An algorithm to resolve γ-rays from charged cosmic rays with DAMPE     

Zun-Lei Xu  Kai-Kai Duan  Zhao-Qiang Shen  Shi-Jun Lei  Tie-Kuang Dong  Fabio Gargano  Simone Garrappa  Dong-Ya Guo  Wei Jiang  Xiang Li  Yun-Feng Liang  Mario Nicola Mazziotta  Maria Fernanda Munoz Salinas  Meng Su  Valerio Vagelli  Qiang Yuan  Chuan Yue  Jing-Jing Zang  Ya-Peng Zhang  Yun-Long Zhang  Stephan Zimmer 《天文和天体物理学研究(英文版)》2018,(3)

The DArk Matter Particle Explorer(DAMPE),also known as Wukong in China,which was launched on 2015 December 17,is a new high energy cosmic ray and γ-ray satellite-borne observatory.One of the main scientific goals of DAMPE is to observe Ge V-Te V high energy γ-rays with accurate energy,angular and time resolution,to indirectly search for dark matter particles and for the study of high energy astrophysics. Due to the comparatively higher fluxes of charged cosmic rays with respect to γ-rays,it is challenging to identify γ-rays with sufficiently high efficiency,minimizing the amount of charged cosmic ray contamination. In this work we present a method to identify γ-rays in DAMPE data based on Monte Carlo simulations,using the powerful electromagnetic/hadronic shower discrimination provided by the calorimeter and the veto detection of charged particles provided by the plastic scintillation detector. Monte Carlo simulations show that after this selection the number of electrons and protons that contaminate the selected γ-ray events at～10 Ge V amounts to less than 1% of the selected sample.Finally,we use flight data to verify the effectiveness of the method by highlighting known γ-ray sources in the sky and by reconstructing preliminary light curves of the Geminga pulsar.  相似文献   

Mineralogy and temperature of crater Haulani on Ceres          下载免费PDF全文

F. Tosi  F. G. Carrozzo  A. Raponi  M. C. De Sanctis  G. Thangjam  F. Zambon  M. Ciarniello  A. Nathues  M. T. Capria  E. Rognini  E. Ammannito  M. Hoffmann  K. Krohn  A. Longobardo  E. Palomba  C. M. Pieters  K. Stephan  C. A. Raymond  C. T. Russell 《Meteoritics & planetary science》2018,53(9):1902-1924

We investigate the region of crater Haulani on Ceres with an emphasis on mineralogy as inferred from data obtained by Dawn's Visible InfraRed mapping spectrometer (VIR), combined with multispectral image products from the Dawn Framing Camera (FC) so as to enable a clear correlation with specific geologic features. Haulani, which is one of the youngest craters on Ceres, exhibits a peculiar “blue” visible to near‐infrared spectral slope, and has distinct color properties as seen in multispectral composite images. In this paper, we investigate a number of spectral indices: reflectance; spectral slopes; abundance of Mg‐bearing and NH₄‐bearing phyllosilicates; nature and abundance of carbonates, which are diagnostic of the overall crater mineralogy; plus a temperature map that highlights the major thermal anomaly found on Ceres. In addition, for the first time we quantify the abundances of several spectral endmembers by using VIR data obtained at the highest pixel resolution (~0.1 km). The overall picture we get from all these evidences, in particular the abundance of Na‐ and hydrous Na‐carbonates at specific locations, confirms the young age of Haulani from a mineralogical viewpoint, and suggests that the dehydration of Na‐carbonates in the anhydrous form Na₂CO₃ may be still ongoing.  相似文献   

Northwest Africa 11024—A heated and dehydrated unique carbonaceous (CM) chondrite     

Samuel Ebert  Addi Bischoff  Dennis Harries  Sarah Lentfort  Jean‐Alix Barrat  Andreas Pack  Jrme Gattacceca  Robbin Visser  Peter Schmid‐Beurmann  Stephan Kimpel 《Meteoritics & planetary science》2019,54(2):328-356

