Evolutionary synthesis modelling of young star clusters in merging galaxies     

Peter Anders  Uta Fritze-von Alvensleben  Richard de Grijs 《Astrophysics and Space Science》2003,284(2):937-940

The observational properties of globular cluster systems (GCSs) are vital tools to investigate the violent star formation histories of their host galaxies. This violence is thought to have been triggered by galaxy interactions or mergers. The most basic properties of a GCS are its luminosity function (number of clusters per luminosity bin) and color distributions. A large number of observed GCS show bimodal color distributions, which can be translated into a bimodality in either metallicity and/or age. An additional uncertainty comes into play when one considers extinction. These effects can be disentangled either by obtaining spectroscopic data for the clusters or by imaging observations in at least four passbands. This allows us then to discriminate between various formation scenarios of GCSs, e.g. the merger scenario by Ashman and Zepf, and the multi-phase collapse model by Forbes et al. Young and metal-rich star cluster populations are seen to form in interacting and merging galaxies. We analyse multiwavelength broad-band observations of these young cluster systems provided by the ASTROVIRTEL project. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

A comparative study of peat proxies from two eastern central Swedish bogs and their relation to meteorological data     

Anders Borgmark  Kristian Schoning 《第四纪科学杂志》2006,21(2):109-114

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The condensation origin of zoned metal grains in Queen Alexandra Range 94411: Implications for the formation of the Bencubbin‐like chondrites     

Mikhail I. PETAEV  Anders MEIBOM  Alexander N. KROT  John A. WOOD  Klaus KEIL 《Meteoritics & planetary science》2001,36(1):93-106

Abstract— Thermodynamic analysis of the compositional profiles across large chemically‐zoned Fe, Ni metal grains in the Bencubbin‐like chondrite Queen Alexandra Range (QUE) 94411 suggests that these grains formed by non‐equilibrium gas‐solid condensation under variable oxidizing conditions, isolation degree, and Cr depletion factors. The oxidizing conditions must have resulted from the complete vaporization of nebular regions with enhanced dust/gas ratios (～ 10–40 × solar). Because the origin of each of the metal grains studied requires different condensation parameters (dust/gas ratio, isolation degree, and Cr depletion factor), a high degree of heterogeneity in the formation region of the Bencubbin‐like chondrite metal is required. To preserve compositional zoning of the metal grains and prevent their melting and sulfidization, the grains must have been removed from the hot condensation region into cold regions where the accretion of the Bencubbin‐like asteroidal body took place.  相似文献   

Interferometric space missions for the search for terrestrial exoplanets: Requirements on the rejection ratio     

Lisa Kaltenegger  Malcolm Fridlund  Anders Karlsson 《Astrophysics and Space Science》2006,306(3):147-158

The requirements on space missions designed to study Terrestrial exoplanets are discussed. We then investigate whether the design of such a mission, specifically the Darwin nulling interferometer, can be carried out in a simplified scenario. The key element here is accepting somewhat higher levels of stellar leakage. We establish detailed requirements resulting from the scientific rationale for the mission, and calculate detailed parameters for the stellar suppression required to achieve those requirements. We do this utilizing the Darwin input catalogue. The dominating noise source for most targets in this sample is essentially constant for all targets, while the leakage diminishes with the square of the distance. This means that the stellar leakage has an effect on the integration time only for the nearby stars, while for the more distant targets its influence decreases significantly. We assess the impact of different array configurations and nulling profiles and identify the stars for which the detection efficiency can be maximized.  相似文献   

CITATION ON THE AWARD OF THE LEONARD MEDAL OF THE METEORITICAL SOCIETY     

Edward Anders 《Meteoritics & planetary science》1974,9(4):425-426

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Mobility and Transport of Nd Isotopes in the Vadose Zone During Weathering of Granitic Till in a Boreal Forest     

Björn Öhlander  Magnus Land  Johan Ingri  Anders Widerlund 《Aquatic Geochemistry》2014,20(1):1-17

There is a broad correlation between the ε_Nd values for rivers (including both the water and the particulate material it carries) and the age of the source terrain. This paper presents Nd isotope distribution data for soil, soil water, groundwater, and stream water samples gathered in a small catchment in northern Sweden. The results show that the release of Nd and Sm from boreal forests into streams and, eventually, into the oceans is more complicated than previously realized. The weathering of till causes changes in both the Nd isotopic composition and Sm/Nd ratios. Both the Sm/Nd ratio and ε_Nd were higher in strongly weathered soils horizons than in less weathered till, since minerals with high Sm/Nd ratios were, on average, more resistant to weathering than those with low Sm/Nd ratios. In contrast to the situation for the main minerals and the major elements, the weathering of rare earth elements (REE) was not restricted to the E-horizon: the measured REE concentrations continued to increase with depth in the C-horizon. In addition, REE released by weathering in the upper parts of the soil profile were partly secondarily retained at deeper levels. Therefore, the dissolved Nd released by weathering in the upper soil horizons was trapped and did not enter the groundwater directly. Rather, the Nd in the groundwater largely originated from weathering within the groundwater zone. However, this was not the only source of Nd in the stream water. The Nd isotope composition and Sm/Nd ratio were determined by the mixing between of Nd and Sm in the groundwater and REE-carrying organic material washed out of the soil profile. The groundwater close to the stream reaches the upper soil horizons during high discharge events such as snowmelts, and organic matter carrying Nd and Sm is washed out of the soils and thus released into the stream. Therefore, the Nd exported from catchment is derived from both the weathering within the groundwater zone, and the organic matter washed out from the soil. If longer timescales with more advanced weathering stages in the groundwater zone are considered, it cannot be ruled out that there will be a shift towards more radiogenic values in the exported Nd. Recorded shifts in the Nd isotopic composition in the ocean may thus not only reflect changed source regions, but also the weathering history of the same source region.  相似文献   

