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241.
Marcel Zemp Ben Moore Joachim Stadel C. Marcella Carollo Piero Madau 《Monthly notices of the Royal Astronomical Society》2008,386(3):1543-1556
We present a simple and efficient method to set up spherical structure models for N -body simulations with a multimass technique. This technique reduces by a substantial factor the computer run time needed in order to resolve a given scale as compared to single-mass models. It therefore allows to resolve smaller scales in N -body simulations for a given computer run time. Here, we present several models with an effective resolution of up to 1.68 × 109 particles within their virial radius which are stable over cosmologically relevant time-scales. As an application, we confirm the theoretical prediction by Dehnen that in mergers of collisionless structures like dark matter haloes always the cusp of the steepest progenitor is preserved. We model each merger progenitor with an effective number of particles of approximately 108 particles. We also find that in a core–core merger the central density approximately doubles whereas in the cusp–cusp case the central density only increases by approximately 50 per cent. This may suggest that the central regions of flat structures are better protected and get less energy input through the merger process. 相似文献
242.
243.
Joachim Schmidt Lars Opgenoorth Jochen Martens Georg Miehe 《Quaternary Science Reviews》2011,30(15-16):1918-1925
Previous findings regarding the Last Glacial Maximum LGM summer temperature depression (maxΔT in July) on the Tibetan Plateau varied over a large range (between 0 and 9 °C). Geologic proxies usually provided higher values than palynological data. Because of this wide temperature range, it was hitherto impossible to reconstruct the glacial environment of the Tibetan Plateau. Here, we present for the first time data indicating that local neoendemics of modern species groups are promising proxies for assessing the LGM temperature depression in Tibet. We used biogeographical and phylogenetic data from small, wingless edaphous ground beetles of the genus Trechus, and from private juniper tree haplotypes. The derived values of the maxΔT in July ranged between 3 and 4 °C. Our data support previous findings that were based on palynological data. At the same time, our data are spatially more specific as they are not bound to specific archives. Our study shows that the use of modern endemics enables a detailed mapping of local LGM conditions in High Asia. A prerequisite for this is an extensive biogeographical and phylogenetic exploration of the area and the inclusion of additional endemic taxa and evolutionary lines. 相似文献
244.
Numerical simulation of Qiaotou Landslide deformation caused by drawdown of the Three Gorges Reservoir,China 总被引:6,自引:2,他引:4
Jiwei Jiang Dominik Ehret Wei Xiang Joachim Rohn Ling Huang Shaojun Yan Renneng Bi 《Environmental Earth Sciences》2011,62(2):411-419
Landslides located beside reservoirs tend to be unstable or are characterized by large deformation during the drawdown process.
This has been accepted by many experts. In this paper, we use Qiaotou Landslide, which is located beside the Three Gorges
Reservoir (TGR), as a typical case study to investigate and predict the deformation mechanism during the drawdown process
of TGR in detail. According to field investigation, the landslide mass is mainly composed of thick, loose silt and clay mixed
with fragments of rock. Bedrock is mainly composed of silty sandstone. Field and laboratory tests indicate that the landslide
mass has a high permeability coefficient. If the water level declines fast, intense seepage force may result. Based on these
data, we establish a three-dimensional geological model of Qiaotou Landslide by FLAC3D and perform a numerical simulation using the saturated–unsaturated fluid–solid coupling theory. For the simulation, we assume
that the drawdown from 175 to 145 m takes place with a speed of 25 cm/day, which is based on the extreme water level regulation
program of TGR. The simulation shows that this causes a significant deformation in the landslide mass and that the maximum
displacement within the landslide is 24.2 cm. During the drawdown process, the maximum displacement zone is shifting from
the upper part of the landslide where bedrock surface is steeper and thickness of loose deposits is less to the middle part
of the landslide where bedrock surface is less steep and thickness of loose deposits is higher. The deformation mechanism
indicates that in the early stage of the drawdown the deformation of the landslide mass is mainly caused by seepage and in
the later stage mainly by consolidation. 相似文献
245.
Till Neeff Zoltán Somogyi Corinna Schultheis Esther Mertens Joachim Rock Johannes Brötz 《Climate Policy》2013,13(2):203-212
This article reports experiences gathered in 12 developing countries in Latin America and Africa with capacity development for national GHG inventory systems. The national systems and their ability to deliver on measurement, reporting and verification (MRV) requirements is assessed using a scorecard that covers the transparency, accuracy, completeness, consistency, and comparability of the GHG inventory as well as its institutional set-up and management aspects. The analysis shows that a quantitative assessment of GHG inventory systems with a scorecard is feasible and useful, and could commonly be used for tracking progress in MRV capacity development.Policy relevanceA large number of capacity development initiatives are underway to advance national GHG inventory systems in developing countries, particularly in the land-use sector. These aim to promote the reliable MRV of GHG emissions and removals, which is expected to underpin developing countries’ contributions to global mitigation efforts, including through results-based payments. Although MRV is a cornerstone of climate change policy and despite widespread capacity gaps, there is little conclusive evidence about the effectiveness of such capacity development. This article relates the positive experience from one initiative, the Capacity Development for REDD+ project, which employed a novel, scorecard-based approach to results monitoring. Considerable progress is observed and provides reassurance regarding the soundness of development agencies’ significant investments in MRV. Disaggregating scores by countries and by underlying criteria also provides insights to prioritize further investments. 相似文献
246.
