Abstract
Modern theories of quantum magnetism predict exotic multipolar states in weakly interacting strongly frustrated spin-1/2 Heisenberg chains with ferromagnetic nearest neighbor (NN) inchain ...exchange in high magnetic fields. Experimentally these states remained elusive so far. Here we report strong indications of a magnetic field-induced nematic liquid arising above a field of ~13 T in the edge-sharing chain cuprate LiSbCuO
4
≡ LiCuSbO
4
. This interpretation is based on the observation of a field induced spin-gap in the measurements of the
7
Li NMR spin relaxation rate
T
1
−1
as well as a contrasting field-dependent power-law behavior of
T
1
−1
vs.
T
and is further supported by static magnetization and ESR data. An underlying theoretical microscopic approach favoring a nematic scenario is based essentially on the NN XYZ exchange anisotropy within a model for frustrated spin-1/2 chains and is investigated by the DMRG technique. The employed exchange parameters are justified qualitatively by electronic structure calculations for LiCuSbO
4
.
New stable carbon and oxygen isotope data from an Upper Cretaceous section in Tibet are presented, and compared to carbon isotope records from England, Italy, and Germany. Together with a ...stratigraphic re-interpretation of published carbon isotope data from a nearby section in Tibet, our data can surprisingly well be correlated with the European sections. This indicates that, similar to the distinct positive carbon isotope excursion at the Cenomanian-Turonian boundary, also the broad positive carbon isotope shift in the middle-late Coniacian and early Santonian reflects a major perturbation of the carbon cycle on a global scale, even though organic-rich sediments related to the OAE3 appear to be mainly restricted to the Atlantic Ocean and adjacent basins. The data further show that, apart from the broad Coniacian-Santonian carbon isotope excursion, also isotopic shifts on a smaller scale in the Turonian and Coniacian, such as the Round Down, Pewsey, and Hitchwood Events, can be correlated over both hemispheres. This demonstrates that the development of global oceanic anoxic conditions and associated burial of large amounts of organic carbon do not constitute a prerequisite for globally reflected carbon isotopic shifts. The data from Tibet support the concept of a relation between main carbon isotope excursions and major sea-level variations. Cyclic fluctuations of geochemical and lithological parameters are likely to be orbitally driven. These cycles appear to be preferably reflected in the sediments during periods of lower or variable sea-level, whereas the ocean-atmosphere system seems to have operated in a different mode during long phases of high, stable sea-level, as during the Coniacian-Santonian OAE3.
The tyrosine kinase receptor Tie2 (also known as Tek) plays an important role in the development of the embryonic vasculature and persists in adult endothelial cells (ECs). Tie2 was shown to be ...upregulated in tumors and skin wounds, and its ligands angiopoietin-1 and -2, although they are not directly mitogenic, modulate neovascularization. To gain further insight into the regulation of Tie2, we have studied the effect of hypoxia and inflammatory cytokines, two conditions frequently associated with neoangiogenic processes, on Tie2 expression in human ECs. Exposure to 1% O(2) led to a time-dependent significant rise of Tie2 protein levels in human coronary microvascular endothelial cells (HCMECs) and dermal microvascular ECs (HMEC-1) (3.2- and 2.5-fold within 24 hours), which was reversible after reoxygenation, and induced a less marked increase in human umbilical vein ECs (HUVECs; 1.7-fold). Hypoxia-conditioned medium and D-deoxyglucose did not change Tie2 expression, but desferrioxamine and cobalt, which are known to mimic hypoxia-sensing mechanisms, induced Tie2 at ambient oxygen tensions. Tumor necrosis factor-alpha induced Tie2 in a time- and dose-dependent fashion in all 3 EC types (HUVEC, 2.3-fold; HMEC-1, 2. 8-fold; and HCMEC, 3.0-fold; 10 ng/mL, 24 hours). Enhanced expression was also found after exposure to interleukin-1beta (1 ng/mL). Changes in Tie2 protein levels were paralleled by changes in mRNA expression. In accordance with these in vitro findings, immunohistochemistry revealed focal upregulation of Tie2 in capillaries at the border of infarcted human and rat myocardium. In conclusion, the data show that hypoxia and inflammatory cytokines upregulate Tie2, which may contribute to the angiogenic response in ischemic tissues.
