Chemodynamical Modelling of Galaxy Formation and Evolution     

Peter Berczik  Gerhard Hensler  Christian Theis  Rainer Spurzem 《Astrophysics and Space Science》2002,281(1-2):297-300

We present our recently developed 3-dimensional chemodynamical code for galaxy evolution. This code follows the evolution of different galactic components like stars, dark matter and different components of the interstellar medium (ISM), i.e. a diffuse gaseous phase and the molecular clouds. Stars and dark matter are treated as collisionless N-body systems. The ISM is numerically described by a smoothed particle hydrodynamics (SPH) approach for the diffuse gas and a sticky particle scheme for the molecular clouds. Additionally, the galactic components are coupled by several phase transitions like star formation, stellar death or condensation and evaporation processes within the ISM. As an example we show the dynamical and chemical evolution of a star forming dwarf galaxy with a total baryonic mass of 2 ċ 10⁹ M_⊙. After a moderate collapse phase the stars and the molecular clouds follow an exponential radial distribution, whereas the diffuse gas shows a central depression as a result of stellar feedback. The metallicities of the galactic components behave quite differently with respect to their temporal evolution as well as their radial distribution. Especially, the ISM is at no stage well mixed. This revised version was published online in September 2006 with corrections to the Cover Date.  相似文献   

A deep kinematic survey of planetary nebulae in the Andromeda galaxy using the Planetary Nebula Spectrograph     

H. R. Merrett  M. R. Merrifield  N. G. Douglas  K. Kuijken  A. J. Romanowsky  N. R. Napolitano  M. Arnaboldi  M. Capaccioli  K. C. Freeman  O. Gerhard  L. Coccato  D. Carter  N. W. Evans  M. I. Wilkinson  C. Halliday  T. J. Bridges 《Monthly notices of the Royal Astronomical Society》2006,369(1):120-142

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Mass-to-light ratio gradients in early-type galaxy haloes   总被引：1，自引：0，他引：1  

N. R. Napolitano  M. Capaccioli  A. J. Romanowsky  N. G. Douglas  M. R. Merrifield  K. Kuijken  M. Arnaboldi  O. Gerhard  K. C. Freeman 《Monthly notices of the Royal Astronomical Society》2005,357(2):691-706

Owing to the fact that the near future should see a rapidly expanding set of probes of the halo masses of individual early-type galaxies, we introduce a convenient parameter for characterizing the halo masses from both observational and theoretical results:  ∇_ℓϒ  , the logarithmic radial gradient of the mass-to-light ratio. Using halo density profiles from Λ-cold dark matter (CDM) simulations, we derive predictions for this gradient for various galaxy luminosities and star formation efficiencies  ε_SF  . As a pilot study, we assemble the available  ∇_ℓϒ  data from kinematics in early-type galaxies – representing the first unbiased study of halo masses in a wide range of early-type galaxy luminosities – and find a correlation between luminosity and  ∇_ℓϒ  , such that the brightest galaxies appear the most dark-matter dominated. We find that the gradients in most of the brightest galaxies may fit in well with the ΛCDM predictions, but that there is also a population of fainter galaxies whose gradients are so low as to imply an unreasonably high star formation efficiency  ε_SF > 1  . This difficulty is eased if dark haloes are not assumed to have the standard ΛCDM profiles, but lower central concentrations.  相似文献   

CODE’s five-system orbit and clock solution—the challenges of multi-GNSS data analysis   总被引：1，自引：1，他引：0  

Lars Prange  Etienne Orliac  Rolf Dach  Daniel Arnold  Gerhard Beutler  Stefan Schaer  Adrian Jäggi 《Journal of Geodesy》2017,91(4):345-360

This article describes the processing strategy and the validation results of CODE’s MGEX (COM) orbit and satellite clock solution, including the satellite systems GPS, GLONASS, Galileo, BeiDou, and QZSS. The validation with orbit misclosures and SLR residuals shows that the orbits of the new systems Galileo, BeiDou, and QZSS are affected by modelling deficiencies with impact on the orbit scale (e.g., antenna calibration, Earth albedo, and transmitter antenna thrust). Another weakness is the attitude and solar radiation pressure (SRP) modelling of satellites moving in the orbit normal mode—which is not yet correctly considered in the COM solution. Due to these issues, we consider the current state COM solution as preliminary. We, however, use the long-time series of COM products for identifying the challenges and for the assessment of model-improvements. The latter is demonstrated on the example of the solar radiation pressure (SRP) model, which has been replaced by a more generalized model. The SLR validation shows that the new SRP model significantly improves the orbit determination of Galileo and QZSS satellites at times when the satellite’s attitude is maintained by yaw-steering. The impact of this orbit improvement is also visible in the estimated satellite clocks—demonstrating the potential use of the new generation satellite clocks for orbit validation. Finally, we point out further challenges and open issues affecting multi-GNSS data processing that deserves dedicated studies.  相似文献   