Based on the high abundance of fine‐grained material and its dark appearance, NWA 11024 was recognized as a CM chondrite, which is also confirmed by oxygen isotope measurements. But contrary to known CM chondrites, the typical phases indicating aqueous alteration (e.g., phyllosilicates, carbonates) are missing. Using multiple analytical techniques, this study reveals the differences and similarities to known CM chondrites and will discuss the possibility that NWA 11024 is the first type 3 CM chondrite. During the investigation, two texturally apparent tochilinite–cronstedtite intergrowths were identified within two thin sections. However, the former phyllosilicates were recrystallized to Fe‐rich olivine during a heating event without changing the textural appearance. A peak temperature of 400–600 °C is estimated, which is not high enough to destroy or recrystallize calcite grains. Thus, calcites were never constituents of the mineral paragenesis. Another remarkable feature of NWA 11024 is the occurrence of unknown clot‐like inclusions (UCLIs) within fine‐grained rims, which are unique in this clarity. Their density and S concentration are significantly higher than of the surrounding fine‐grained rim and UCLIs can be seen as primary objects that were not formed by secondary alteration processes inside the rims. Similarities to chondritic and cometary interplanetary dust particles suggest an ice‐rich first‐generation planetesimal for their origin. In the earliest evolution, NWA 11024 experienced the lowest degree of aqueous alteration of all known CM chondrites and subsequently, a heating event dehydrated the sample. We suggest to classify the meteorite NWA 11024 as the first type 3 CM chondrite similar to the classification of CV3 chondrites (like Allende) that could also have lost their matrix phyllosilicates by thermal dehydration.  相似文献   

Sea level induced variations in clay mineral composition in the southwestern South China Sea over the past 17,000 yr     

Stephan Steinke  Till J.J. Hanebuth  Christoph Vogt  Karl Stattegger 《Marine Geology》2008,250(3-4):199-210

Variations in clay mineral composition of sediment cores from the margin and continental slope of the Sunda Shelf (southern South China Sea, SE Asia) covering the past 17,000 yr reflect changing influences of sediment sources together with clay mineral partitioning processes in shallow waters. We identify the deglacial sea level rise as the principal factor driving these changes. During the late glacial, high values of kaolinite are interpreted to reflect a higher contribution of clays from soils that have formed on the exposed Sunda Shelf and in the southern archipelagos of Indonesia. At this time core sites were located in close proximity to the mouths of the Sunda Shelf palaeo-drainage systems on the emerged shelf (“Sundaland”). The progressive landward displacement of the coastline and breakdown of these vast drainage systems during deglaciation led to a decrease in influence of the kaolinite-rich southern sources. When the coastline had retreated closely to its present-day position in mid-Holocene times, the former dominance of southern sources was replaced by a stronger influence of illite-rich sources (e.g. Borneo). The overriding control of sea level changes on the clay mineral distribution patterns precludes a definite climatic interpretation of clay mineral data in terms of climatic/monsoonal changes in such highly dynamic sedimentary environment.  相似文献   

Late Quaternary solifluction sheets in the British uplands     

Stephan Harrison  Leanne Hughes  Neil Glasser  Oliver Kuras 《第四纪科学杂志》2021,36(7):1162-1173

Solifluction sheets are large-scale and extensive valley-floor and valley-side landforms developed widely in the British Isles from mass-wasting of glacial and periglacial sediments during late-glacial times. We describe their geographical distribution and review the processes that have led to their development. We use data from the Cheviot Hills, the one site in the British Isles where sedimentology and optically stimulated luminescence dating have been combined, to assess their age and nature of deposition. We also present data from central Wales where a new mapping and resistivity survey has reconstructed the nature of valley-side solifluction sheets. We explore the relative lack of recent research on these landforms and argue that solifluction sheets represent a clear example of how upland geomorphological systems have responded to late-glacial climate change. We end by identifying a number of areas where research on these enigmatic features could be focussed, including better understanding of their distribution, sedimentology and age.  相似文献   

The pre-weichselian glaciations of North-West Europe     

Jürgen Ehlers  Klaus-Dieter Meyer  Hans-Jürgen Stephan 《Quaternary Science Reviews》1984,3(1):1-40

In North-West Europe no evidence has been found for glaciations older than the Elsterian. The Elsterian seems to consist of at least two separate ice advances with a minor interval in between. During the Elsterian in the area south of the Baltic Sea over 400 m deep channels were cut into the underlying substratum by a combination of glacial erosion and meltwater activity. The channels were active until the Late Elsterian and were subsequently filled with meltwater deposits and glaciolacustrine silt and clay. During the Saalian no comparative channels were being formed. Three different ice advances can be distinguished within the Saalian, the stratigraphical correlation of which is to be discussed. No convincing evidence was found for any interglacial within the Saalian sequence. There are good reasons to assume that the ice advances were only separated from each other by minor ice-free intervals.  相似文献   