Middle–Late Miocene marine incursions are known from several foreland basin systems adjacent to the Andes, likely a result of combined foreland basin loading and sea-level rising. The equivalent ...formation in the southern Bolivian Chaco foreland Basin is the Middle–Late Miocene (14–7
Ma) Yecua Formation. New lithological and paleontological data permit a reconstruction of the facies and depositional environment. These data suggest a coastal setting with humid to semiarid floodplains, shorelines, and tidal and restricted shallow marine environments. The marine facies diminishes to the south and west, suggesting a connection to the Amazon Basin. However, a connection to the Paranense Sea via the Paraguayan Chaco Basin is also possible.
This paper presents the first detailed biostratigraphic analysis of the uppermost Santonian through uppermost Maastrichtian hemipelagic carbonate successions of south-east Spain based mainly on the ...stratigraphic distributions of planktic foraminifera. For the time interval studied, seven biozones of planktic foraminifera have been recognized. From oldest to youngest these are: the uppermost part of the
Dicarinella asymetrica Zone, and the
Globotruncanita elevata,
Globotruncana ventricosa,
Globotruncanita calcarata,
Globotruncana falsostuarti,
Gansserina gansseri and
Abathomphalus mayaroensis zones. The biostratigraphic succession obtained from the sections studied in the Prebetic area is compared with those from sections in Tercis (France) and Kalaat Senan (Tunisia).
Hypoxia‐inducible factor (HIF)‐1α and ‐2α are key regulators of the transcriptional response to hypoxia and pivotal in mediating the consequences of many disease states. In the present work, we ...define their temporo‐spatial accumulation after myocardial infarction and systemic hypoxia. Rats were exposed to hypoxia or underwent coronary artery ligation. Immunohistochemistry was used for detection of HIF‐1α and ‐2α proteins and target genes, and mRNA levels were determined by RNase protection. Marked nuclear accumulation of HIF‐1α and ‐2α occurred after both systemic hypoxia and coronary ligation in cardiomyocytes as well as interstitial and endothelial cells (EC) without pronounced changes in HIF mRNA levels. While systemic hypoxia led to widespread induction of HIF, expression after coronary occlusion occurred primarily at the border of infarcted tissue. This expression persisted for 4 wk, included infiltrating macrophages, and colocalized with target gene expression. Subsets of cells simultaneously expressed both HIF‐α subunits, but EC more frequently induced HIF‐2α. A progressive increase of HIF‐2α but not HIF‐1α occurred in areas remote from the infarct, including the interventricular septum. Cardiomyocytes and cardiac stromal cells exhibit a marked potential for a prolonged transcriptional response to ischemia mediated by HIF. The induction of HIF‐1α and ‐2α appears to be complementary rather than solely redundant.