Experimental Melting of Carbonated Peridotite at 6-10 GPa   总被引：2，自引：0，他引：2  

Brey  Gerhard P.; Bulatov  Vadim K.; Girnis  Andrei V.; Lahaye  Yann 《Journal of Petrology》2008,49(4):797-821

Partial melting of magnesite-bearing peridotites was studiedat 6–10 GPa and 1300–1700°C. Experiments wereperformed in a multianvil apparatus using natural mineral mixesas starting material placed into olivine containers and sealedin Pt capsules. Partial melts originated within the peridotitelayer, migrated outside the olivine container and formed poolsof quenched melts along the wall of the Pt capsule. This allowedthe analysis of even small melt fractions. Iron loss was nota problem, because the platinum near the olivine container becamesaturated in Fe as a result of the reaction Fe₂SiO₄^Ol = Fe^Fe–Ptalloy + FeSiO₃^Opx + O₂. This reaction led to a gradual increasein oxygen fugacity within the capsules as expressed, for example,in high Fe³⁺ in garnet. Carbonatitic to kimberlite-like meltswere obtained that coexist with olivine + orthopyroxene + garnet± clinopyroxene ± magnesite depending on P–Tconditions. Kinetic experiments and a comparison of the chemistryof phases occasionally grown within the melt pools with thosein the residual peridotite allowed us to conclude that the meltshad approached equilibrium with peridotite. Melts in equilibriumwith a magnesite-bearing garnet lherzolite are rich in CaO (20–25wt %) at all pressures and show rather low MgO and SiO₂ contents(20 and 10 wt %, respectively). Melts in equilibrium with amagnesite-bearing garnet harzburgite are richer in SiO₂ andMgO. The contents of these oxides increase with temperature,whereas the CaO content becomes lower. Melts from magnesite-freeexperiments are richer in SiO₂, but remain silicocarbonatitic.Partitioning of trace elements between melt and garnet was studiedin several experiments at 6 and 10 GPa. The melts are very richin incompatible elements, including large ion lithophile elements(LILE), Nb, Ta and light rare earth elements. Relative to theresidual peridotite, the melts show no significant depletionin high field strength elements over LILE. We conclude fromthe major and trace element characteristics of our experimentalmelts that primitive kimberlites cannot be a direct productof single-stage melting of an asthenospheric mantle. They rathermust be derived from a previously depleted and re-enriched mantleperidotite. KEY WORDS: multianvil; carbonatite melt; peridotite; kimberlite; element partitioning  相似文献   

Foreword: The Roles of Petrology and Experimental Petrology in Understanding Global Tectonics     

Yaxley  Gregory M.; Brey  Gerhard P. 《Journal of Petrology》2008,49(4):587-589

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Statistical Relational Learning of Grammar Rules for 3D Building Reconstruction          下载免费PDF全文

Youness Dehbi  Fabian Hadiji  Gerhard Gröger  Kristian Kersting  Lutz Plümer 《Transactions in GIS》2017,21(1):134-150

The automatic interpretation of 3D point clouds for building reconstruction is a challenging task. The interpretation process requires highly structured models representing semantics. Formal grammars can describe structures as well as the parameters of buildings and their parts. We propose a novel approach for the automatic learning of weighted attributed context‐free grammar rules for 3D building reconstruction, supporting the laborious manual design of rules. We separate structure from parameter learning. Specific Support Vector Machines (SVMs) are used to generate a weighted context‐free grammar and predict structured outputs such as parse trees. The grammar is extended by parameters and constraints, which are learned based on a statistical relational learning method using Markov Logic Networks (MLNs). MLNs enforce the topological and geometric constraints. MLNs address uncertainty explicitly and provide probabilistic inference. They are able to deal with partial observations caused by occlusions. Uncertain projective geometry is used to deal with the uncertainty of the observations. Learning is based on a large building database covering different building styles and façade structures. In particular, a treebank that has been derived from the database is employed for structure learning.  相似文献   

The Effect of the Canadian Shield on Cloud-to-Ground Lightning Density     

Daniel Brown  Gerhard Reuter 《大气与海洋》2017,55(3):133-143

The Canadian Shield is a large area of exposed bedrock that covers a significant portion of Canada. The focus of this research is on the Canadian Shield in northeastern regions of the Canadian Prairie provinces, the Northwest Territories, and northwestern Ontario. Observations of cloud-to-ground lightning flashes show a distinct reduction in lightning density when crossing the southern boundary of the Canadian Shield. Statistical tests were used to determine whether there was a statistically significant change between the average cloud-to-ground lightning density gradient near the Canadian Shield and away from it. Most regions had a statistically significant change at the 95% confidence level across the boundary. However, regions that contained large lakes or significant topography did not, suggesting that the large open water and rough topography have a greater effect than the Canadian Shield.

