Preliminary assessment of the ATHENA/WFI non-X-ray background     

Emanuele Perinati  Marco Barbera  Sebastian Diebold  Alejandro Guzman  Andrea Santangelo  Chris Tenzer 《Experimental Astronomy》2017,44(3):387-399

We present a preliminary assessment of the non-X-ray background for the WFI on board ATHENA conducted at IAAT in the context of the collaborative background and radiation damage working group activities. Our main result is that in the baseline configuration originally assumed for the camera the requirement on the level of non-X-ray background could not be met. In light of the results of Geant4 simulations we propose and discuss a possible optimization of the camera design and pinpoint some open issues to be addressed in the next phase of investigation. One of these concerns the possible contribution to the non-X-ray background from soft protons and ions funneled to the focal plane through the optics. This is not quantified at this stage, here we just briefly report on our ongoing activities aimed at validating the mechanisms of proton scattering at grazing incidence.  相似文献   

‘PALEOVAN’, International Continental Scientific Drilling Program (ICDP): site survey results and perspectives     

Thomas Litt  Sebastian Krastel  Michael Sturm  Rolf Kipfer  Sefer Örcen  Georg Heumann  Sven Oliver Franz  Umut B. Ülgen  Frank Niessen 《Quaternary Science Reviews》2009,28(15-16):1555-1567

Lake Van is the fourth largest terminal lake in the world (volume 607 km³, area 3570 km², maximum depth 460 m), extending for 130 km WSW–ENE on the Eastern Anatolian High Plateau, Turkey. The sedimentary record of Lake Van, partly laminated, has the potential to obtain a long and continuous continental sequence that covers several glacial–interglacial cycles (ca 500 kyr). Therefore, Lake Van is a key site within the International Continental Scientific Drilling Program (ICDP) for the investigation of the Quaternary climate evolution in the Near East (‘PALEOVAN’). As preparation for an ICDP drilling campaign, a site survey was carried out during the past years. We collected 50 seismic profiles with a total length of ～850 km to identify continuous undisturbed sedimentary sequences for potential ICDP locations. Based on the seismic results, we cored 10 different locations to water depths of up to 420 m. Multidisciplinary scientific work at positions of a proposed ICDP drill site included measurements of magnetic susceptibility, physical properties, stable isotopes, XRF scans, and pollen and spores. This core extends back to the Last Glacial Maximum (LGM), a more extended record than all the other Lake Van cores obtained to date. Both coring and seismic data do not show any indication that the deepest part of the lake (Tatvan Basin, Ahlat Ridge) was dry or almost dry during past times. These results show potential for obtaining a continuous undisturbed, long continental palaeoclimate record. In addition, this paper discusses the potential of ‘PALEOVAN’ to establish new results on the dynamics of lake level fluctuations, noble gas concentration in pore water of the lake sediment, history of volcanism and volcanic activities based on tephrostratigraphy, and paleoseismic and earthquake activities.  相似文献   

Relationship between the environmental and hydrogeological elements characterizing groundwater-dependent ecosystems in central Poland     

Ewa Krogulec  Sebastian Zabłocki 《Hydrogeology Journal》2015,23(7):1587-1602

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Shear behavior of DFDP-1 borehole samples from the Alpine Fault,New Zealand,under a wide range of experimental conditions     

Matt J. Ikari  Sebastian Trütner  Brett M. Carpenter  Achim J. Kopf 《International Journal of Earth Sciences》2015,104(6):1523-1535

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Late Holocene Asian summer monsoon dynamics from small but complex networks of paleoclimate data     

Kira Rehfeld  Norbert Marwan  Sebastian F. M. Breitenbach  Jürgen Kurths 《Climate Dynamics》2013,41(1):3-19

Internal variability of the Asian monsoon system and the relationship amongst its sub-systems, the Indian and East Asian Summer Monsoon, are not sufficiently understood to predict its responses to a future warming climate. Past environmental variability is recorded in Palaeoclimate proxy data. In the Asian monsoon domain many records are available, e.g. from stalagmites, tree-rings or sediment cores. They have to be interpreted in the context of each other, but visual comparison is insufficient. Heterogeneous growth rates lead to uneven temporal sampling. Therefore, computing correlation values is difficult because standard methods require co-eval observation times, and sampling-dependent bias effects may occur. Climate networks are tools to extract system dynamics from observed time series, and to investigate Earth system dynamics in a spatio-temporal context. We establish paleoclimate networks to compare paleoclimate records within a spatially extended domain. Our approach is based on adapted linear and nonlinear association measures that are more efficient than interpolation-based measures in the presence of inter-sampling time variability. Based on this new method we investigate Asian Summer Monsoon dynamics for the late Holocene, focusing on the Medieval Warm Period (MWP), the Little Ice Age (LIA), and the recent period of warming in East Asia. We find a strong Indian Summer Monsoon (ISM) influence on the East Asian Summer Monsoon during the MWP. During the cold LIA, the ISM circulation was weaker and did not extend as far east. The most recent period of warming yields network results that could indicate a currently ongoing transition phase towards a stronger ISM penetration into China. We find that we could not have come to these conclusions using visual comparison of the data and conclude that paleoclimate networks have great potential to study the variability of climate subsystems in space and time.  相似文献   

Projected climate change impact on Baltic Sea cyanobacteria     

Inga Hense  H. E. Markus Meier  Sebastian Sonntag 《Climatic change》2013,119(2):391-406

