The effect of galaxy mass ratio on merger-driven starbursts     

T. J. Cox  Patrik Jonsson  Rachel S. Somerville  Joel R. Primack  Avishai Dekel 《Monthly notices of the Royal Astronomical Society》2008,384(1):386-409

We employ numerical simulations of galaxy mergers to explore the effect of galaxy mass ratio on merger-driven starbursts. Our numerical simulations include radiative cooling of gas, star formation, and stellar feedback to follow the interaction and merger of four disc galaxies. The galaxy models span a factor of 23 in total mass and are designed to be representative of typical galaxies in the local universe. We find that the merger-driven star formation is a strong function of merger mass ratio, with very little, if any, induced star formation for large mass ratio mergers. We define a burst efficiency that is useful to characterize the merger-driven star formation and test that it is insensitive to uncertainties in the feedback parametrization. In accord with previous work we find that the burst efficiency depends on the structure of the primary galaxy. In particular, the presence of a massive stellar bulge stabilizes the disc and suppresses merger-driven star formation for large mass ratio mergers. Direct, coplanar merging orbits produce the largest tidal disturbance and yield the most intense burst of star formation. Contrary to naive expectations, a more compact distribution of gas or an increased gas fraction both decrease the burst efficiency. Owing to the efficient feedback model and the newer version of smoothed particle hydrodynamics employed here, the burst efficiencies of the mergers presented here are smaller than in previous studies.  相似文献   

Pressure- and temperature-dependent thermal expansivity and the effect on mantle convection and surface observables     

Harro Schmeling  Gabriele Marquart  Thomas Ruedas 《Geophysical Journal International》2003,154(1):224-229

  相似文献   

A multi-dimensional assessment of urban vulnerability to climate change in Sub-Saharan Africa     

Herslund  Lise Byskov  Jalayer  Fatemeh  Jean-Baptiste  Nathalie  J&#;rgensen  Gertrud  Kabisch  Sigrun  Kombe  Wilbard  Lindley  Sarah  Nyed  Patrik Karlsson  Pauleit  Stephan  Printz  Andreas  Vedeld  Trond 《Natural Hazards》2015,82(2):149-172

In this paper, we develop and apply a multi-dimensional vulnerability assessment framework for understanding the impacts of climate change-induced hazards in Sub-Saharan African cities. The research was carried out within the European/African FP7 project CLimate change and Urban Vulnerability in Africa, which investigated climate change-induced risks, assessed vulnerability and proposed policy initiatives in five African cities. Dar es Salaam (Tanzania) was used as a main case with a particular focus on urban flooding. The multi-dimensional assessment covered the physical, institutional, attitudinal and asset factors influencing urban vulnerability. Multiple methods were applied to cover the full range of vulnerabilities and to identify potential response strategies, including: model-based forecasts, spatial analyses, document studies, interviews and stakeholder workshops. We demonstrate the potential of the approach to assessing several dimensions of vulnerability and illustrate the complexity of urban vulnerability at different scales: households (e.g., lacking assets); communities (e.g., situated in low-lying areas, lacking urban services and green areas); and entire cities (e.g., facing encroachment on green and flood-prone land). Scenario modeling suggests that vulnerability will continue to increase strongly due to the expected loss of agricultural land at the urban fringes and loss of green space within the city. However, weak institutional commitment and capacity limit the potential for strategic coordination and action. To better adapt to urban flooding and thereby reduce vulnerability and build resilience, we suggest working across dimensions and scales, integrating climate change issues in city-level plans and strategies and enabling local actions to initiate a ‘learning-by-doing’ process of adaptation.

  相似文献   

Winter colonisation and succession of filamentous macroalgae on artificial substrates and possible relationships to Fucus vesiculosus settlement in early summer     

Patrik Kraufvelin  Ari T. Ruuskanen  Niko Nappu  Mikko Kiirikki   《Estuarine, Coastal and Shelf Science》2007,72(4):665-674

During the reproduction period of Fucus vesiculosus, which occurs only once a year (in May–June) along the Finnish coast of the northern Baltic Sea, a thick carpet of filamentous algae often covers hard substrates suitable for zygote settlement. By placing out artificial substrates into the field, monthly over a period of eight months prior to F. vesiculosus settlement (October 2001–June 2002), we investigated the autumn/winter/spring colonisation and succession of filamentous algae and their possible relationships with the settlement success of F. vesiculosus under naturally variable field conditions. The substrates exposed in October 2001 became covered by filamentous brown algal Pilayella littoralis mats, which persisted over the settlement period of F. vesiculosus, but now also were accompanied by large amounts of the filamentous green alga Cladophora glomerata. The substrates exposed from November 2001 onwards hosted smaller amounts of P. littoralis during the winter and different filamentous algal communities at the time of F. vesiculosus settlement, i.e. less P. littoralis and C. glomerata, but Dictyosiphon foeniculaceus, Ceramium tenuicorne and Ulva intestinalis instead. We observed recruits of F. vesiculosus on all substrates, except on the ones placed out in October 2001. Significantly more P. littoralis and C. glomerata on the October substrates may explain the failed F. vesiculosus recruitment, although we could not establish direct causal or correlational relationships between filamentous algae and F. vesiculosus settlement. We compared the results with a previous un-replicated pilot study in the same area demonstrating similar response patterns.  相似文献   