Three reasons for the distinct change across the Canadian Shield were explored: less lightning is detected, less lightning occurs with the same number of thunderstorms, and less lightning occurs because fewer thunderstorms occur. Some evidence suggested that less lightning is detected because the Canadian Shield has lower electrical conductivity. The low conductivity distorts the lightning waveform and contributes to higher errors and lower detection efficiency. There is also some evidence that a sharp change in land cover from lusher, higher transpiring forest to sparser lower transpiring forest could be reducing the instability causing fewer, weaker thunderstorms.  相似文献   

Holocene ice dynamics and bottom-water formation associated with Cape Darnley polynya activity recorded in Burton Basin,East Antarctica     

Andreas Borchers  Elisabeth Dietze  Gerhard Kuhn  Oliver Esper  Ines Voigt  Kai Hartmann  Bernhard Diekmann 《Marine Geophysical Researches》2016,37(1):49-70

A multi-proxy study including sedimentological, mineralogical, biogeochemical and micropaleontological methods was conducted on sediment core PS69/849-2 retrieved from Burton Basin, MacRobertson Shelf, East Antarctica. The goal of this study was to depict the deglacial and Holocene environmental history of the MacRobertson Land–Prydz Bay region. A special focus was put on the timing of ice-sheet retreat and the variability of bottom-water formation due to sea ice formation through the Holocene. Results from site PS69/849-2 provide the first paleo-environmental record of Holocene variations in bottom-water production probably associated to the Cape Darnley polynya, which is the second largest polynya in the Antarctic. Methods included end-member modeling of laser-derived high-resolution grain size data to reconstruct the depositional regimes and bottom-water activity. The provenance of current-derived and ice-transported material was reconstructed using clay-mineral and heavy-mineral analysis. Conclusions on biogenic production were drawn by determination of biogenic opal and total organic carbon. It was found that the ice shelf front started to retreat from the site around 12.8 ka BP. This coincides with results from other records in Prydz Bay and suggests warming during the early Holocene optimum next to global sea level rise as the main trigger. Ice-rafted debris was then supplied to the site until 5.5 cal. ka BP, when Holocene global sea level rise stabilized and glacial isostatic rebound on MacRobertson Land commenced. Throughout the Holocene, three episodes of enhanced bottom-water activity probably due to elevated brine rejection in Cape Darnley polynya occured between 11.5 and 9 cal. ka BP, 5.6 and 4.5 cal. ka BP and since 1.5 cal. ka BP. These periods are related to shifts from warmer to cooler conditions at the end of Holocene warm periods, in particular the early Holocene optimum, the mid-Holocene warm period and at the beginning of the neoglacial. In contrast, between 7.7 and 6.7 cal. ka BP, brine rejection shut down, maybe owed to warm conditions and pronounced open-water intervals.  相似文献   

A geomorphological seabed classification for the Weddell Sea,Antarctica     

Kerstin Jerosch  Gerhard Kuhn  Ingo Krajnik  Frauke Katharina Scharf  Boris Dorschel 《Marine Geophysical Researches》2016,37(2):127-141

Sea floor morphology plays an important role in many scientific disciplines such as ecology, hydrology and sedimentology since geomorphic features can act as physical controls for e.g. species distribution, oceanographically flow-path estimations or sedimentation processes. In this study, we provide a terrain analysis of the Weddell Sea based on the 500 m × 500 m resolution bathymetry data provided by the mapping project IBCSO. Seventeen seabed classes are recognized at the sea floor based on a fine and broad scale Benthic Positioning Index calculation highlighting the diversity of the glacially carved shelf. Beside the morphology, slope, aspect, terrain rugosity and hillshade were calculated and supplied to the data archive PANGAEA. Applying zonal statistics to the geomorphic features identified unambiguously the shelf edge of the Weddell Sea with a width of 45–70 km and a mean depth of about 1200 m ranging from 270 m to 4300 m. A complex morphology of troughs, flat ridges, pinnacles, steep slopes, seamounts, outcrops, and narrow ridges, structures with approx. 5–7 km width, build an approx. 40–70 km long swath along the shelf edge. The study shows where scarps and depressions control the connection between shelf and abyssal and where high and low declination within the scarps e.g. occur. For evaluation purpose, 428 grain size samples were added to the seabed class map. The mean values of mud, sand and gravel of those samples falling into a single seabed class was calculated, respectively, and assigned to a sediment texture class according to a common sediment classification scheme.  相似文献