基于多期DEM和滑坡强度的滑坡风险评估     

薛强  张茂省  孙萍萍  程秀娟  Anders Solheim  Trond Magne Vernang 《地质通报》2013,32(6):925-934

滑坡危险性定量评估是滑坡风险评估中的关键和难点,也是当前国际风险管理研究中的热点问题.以滑坡密集分布的黑方台南塬为研究区,以32处典型滑坡为研究对象,依据多期三维数字高程模型(DEM),提出了一种基于强度的滑坡危险性定量评估技术方法.根据多期三维地形信息的解译及野外调查,编制多期滑坡分布图,计算滑坡活动的频率.利用GIS技术,利用滑坡体积与速度的乘积计算滑坡强度.将滑坡危险性定义为滑坡频率和滑坡强度的乘积,同时调查和分析了黑方台地区各类承灾体的类型、价值及其在相应滑坡强度下的易损性,在此基础上开展了单体滑坡风险评估和黑方台南塬滑坡风险区划.  相似文献   

Energy coefficients for a propeller series     

Anders Smrup Olsen 《Ocean Engineering》2004,31(3-4):401-416

The efficiency for a propeller is calculated by energy coefficients. These coefficients are related to four types of losses, i.e. the axial, the rotational, the frictional, and the finite blade number loss, and one gain, i.e. the axial gain. The energy coefficients are derived by use of the potential theory with the propeller modelled as an actuator disk. The efficiency based on the energy coefficients is calculated for a propeller series. The results show a good agreement between the efficiency based on the energy coefficients and the efficiency obtained by a vortex-lattice method.  相似文献   

Planetesimal Formation Through Streaming and Gravitational Instabilities     

Anders Johansen  Hubert Klahr 《Earth, Moon, and Planets》2011,108(1):39-43

Planets form in circumstellar discs as dust grains collide together and form ever larger bodies. However a major bottleneck occurs for bodies with sizes around a few centimetres or larger. These rocks and boulders have very poor sticking properties and spiral into the star in a few hundred years due to friction with the slower rotating gas. A possible way to overcome this “meter-barrier” is to have local concentrations of rocks and boulders that become gravitationally unstable and contract to form planetesimals of several kilometers in size. We present the results of numerical simulations of the coupled motion of gas and rocks in protoplanetary disc mid-planes. The gas rotates slightly sub-Keplerian due to the global, radial pressure gradient of the disc, causing a net velocity difference between the gas and the solids. This relative motion is in turn unstable to streaming instabilities, and the saturated state of the turbulence is characterised by dense particle clumps that are fed by the radial drift of isolated rocks. For realistic protoplanetary disc parameters the clumps are gravitationally unstable and contract on the time-scale of a few orbits to form bodies of several hundred kilometers in size. Magnetic fields may further augment the particle concentrations due to relatively long-lived high pressure bumps that form in magnetorotational turbulence. However, magnetic fields are not crucial to the gravoturbulent formation of planetesimals, rather magnetised turbulence allows collapse to occur for flows that are on the average less affected by the particles, i.e. for lower particle column densities.  相似文献   

CLustre: semi‐automated lineament clustering for palaeo‐glacial reconstruction          下载免费PDF全文

Mike J. Smith  Niels S. Anders  Saskia D. Keesstra 《地球表面变化过程与地形》2016,41(3):364-377

Datasets containing large numbers (>10 000) of glacial lineaments are increasingly being mapped from remotely sensed data in order to develop a palaeo‐glacial reconstruction or ‘inversion’. The palimpsest landscape presents a complex record of past ice flow and deconstructing this information into a logical history is an involved task. One stage in this process requires the identification of sets of genetically linked lineaments that can form the basis of a reconstruction. This paper presents a semi‐automated algorithm, CLustre, for lineament clustering that uses a locally adaptive, region growing, methodology. After outlining the algorithm, it is tested on synthetic datasets that simulate parallel and orthogonal cross‐cutting lineaments, encompassing 1500 separate classifications. Results show robust classification in most scenarios, although parallel overlap of lineaments can cause false positive classification unless there are differences in lineament length. Case studies for Dubawnt Lake and Victoria Island, Canada, are presented and compared with existing datasets. For Dubawnt Lake 9 out of 14 classifications directly match incorporating 89% of lineaments. For Victoria Island 57 out of 58 classifications directly match incorporating 95% of lineaments. Differences are related to small numbers of unclassified lineaments and parallel cross‐cutting lineaments that are of a similar length. CLustre enables the automated, repeatable, assignment of lineaments to flow sets using defined user criteria. This is important as qualitative visual interpretation may introduce bias, potentially weakening the testability of palaeo‐glacial reconstructions. In addition, once classified, summary statistics of lineament clusters can be calculated and subsequently used during the reconstruction process. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献