Tree-ring analysis elucidating palaeo-environmental effects captured in an in situ fossil forest – The last 80 years within an early Permian ecosystem

© 2017 Elsevier B.V. The early Permian Chemnitz Fossil L agerstätte (Leukersdorf Formation, Chemnitz Basin, SE Germany) represents a diverse T 0 assemblage of a fossil forest ecosystem around the Sakmarian-Artinskian transition (290.6 ± 1.8 Ma), which was preserved by pyroclastic deposits of a multi-phased volcanic eruption. The multi-aged plant community consists of predominantly hygrophilous elements, which grew on an alluvial plain mineral substrate under sub-humid conditions, representing a wet spot environment. Strong seasonality triggered the formation of annual tree rings in arborescent woody plants, such as pycnoxylic gymnosperms, medullosan seed ferns and calamitaleans. From several hundred fossil trees, the 53 best-preserved specimens were selected and investigated in detail by measuring 2,081 tree rings in individual sequences of up to 77 rings. Ring sequences were analysed by standard dendrochronological methods to determine both annual growth rates and mean sensitivity. Morphological and statistical analyses on single tree rings reveal different tree-ring types according to the different plant groups. Pycnoxylic gymnosperms have distinct and regular tree rings, whereas medullosan seed ferns and calamitaleans show indistinct and regular tree rings as well as so called event rings. Results reveal differences between plant groups regarding their physiological reactions or adaptations to seasonal fluctuations. In comparison to pycnoxylic gymnosperms, both medullosan seed ferns and calamitaleans exhibit reduced growth rates and more sensitive reaction to environmental perturbances as water deficiency pointing to comparably lower adaptation to seasonally dry palaeoclimate. In this context, event rings are in many cases traced back to plant physiological stress during particularly severe drought periods. Altogether, these fossil trees serve as sensitive environmental archives, which shed light on growth conditions several decades back in time from the entombing eruption

Palaeoclimatic and site-specific conditions in the early Permian fossil forest of Chemnitz-Sedimentological, geochemical and palaeobotanical evidence

© 2015 Elsevier B.V. As significant indicators of deep-time palaeoclimate, a number of new palaeontological, pedological and geochemical characteristics are provided for the Chemnitz Fossil Lagerstätte to depict more precisely its environmental conditions. For the first time, several lines of evidence indicate that this fossil forest, instantaneously preserved by volcanic deposits, once received an annual precipitation of around 800-1100 mm, but grew on a nearly unweathered palaeosol. Although the composition of this rich and diverse T0 assemblage suggests a hygrophilous, dense and multi-aged vegetation dominated by conservative lineages, the habitat was affected by environmental disturbances and pronounced seasonality. Repeated changes in local moisture availability are suggested by geochemical proxies, the co-occurrence to intergrowth of calcic and ferric glaebules in the palaeosol and developmental traits of perennial vegetational elements. Specific substrate adaptation is reflected by different root systems and cyclic growth interruptions recorded in the stems, branches and roots of long-lived woody plants. Many differentially adapted terrestrial animals complete the more comprehensive reconstruction of a late Sakmarian ecosystem and its climatic and preservational controls. Albeit spatially confined, this diverse in-situ record may contribute to understand wetland-dryland dynamics of sub-tropical Northern Hemisphere Pangaea

UV and X-Ray Monitoring of AG Draconis During the 1994/1995 Outbursts

The recent 1994-1995 active phase of AG Draconis has given us for the first time the opportunity to follow the full X-ray behaviour of a symbiotic star during two successive outbursts and to compare with its quiescence X-ray emission. With \ros observations we have discovered a remarkable decrease of the X-ray flux during both optical maxima, followed by a gradual recovering to the pre-outburst flux. In the UV the events were characterized by a large increase of the emission line and continuum fluxes, comparable to the behaviour of AG Dra during the 1980-81 active phase. The anticorrelation of X-ray/UV flux and optical brightness evolution is shown to very likely be due to a temperature decrease of the hot component. Such a temperature decrease could be produced by an increased mass transfer to the burning compact object, causing it to slowly expand to about twice its original size.Comment: 12 pages postscript incl. figures, Proc. of Workshop on Supersoft X-Ray Sources, to appear in Lecture Notes in Physics vol. 472 (1996

Properties and nature of Be stars: 27. Orbital and recent long-term variations of the Pleiades Be star Pleione = BU Tauri

Radial-velocity variations of the H-alpha emission measured on the steep wings of the H-alpha line, prewhitened for the long-time changes, vary periodically with a period of (218.025 +/- 0.022)d, confirming the suspected binary nature of the bright Be star Pleione, a member of the Pleiades cluster. The orbit seems to have a high eccentricity over 0.7, but we also briefly discuss the possibility that the true orbit is circular and that the eccentricity is spurious owing to the phase-dependent effects of the circumstellar matter. The projected angular separation of the spectroscopic orbit is large enough to allow the detection of the binary with large optical interferometers, provided the magnitude difference primary - secondary is not too large. Since our data cover the onset of a new shell phase up to development of a metallic shell spectrum, we also briefly discuss the recent long-term changes. We confirm the formation of a new envelope, coexisting with the previous one, at the onset of the new shell phase. We find that the full width at half maximum of the H-alpha profile has been decreasing with time for both envelopes. In this connection, we briefly discuss Hirata's hypothesis of precessing gaseous disk and possible alternative scenarios of the observed long-term changes

Survival Rate, Fracture Strength and Failure Mode of Ceramic Implant Abutments After Chewing Simulation