A middle to upper Cenomanian chalk succession in the northwestern European Paris Basin (Escalles section) was investigated with respect to its sediment composition, biofacies, and foraminiferal ...content. Most planktic foraminifers exhibit a high-frequency cyclicity in their distribution pattern and show little relationship to the sequence stratigraphic subdivision. A few characteristic species of benthic foraminifers (
Tritaxia pyramidata,
Ataxophragmium compactum,
Dorothia levis, and
Gavelinella cenomana) are related in their frequency distribution to certain systems tracts. Other benthic foraminiferal species are more evenly distributed through the systems tracts. Cluster analysis and factor analysis allow the separation of three benthic foraminiferal biofacies domains, which exhibit a characteristic frequency distribution pattern with respect to sequence stratigraphy. Biofacies 1 is dominant in the highstand systems tract (HST), and biofacies 3 is characteristic for the transgressive systems tract (TST). Biofacies 2 is most abundant around the maximum flooding–downlap surface (mfs) and less abundant around the sequence boundary. Factor analysis shows that most of the variance in the data set is explained by variables related to plankton productivity. Variables related to changes in water depth and changes in sea-level have minor influence on the variance of the whole data set, but have some influence on the variance of the benthic foraminiferal data set. The different reaction of benthic and planktic foraminifers to relative sea-level changes is also recorded in the total number of foraminifers per gram sediment (foraminiferal number) and in the ratio between planktic and benthic foraminifers (p/b-ratio). The foraminiferal number is highest at the mfs and lowest at the sequence boundaries of the investigated depositional sequences. The p/b-ratio has no correlation with the sequence stratigraphic subdivision, but shows a high-frequency cyclicity. The abundance pattern of planktic foraminifers is controlled by changes in the productivity of calcareous plankton. The regular variation in calcareous plankton productivity leads to marl (low productivity)–chalk (high productivity) cycles that form conspicuous couplets in the section. The productivity cycles are also recorded in gamma-ray logs in the environmental setting of the Escalles section. In contrast, the abundance patterns of benthic foraminifers are more influenced by relative sea-level changes, changes in water depth, and variations in substrate composition. The stacking of probably precession-controlled development of couplets lead to a distinct 100,000-year cyclicity that does not match very well with published sequence stratigraphic subdivisions.
Mid-Cenomanian, precession-controlled (21 ka) chalk–marl couplets of the Cap Blanc Nez section (Anglo–Paris Basin) have been studied with focus on the effects which Milankovitch cycles have had on ...the palaeoenvironment. In this paper, we present micropalaeontological and lithological proxies that enable the reconstruction of both the cycle architecture and the transformation of the orbitally forced signal into the sediment. A palaeoecological reconstruction based on changes in calcareous dinoflagellate cysts (c-dinocysts) assemblages was carried out, in which two characteristic ecological assemblages of c-dinocysts were identified. Gradual changes in absolute and relative abundance of the cyst species in these assemblages over several couplets depict a bundling pattern which is interpreted to reflect the modulation of the intensity of the precession cycle by the eccentricity cycle (100 ka). The stacking pattern in the natural gamma ray signal and the carbonate and TOC content has the same period and provides lithological support of the bundling. A shelf basin circulation model is proposed to explain the relation between orbitally forced climate change, its palaeoenvironmental consequences and the resulting sedimentary cyclicity. Variations in surface water circulation are reflected in the sediment by the chalk–marl couplets, the most distinctive couplets ocurring at the base and top of the bundles. While the chalks reflect well-mixed surface water conditions, the marls, particularly those at the bundle boundaries, can be interpreted as the sedimentary expression of stratified water masses. During deposition of these marls, reduced oceanic mixing due to low seasonality during strong precession maxima at the eccentricity maxima caused periods of water column stratification that in turn led to nutrient depletion and decreased productivity in the surface water masses.
