satellites into the Solar System reference frame. 相似文献
980.
Alvaro P. CRÓSTA César KAZZUO‐VIEIRA Lidia PITARELLO Christian KOEBERL Thomas KENKMANN 《Meteoritics & planetary science》2012,47(1):51-71
Abstract– Vargeão Dome (southern Brazil) is a circular feature formed in lava flows of the Lower Cretaceous Serra Geral Formation and in sandstones of the Paraná Basin. Even though its impact origin was already proposed in the 1980s, little information about its geological and impact features is available in the literature. The structure has a rim‐rim diameter of approximately 12 km and comprises several ring‐like concentric features with multiple concentric lineaments. The presence of a central uplift is suggested by the occurrence of deformed sandstone strata of the Botucatu and Pirambóia formations. We present the morphological/structural characteristics of Vargeão Dome, characterize the different rock types that occur in its interior, mainly brecciated volcanic rocks (BVR) of the Serra Geral Formation, and discuss the deformation and shock features in the volcanic rocks and in sandstones. These features comprise shatter cones in sandstone and basalt, as well as planar microstructures in quartz. A geochemical comparison of the target rock equivalents from outside the structure with the shocked rocks from its interior shows that both the BVRs and the brecciated sandstone have a composition largely similar to that of the corresponding unshocked lithologies. No traces of meteoritic material have been found so far. The results confirm the impact origin of Vargeão Dome, making it one of the largest among the rare impact craters in basaltic targets known on Earth. 相似文献