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Wyszukujesz frazę "Kiessling, W." wg kryterium: Autor


Wyświetlanie 1-3 z 3
Tytuł:
Using abundance data to assess the relative role of sampling biases and evolutionary radiations in Upper Muschelkalk ammonoids
Autorzy:
McGowan, A.J.
Kiessling, W.
Powiązania:
https://bibliotekanauki.pl/articles/22024.pdf
Data publikacji:
2013
Wydawca:
Polska Akademia Nauk. Instytut Paleobiologii PAN
Tematy:
Ammonoidea
Ceratites
biodiversity
rank abundance
paleoecology
Muschelkalk
Triassic
Upper Muschelkalk
ammonoid
Opis:
The Middle Triassic ammonoid genus Ceratites diversified spectacularly within the Germanic Muschelkalk Basin during the Anisian/Ladian (244–232 Mya). Previous studies have interpreted this diversification as a sequence of rapid, endemic radiations from a few immigrant taxa. Here we investigate the possibility that geological and sampling biases, rather than ecological and evolutionary processes, are responsible for this pattern. A new specimen−based dataset of Ceratites species−richness and abundance was assembled. This dataset was combined with 1:200 000 geological maps in a geodatabase to facilitate geospatial analyses. One set of analyses compared species richness per geological map with the number of occurrences and localities per map. Per−map change in the amount of rock available to sample for fossils was also included as a variable. Of these three variables, number of occurrences is the most strongly correlated with richness. Variation in the amount of rock is not a strong determinant of species−richness. However, rarefaction of basin−wide species/abundance data demonstrates that differences in species−richness through time are not attributable to sample size differences. The average percent similarity among sites remained close to 50% throughout the Upper Muschelkalk. The rank abundance distribution (RAD) of species from the first interval of the Upper Muschelkalk is consistent with colonization of a disturbed environment, while the other two intervals have RADs consistent with more stable ecosystems. These results indicate that genuine ecological and evolutionary events are partly responsible for the observed differences in richness and abundance. Although changes in the RADs through time support changes in the ammonoid assemblage structure, the processes underlying increasing richness and change in RADs cannot be explained by increasing geographic distinctiveness or isolation among the ammonoid assemblages present at different localities.
Źródło:
Acta Palaeontologica Polonica; 2013, 58, 3
0567-7920
Pojawia się w:
Acta Palaeontologica Polonica
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Biodiversity of museum and bulk field samples compared: The Eocene Chiampo sponge fauna, Lessini Mountains, Italy
Autorzy:
Frisone, V.
Pisera, A.
Preto, N.
Kiessling, W.
Powiązania:
https://bibliotekanauki.pl/articles/21824.pdf
Data publikacji:
2018
Wydawca:
Polska Akademia Nauk. Instytut Paleobiologii PAN
Opis:
The sponge body fossils from the Lutetian (Eocene) of Chiampo Valley in north-eastern Italy, Lessini Mountains, exhibit a high diversity. The fauna, comprising 32 species, was recently described in a systematic study based on museum material. Here we compare diversity measures and rank-abundance distributions between the museum material and new material from random surface collection at the original sampling site. Not surprisingly, we find that selectively collected museum material tends to have greater diversity and evenness than bulk field samples. Nevertheless, abundance rank - orders are maintained between samples. Bulk field sampling revealed hexactinellids to be strongly dominant over lithistids, which suggests a deep-water setting of greater than 200 m water depth.
Źródło:
Acta Palaeontologica Polonica; 2018, 63, 4
0567-7920
Pojawia się w:
Acta Palaeontologica Polonica
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
CdSe/ZnSe Quantum Dots Formed by Low Temperature Epitaxy and In-Situ Annealing: Properties and Growth Optimization
Autorzy:
Mahapatra, S.
Schumacher, C.
Kiessling, T.
Astakhov, G. V.
Bass, U.
Ossau, W.
Geurts, J.
Brunner, K.
Powiązania:
https://bibliotekanauki.pl/articles/2044500.pdf
Data publikacji:
2005-11
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
81.16.Dn
81.05.Dz
73.21.La
Opis:
The formation of CdSe/ZnSe quantum dots by a method combining a low temperature MBE growth of a CdSe layer and its subsequent in-situ annealing at temperatures between 280-340ºC has been studied. The thermal treatment results in a re-organization of the surface from a nearly two-dimensional layer to an ensemble of three-dimensional dot-like features. In this work we optimized the different growth and annealing parameters of this process and compared the properties of the resultant dots with those of dots grown by conventional MBE at 300ºC. It is demonstrated that the luminescence properties of the dots for both growth techniques are comparable but the areal density achieved by the in-situ annealing technique is an order of magnitude lower. From high resolution X-ray diffraction results, it could be established that no desorption takes place despite significantly long annealing duration. Beyond a nominal coverage of 3.5 ML CdSe, stacking faults are generated, leading to a gradual decrease in luminescence intensities and an overlap of pendellösung fringes in X-ray diffractograms.
Źródło:
Acta Physica Polonica A; 2005, 108, 5; 769-776
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
    Wyświetlanie 1-3 z 3

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