The diversity record of abyssal agglutinated foraminifera reveals specific intervals during the past 150 million years when the diversity of species and ecological partitioning was high, interspersed ...by periods of lower diversity. We distinguish herein three faunas recovered from abyssal red claystones that represent periods of widespread oligotrophic conditions with low rates of sea-floor organic carbon flux. These are termed: the Tithonian to Barremian "Argo Fauna", the Turonian—Maastrichtian "Krashenninikov fauna", and the Eocene to early Oligocene "Iberia-Celebes Fauna". A fourth fauna (the mid-Cretaceous "Hatteras Fauna" and the "fiiofacies B Faunas") is observed during intervals characterised by eutrophic conditions that result in high organic flux and poorly oxygenated conditions at the sea floor.The taxonomic composition, diversity, and microhabitat preferences of agglutinated foraminiferal faunas in Cretaceous to Cainozoic deep sea sediments are related to a combination of environmental factors, including depth of the calcite compensation depth, ventilation of the bottom waters, and the amount of sea floor organic flux. These environmental conditions have changed in different ocean basins at different times and consequently the paleobiogeographical patterns of "Deep water agglutinated foraminifera" (DWAF) reflect general circulation patterns and resulting trophic conditions.We believe that the ecological structuring of agglutinated foraminifera within habitats may have been one of the most important driving forces in the evolution of this group. We conclude that the diversification of distinctive abyssal assemblages at specific times in ocean history depends upon the establishment of oligotrophic conditions in the deep sea following perturbations to the trophic structure caused by periods of increased organic carbon flux. Our comparison of Cretaceous to Recent DWAF reveals that evolutionary changes mainly took place among forms adapted to the oligotrophic end of the trophic resource continuum (i.e. passive deposit feeders, suspension feeders and some infaunal forms), whereas stasis prevailed among species adapted to eutrophic conditions (active epifaunal and shallow infaunal deposit feeders such as ammodiscids). Although the Neogene record of DWAF faunas is very poor, we observe that the modem sub-CCD fauna of the oligotrophic abyssal plains had its origins in the abyssal faunas of the Cretaceous and Paleogene. / Die Diversitätsentwicklung abyssaler agglutinierender Foraminiferen zeigt während der letzten 150 Millionen Jahre charakteristische, die von Perioden niedriger Diversität unterbrochen werden. Wir unterscheiden drei Faunen aus abyssalem roten Tiefseeton, die Perioden mit weitverbreitet oligotrophen Bedingungen und dementsprechend niedrigen Flußraten organischen Kohlenstoffs zum Meeresboden repräsentieren. Diese Faunen werden hier als "Argo Fauna" (Tithon-Barreme), "Krashenninikov-Fauna" (Turon—Maastricht) und "Iberia-Celebes-Fauna" (Eozänbasales Oligozän) bezeichnet. Eine vierte Fauna (die mittelkretazische "Hatteras-Fauna" und "Biofazies B"-Faunen) tritt nut während Zeitabschnitten mit eutrophen Bedingungen und entsprechend hohem Kohlenstofffluß und niedrigem Sauerstoffgehalt am Meeresboden auf.Die Artenzusammensetzung, Diversitäten und bevorzugten Lebensräume agglutierender Foraminiferenfaunen in kretazischen und känozoischen Tiefseesedimenten hangen von einer Kombination von Umweltfaktoren ab, zu denen die Lage der Kalzit-Kompensationstiefe (CCD), die Ventilation des Tiefenwassers und die Flußraten organischen Kohlenstoffs zum Meeresboden gehören. Diese Umweltbedingungen änderten sich rnehrfach in den verschiedenen Ozeanbecken und dementsprechend spiegeln paläobiogeographische Verteilungsmuster benthischer Foraminiferen generelle Zirkulationsmuster und daraus resultierende trophische Bedingungen wider.Wir gehen davon aus, daß die ökologische Struktur agglutinierender Foraminiferenfaunen in ihrem Lebensraum eine der wichtigsten treibenden Kräfte in der Evolution dieser Gruppe war. Daraus schließen wir, daß die zu bestimmten Zeiten beobachtete Diversifizierung abyssaler Faunengemeinsehaften an die Entstehung oligotropher Bedingungen nach Störungen des trophischen Gleichgewichts durch Phasen ungewöhnlich hohem Kohlenstoffflusses gebunden ist. Ein VergIeich kretazischer und rezenter Tiefseeforaminiferen-Gemeinschaften zeigt, daß evolutionare Veränderungen vor allem solche Formen betrafen, die an das oligotrophe Ende des trophisehen Ressourcen-Kontinuums angepaßt sind (z.B. passive Detritusfresser, Suspensionsfresser und einige endobenthische Formen). Dagegen herrscht bei Formen Stasis vor, die an eutrophe Bedingungen angepaßt sind (aktive epibenthisehe und flach endohenthische Detritusfresser wie etwa Ammodisciden). Obwohl immer noch relativ wenig über neogene agglutinierende Tiefwasser-Foraminiferen bekannt ist, lassen unsere Beobachtungen darauf sehließen, daß die moderne Sub-CCD Fauna der oligotrophen Tiefseeebenen ihren Ursprung in den abyssalen Faunen der Kreide und des Paläogen hatte.
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