Small-scale instabilities below the cooling oceanic lithosphere     

Gabriele Marquart  Harro Schmeling  & Alexander Braun 《Geophysical Journal International》1999,138(3):655-666

Interpretation of satellite altimetry data as well as ship bathymetry data revealed strongly elongated anomalies roughly perpendicular to the mid-ocean ridges in the Indian and east Pacific oceans. A spectral analysis of gravity altimetry data along profiles parallel to the East Pacific Rise indicated wavelengths of about 150–180  km close to the ridge and about 250  km further away. A simple model of Rayleigh–Taylor instabilities developing at the base of the cooling lithosphere is discussed and applied to the data. By considering thermal diffusion and comparing Rayleigh–Taylor growth rates to the velocity of the thermal front in the cooling lithosphere, we are able to explain the observed anomalies by instabilities developing below the lithosphere in a layer with a viscosity of about 10¹⁹  Pa  s above an asthenospheric layer with a viscosity reduction of 2–3 orders of magnitude.  相似文献   

Measuring accelerometer dynamic range from seismic data using Allan deviation          下载免费PDF全文

Matt McDonald  Patrik Stigborg 《Geophysical Prospecting》2018,66(5):934-941

We propose a new approach for calculating the dynamic range of an accelerometer based on an Allan deviation analysis of production seismic data. This test is intended as a field audit technique and does not require an unconditioned dataset from a low‐noise environment. We first show that Allan deviation can measure white noise levels using two commercial accelerometers. The analysis accurately captures the manufacturing noise density specifications and known relationships between white noise, preamplifier gain, and group forming. We then show that a production seismic dataset is suitable for an Allan deviation analysis because the results are not critically affected by a recording filter. Finally, we illustrate the proposed technique by calculating the dynamic range of an accelerometer channel in a seismic streamer using a production dataset.  相似文献   

Hydrogen suppresses UO₂ corrosion     

Paul Carbol  Patrik Fors  Kastriot Spahiu 《Geochimica et cosmochimica acta》2009,73(15):4366-4375

Release of long-lived radionuclides such as plutonium and caesium from spent nuclear fuel in deep geological repositories will depend mainly on the dissolution rate of the UO₂ fuel matrix. This dissolution rate will, in turn, depend on the redox conditions at the fuel surface. Under oxidative conditions UO₂ will be oxidised to the 1000 times more soluble UO_2.67. This may occur in a repository as the reducing deep groundwater becomes locally oxidative at the fuel surface under the effect of α-radiolysis, the process by which α-particles emitted from the fuel split water molecules. On the other hand, the groundwater corrodes canister iron generating large amounts of hydrogen. The role of molecular hydrogen as reductant in a deep bedrock repository is questioned. Here we show evidence of a surface-catalysed reaction, taking place in the H₂-UO₂-H₂O system where molecular hydrogen is able to reduce oxidants originating from α-radiolysis. In our experiment the UO₂ surface remained stoichiometric proving that the expected oxidation of UO_2.00 to UO_2.67 due to radiolytic oxidants was absent. As a consequence, the dissolution of UO₂ stopped when equilibrium was reached between the solid phase and U⁴⁺ species in the aqueous phase. The steady-state concentration of uranium in solution was determined to be 9 × 10⁻¹² M, about 30 times lower than previously reported for reducing conditions. Our findings show that fuel dissolution is suppressed by H₂. Consequently, radiotoxic nuclides in spent nuclear fuel will remain immobilised in the UO₂ matrix. A mechanism for the surface-catalysed reaction between molecular hydrogen and radiolytic oxidants is proposed.  相似文献   

Feedback in simulations of disc-galaxy major mergers     

T. J. Cox  Patrik Jonsson  Joel R. Primack  Rachel S. Somerville 《Monthly notices of the Royal Astronomical Society》2006,373(3):1013-1038

  相似文献   

Interpretations of geoid anomalies around the Iceland hotspot     

G. Marquart 《Geophysical Journal International》1991,106(1):149-160

  相似文献   

A benchmark comparison for mantle convection codes   总被引：2，自引：0，他引：2  

B. Blankenbach  F. Busse  U. Christensen  L. Cserepes  D. Gunkel  U. Hansen  H. Harder  G. Jarvis  M. Koch  G. Marquart  D. Moore  P. Olson  H. Schmeling  T. Schnaubelt 《Geophysical Journal International》1989,98(1):23-38

  相似文献