Compared to other phytoplankton groups, nitrogen-fixing cyanobacteria generally prefer high water temperatures for growth and are therefore expected to benefit from global warming. We use a coupled biological-physical model with an advanced cyanobacteria life cycle model to compare the abundance of cyanobacteria in the Baltic Sea during two different time periods (1969–1998; 2069–2098). For the latter, we find prolonged growth and a more than twofold increase in the climatologically (30 years) averaged cyanobacteria biomass and nitrogen fixation. Additional sensitivity experiments indicate that the biological-physical feedback mechanism through light absorption becomes more important with global warming. In general, we find a nonlinear response of cyanobacteria to changes in the atmospheric forcing fields as a result of life-cycle related feedback mechanisms. Overall, the sensitivity of the cyanobacteria-driven system suggests that biological-physical and life-cycle related feedback mechanisms are important and must therefore be included in future projection studies.  相似文献   

A global model study of natural bromine sources and the effects on tropospheric chemistry using MOZART4     

Gabriela Sousa Santos  Sebastian Rast 《Journal of Atmospheric Chemistry》2013,70(1):69-89

Halogens in the atmosphere chemically destroy ozone. In the troposphere, bromine has higher ozone destruction efficiency than chlorine and is the halogen species with the widest geographical spread of natural sources. We investigate the relative strength of various sources of reactive tropospheric bromine and the influence of bromine on tropospheric chemistry using a 6-year simulation with the global chemistry transport model MOZART4. We consider the following sources: short-lived bromocarbons (CHBr₃, CH₂BrCl, CHBr₂Cl, CHBrCl₂, and CH₂Br₂) and CH₃Br, bromine from airborne sea salt particles, and frost flowers and sea salt on or in the snowpack in polar regions. The total bromine emissions in our simulations add up to 31.7 Gmol(Br)/yr: 63 % from polar sources, 24.6 % from short-lived bromocarbons and 12.4 % from airborne sea salt particles. We conclude from our analysis that our global bromine emission is likely to be on the lower end of the range, because of too low emissions from airborne sea salt. Bromine chemistry has an effect on the oxidation capacity of the troposphere, not only due to its direct influence on ozone concentrations, but also by reactions with other key chemical species like HO _x and NO _x . Globally, the impact of bromine chemistry on tropospheric O₃ is comparable to the impact of gas-phase sulfur chemistry, since the inclusion of bromine chemistry in MOZART4 leads to a decrease of the O₃ burden in the troposphere by 6 Tg, while we get an increase by 5 Tg if gas-phase sulfur chemistry is switched off in the standard model. With decreased ozone burden, the simulated oxidizing capacity of the atmosphere decreases thus affecting species associated with the oxidation capacity of the atmosphere (CH₃OOH, H₂O₂).  相似文献   

A Fundamental Plane of Black Hole Activity: Pushing Forward the Unification Scheme     

Andrea Merloni  Sebastian Heinz  Tiziana Di Matteo 《Astrophysics and Space Science》2005,300(1-3):45-53

We examine the disc-jet connection in stellar mass and supermassive black holes by investigating the properties of their compact emission in the hard X-ray and radio bands. We compile a sample of ∼100 active galactic nuclei with measured mass, 5 GHz core emission, and 2–10 keV luminosity, together with eight galactic black holes with a total of ∼50 simultaneous observations in the radio and X-ray bands. Using this sample, we study the correlations between the radio (L_R) and the X-ray (L_X) luminosity and the black hole mass (M). We find that the radio luminosity is correlated with both M and L_X, at a highly significant level. We show how this result can be used to extend the standard unification by orientation scheme to encompass unification by mass and accretion rate.  相似文献   

A Fundamental Plane of black hole activity   总被引：1，自引：0，他引：1  

Andrea Merloni  Sebastian Heinz  Tiziana Di Matteo 《Monthly notices of the Royal Astronomical Society》2003,345(4):1057-1076

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Freshwater Ostracodes in Quaternary Permafrost Deposits in the Siberian Arctic     

Sebastian?WetterichEmail author  Lutz?Schirrmeister  Erika?Pietrzeniuk 《Journal of Paleolimnology》2005,34(3):363-376

Ostracode analysis was carried out on samples from ice-rich permafrost deposits obtained on the Bykovsky Peninsula (Laptev Sea). A composite profile was investigated that covers most of a 38-m thick permafrost sequence and corresponds to the last ca. 60 kyr of the Late Quaternary. The ostracode assemblages are similar to those known from European Quaternary lake deposits during cold stages. The ostracode habitats were small, shallow, cold, oligotrophic pools located in low centred ice wedge polygons or in small thermokarst depressions. In total, 15 taxa, representing 7 genera, were identified from 65 samples. The studied section is subdivided into six ostracode zones that correspond to Late Quaternary climatic and environmental stadial-interstadial variations established by other paleoenvironmental proxies: (1) cold and dry Zyrianian stadial (58–53 kyr BP); (2) warm and dry Karginian interstadial (48–34 kyr BP); (3) transition from the Karginian interstadial to the cold and dry Sartanian stadial (34–21 kyr BP); (4) transition from the Sartanian stadial to the warm and dry Late Pleistocene period, the Allerød (21–14 kyr BP); (5) transition from the Allerød to the warm and wet Middle Holocene (14–7 kyr BP); and (6) cool and wet Late Holocene (ca. 3 kyr BP). The abundance and diversity of the ostracodes will be used as an additional bioindicator for paleoenvironmental reconstructions of the Siberian Arctic.  相似文献