Markus Schleier Renneng Bi Joachim Rohn Dominik Ehret Wei Xiang 《Environmental Earth Sciences》2014,71(7):3007-3023
Increasing number of geohazards, like mass movements, is one of the main environmental impacts following the impoundment of the Yangtze River and its tributaries due to the inventory of the Three Gorges Dam hydroelectric power plant. Although many cities and settlements are endangered, no detailed hazard mapping is possible because of the huge size of the affected area. Due to strongly limited data availability, a robust landslide susceptibility model was established exemplarily for the Xiangxi catchment as one of the main tributaries. The analyses were limited to translational, rotational and combined landslides in soft rock sediments because these represent the main types of mass movement activity in this area. The qualitative landslide susceptibility analysis was carried out by a combination of frequency ratio analyses and a heuristic iterative index-based method using a Geographical Information System. As conditioning factors, the parameters lithology, slope angle, -aspect, -curvature, drainage buffer distance and land use were applied. To improve the objectivity of the index-based method, the results of frequency ratio analyses were taken into consideration to assess the importance of each factor. Model verification and evaluation by ground truth enable to improve the model by iterative calculations and to identify the best performance model. Results indicate that 89 % of all known landslides are located within areas showing high susceptibility according to the best performance model. The study demonstrates that a rather simple but robust model achieves good results and is applicable for regional landslide susceptibility analyses in mountainous areas with poor data availability. 相似文献
247.
248.
Anticlockwise pressure–temperature paths record Variscan upper‐plate exhumation: Example from micaschists of the Porto Vecchio region,Corsica
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Hans‐Joachim Massonne Gabriele Cruciani Marcello Franceschelli Giovanni Musumeci 《Journal of Metamorphic Geology》2018,36(1):55-77
To better understand the evolution of deep‐seated crust of the Variscan orogen in the Sardinia‐Corsica region, we studied garnet‐bearing micaschists which were sampled 3 km east and 15 km northeast of Porto Vecchio, south‐eastern Corsica. After a careful investigation of the textural relations and compositions of minerals, especially of zoned garnet, a P–T path was reconstructed using contoured P–T pseudosections. U–Th–Pb dating of monazite in the micaschists was undertaken with the electron microprobe. The micaschists from both localities were formed along similar anticlockwise P–T paths. The prograde branch of these paths starts at 3 kbar close to 600°C in the P–T field of sillimanite and reaches peak conditions at 7 kbar and 600 (15 km NE of Porto Vecchio) to 630°C (3 km E of Porto Vecchio). The metamorphism at peak P–T conditions happened c. 340 Ma based on low‐Y (<0.65 wt% Y2O3) monazite. Ages of monazite with high‐Y contents (>2 wt% Y2O3), which probably have formed before garnet, scatter around 362 Ma. The retrograde branch of the P–T paths passes through 4 kbar at ~550°C. We conclude that the micaschists belong to a common metasedimentary sequence, which extends over the Porto Vecchio region and is separated from other metamorphic rock sequences in the north and the south by major tectonic boundaries. This sequence had experienced peak pressures which are lower than those determined for metamorphic rocks, such as micaschist and gneiss, from north‐eastern Sardinia. At present, we favour a continent–continent collisional scenario with the studied metasedimentary sequence buried during the collisional event as part of the upper plate. The contemporaneous high‐P metamorphic rocks from NE Sardinia were part of the upper portion of the lower plate. The addressed rocks from both plates were exhumed in an exhumation channel. 相似文献
249.
Darren Reed Fabio Governato Thomas Quinn Jeffrey Gardner Joachim Stadel George Lake 《Monthly notices of the Royal Astronomical Society》2005,359(4):1537-1548
We use cosmological Λ cold dark matter (CDM) numerical simulations to model the evolution of the substructure population in 16 dark matter haloes with resolutions of up to seven million particles within the virial radius. The combined substructure circular velocity distribution function (VDF) for hosts of 1011 to 1014 M⊙ at redshifts from zero to two or higher has a self-similar shape, is independent of host halo mass and redshift, and follows the relation d n /d v = (1/8)( v cmax / v cmax,host )−4 . Halo to halo variance in the VDF is a factor of roughly 2 to 4. At high redshifts, we find preliminary evidence for fewer large substructure haloes (subhaloes). Specific angular momenta are significantly lower for subhaloes nearer the host halo centre where tidal stripping is more effective. The radial distribution of subhaloes is marginally consistent with the mass profile for r ≳ 0.3 r vir , where the possibility of artificial numerical disruption of subhaloes can be most reliably excluded by our convergence study, although a subhalo distribution that is shallower than the mass profile is favoured. Subhalo masses but not circular velocities decrease towards the host centre. Subhalo velocity dispersions hint at a positive velocity bias at small radii. There is a weak bias towards more circular orbits at lower redshift, especially at small radii. We additionally model a cluster in several power-law cosmologies of P ∝ kn , and demonstrate that a steeper spectral index, n , results in significantly less substructure. 相似文献
250.