The aim of this study was to compare titanium-reinforced ZrO2 and pure Al2O3 abutments regarding their outcome after chewing simulation and static loading. Forty-eight standard diameter implants with an external hexagon were divided into three groups of 16 implants each and restored with three different types of abutments (group A: ZrO2 abutments with titanium inserts; group B: densely sintered high-purity Al2O3 abutments; group C: titanium abutments). All abutments were fixated on the implants with gold-alloy screws at 32 Ncm torque, and metal crowns were adhesively cemented onto the abutments. The specimens were exposed to 1.2 million cycles in a chewing simulator. Surviving specimens were subsequently loaded until fracture in a static testing device. Fracture loads (N) and fracture modes were recorded. A Wilcoxon Rank test to compare fracture loads among the 3 groups and a Fisher exact test to detect group differences in fracture modes were used for statistical evaluation (

The randomized shortened dental arch study (RaSDA): design and protocol

<p>Abstract</p> <p>Background</p> <p>Various treatment options for the prosthetic treatment of jaws where all molars are lost are under discussion. Besides the placement of implants, two main treatment types can be distinguished: replacement of the missing molars with removable dental prostheses and non-replacement of the molars, i.e. preservation of the shortened dental arch. Evidence is lacking regarding the long-term outcome and the clinical performance of these approaches. High treatment costs and the long time required for the treatment impede respective clinical trials.</p> <p>Methods/design</p> <p>This 14-center randomized controlled investigator-initiated trial is ongoing. Last patient out will be in 2010. Patients over 35 years of age with all molars missing in one jaw and with at least both canines and one premolar left on each side were eligible. One group received a treatment with removable dental prostheses for molar replacement (treatment A). The other group received a treatment limited to the replacement of all missing anterior and premolar teeth using fixed bridges (treatment B). A pilot trial with 32 patients was carried out. Two hundred and fifteen patients were enrolled in the main trial where 109 patients were randomized for treatment A and 106 for treatment B. The primary outcome measure is further tooth loss during the 5-year follow-up. The secondary outcome measures encompassed clinical, technical and subjective variables. The study is funded by the Deutsche Forschungsgemeinschaft (German Research Foundation, DFG WA 831/2-1, 2-2, 2-3, 2-4, 2-5).</p> <p>Discussion</p> <p>The particular value of this trial is the adaptation of common design components to the very specific features of complex dental prosthetic treatments. The pilot trial proved to be indispensable because it led to a number of adjustments in the study protocol that considerably improved the practicability. The expected results are of high clinical relevance and will show the efficacy of two common treatment approaches in terms of oral health. An array of secondary outcome measures will deliver valuable supplementary information. If the results can be implemented in the clinical practice, the daily dental care should strongly profit thereof.</p> <p>Trial registration</p> <p>The trial is registered at ClinicalTrials.gov under ISRCTN68590603 (pilot trial) and ISRCTN97265367 (main trial).</p

The role of ATP and adenosine in the brain under normoxic and ischemic conditions

By taking advantage of some recently synthesized compounds that are able to block ecto-ATPase activity, we demonstrated that adenosine triphosphate (ATP) in the hippocampus exerts an inhibitory action independent of its degradation to adenosine. In addition, tonic activation of P2 receptors contributes to the normally recorded excitatory neurotransmission. The role of P2 receptors becomes critical during ischemia when extracellular ATP concentrations increase. Under such conditions, P2 antagonism is protective. Although ATP exerts a detrimental role under ischemia, it also exerts a trophic role in terms of cell division and differentiation. We recently reported that ATP is spontaneously released from human mesenchymal stem cells (hMSCs) in culture. Moreover, it decreases hMSC proliferation rate at early stages of culture. Increased hMSC differentiation could account for an ATP-induced decrease in cell proliferation. ATP as a homeostatic regulator might exert a different effect on cell trophism according to the rate of its efflux and receptor expression during the cell life cycle. During ischemia, adenosine formed by intracellular ATP escapes from cells through the equilibrative transporter. The protective role of adenosine A1 receptors during ischemia is well accepted. However, the use of selective A1 agonists is hampered by unwanted peripheral effects, thus attention has been focused on A2A and A3 receptors. The protective effects of A2A antagonists in brain ischemia may be largely due to reduced glutamate outflow from neurones and glial cells. Reduced activation of p38 mitogen-activated protein kinases that are involved in neuronal death through transcriptional mechanisms may also contribute to protection by A2A antagonism. Evidence that A3 receptor antagonism may be protective after ischemia is also reported

Naturschutz-Handeln im Klimawandel - Risikoabschätzungen und adaptives Management in Brandenburg

Der Schutz aller natürlichen biotischen und abiotischen Güter und Ressourcen ist unerlässlicher Bestandteil einer nachhaltigen Entwicklung in Brandenburg. In Wahrnehmung dieser gesellschaftlichen Querschnittsaufgabe müssen Naturschützer mit anthropogenen und natürlichen Veränderungen sowie deren Wechselwirkungen umgehen. Der Klimawandel beeinflusst zusehends die Funktionstüchtigkeit der biologischen Vielfalt. Er hat das Potenzial, die bisherigen Gefährdungen der Arten und Ökosysteme deutlich zu verstärken. Welche Optionen gibt es für ein klimawandelangepasstes Naturschutz-Handeln? Ausgewählte Antworten auf diese Frage gibt der vorliegende Band. Er stellt zwei neu entwickelte Instrumente für angepasste Planungsverfahren vor: eine Methode der standortbezogenen Risikoabschätzung zur Priorisierung von Handlungsräumen und -schwerpunkten, sowie MARISCO - eine Methode zur Anwendung eines adaptiven Risiko-Managements. Beide Ansätze wurden im Rahmen des Projektes mit Praxispartner erprobt. Nach einer 2012 erschienenen Analyse strategischer Grundlagen ist dies der zweite Band einer dreiteiligen Serie zur regionalen Anpassung des Naturschutzmanagements an den Klimawandel