40Ar-39Ar Ages of Types 3 and 4, L and H Chondrites from Antarctica     

Thomas Stephan  Elmar K. Jessberger 《Meteoritics & planetary science》1988,23(4):373-377

Abstract— This is a report on ⁴⁰Ar-³⁹Ar studies of 7 low petrographic type L and H chondrites from Antarctica. From petrographic similarities it has been argued that the L3 chondrites ALHA77015, ?77167, ?77249, and ?77260 are pieces from a common fall (McKinley et al., 1981). Our results now confirm this supposition: The four meteorites have identical characteristic Ar-degassing patterns, very similar K, Ca, Cl, and ³⁶Ar_trapped contents, and similar ⁴⁰Ar-³⁹Ar ages of <4 Ga which are rather unusual for ordinary chondrites and might be due to shock. The undulating age patterns could be due to weathering or to ³⁹Ar recoil. The L4 chondrite ALHA77230 shows no age plateau and only a lower limit for the time of a severe degassing, 4.0 Ga, can be given. ALHA77226 and RKPA78002, two H4 chondrites, exhibit reasonably well defined age plateaus at about 4.3 and 4.4 Ga. Two individual chondrules from RKPA78002 have the same age as the whole rock sample.  相似文献   

The provenance of Australian uranium ore concentrates by elemental and isotopic analysis     

Elizabeth Keegan  Stephan Richter  Ian Kelly  Henri Wong  Patricia Gadd  Heinz Kuehn  Adolfo Alonso-Munoz 《Applied Geochemistry》2008

Elemental and isotopic ratio analyses of U ore concentrate samples, from the 3 operating U mining facilities in Australia, were carried out to determine if significant variations exist between their products, thereby allowing the U ore concentrate’s origin to be identified. Elemental analyses were conducted using inductively coupled plasma mass spectrometry (ICP-MS) and X-ray fluorescence spectrometry (XRF). Lead isotope ratios were measured using ICP-MS and U isotope analyses were conducted using thermal ionisation mass spectrometry (TIMS). Minute quantities of sample, such as that obtained from a swipe, were also examined for elemental concentrations using secondary ion mass spectrometry (SIMS). The results of multivariate statistical analysis show clear patterns in the trace elemental composition of the processed U ores, indicating that it is possible to use this feature as a unique identifier of an Australian U ore concentrate’s source. Secondary ion mass spectrometry analyses also allow individual particles to be differentiated using this ‘fingerprinting’ technique. Isotope ratios determined using TIMS reveal that there is a significant difference in the n(²³⁴U)/n(²³⁸U) isotope ratio between the U ore concentrate from each mine.  相似文献   

Changes of cloud microphysical properties during the transition from supercooled to mixed-phase conditions during CIME     

Stephan Mertes  Alfons Schwarzenbck  Paolo Laj  Wolfram Wobrock  Jean-Marc Pichon  Giordano Orsi  Jost Heintzenberg 《Atmospheric Research》2001,58(4)

A ground-based seeding experiment using carbon dioxide and propane sprayed from pressurized bottles was carried out under supercooled cloud conditions on a small spatial and short time scale. Water vapor deposition on the artificially generated dry ice and propane ice germs as the main ice formation process (nucleation and growth) is consistent with the experimental results. After nucleation, diffusional growth of the ice particles, partly at the expense of evaporating small droplets, was identified during the mixing of the seeding line with the ambient supercooled cloud. Within the seeding plume, ice water contents up to 80% of the total condensed water are observed, although the size of the formed ice particles did not exceed 25 μm. From the changes of the ice and supercooled liquid phase with time under mixed-phase conditions, liquid water content (LWC) evaporation, ice water content (IWC) formation, and ice crystal growth rates are estimated, which are not affected by the artificial nucleation process. Thus, these rates are assessed to be applicable for a growing ice phase of small ice particles in a young mixed-phase cloud, where other growth mechanisms, like riming or aggregation, are negligible.  相似文献   

Analyzing Outcrop-Scale Fracture Features to Supplement Investigations of Bedrock Aquifers     

Stephan B. Mabee  Kenneth C. Hardcastle 《Hydrogeology Journal》1997,5(4):21-36

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