University of Cologne

About: University of Cologne is a education organization based out in Cologne, Germany. It is known for research contribution in the topics: Population & Gene. The organization has 32050 authors who have published 66350 publications receiving 2210092 citations. The organization is also known as: Universität zu Köln & Universitatis Coloniensis.

Poly‐Lactic‐Acid for coating of endovascular stents: preliminary results in canine experimental av‐fistulae

Abstract: Poly-Lactic-Acid (PLA) was evaluated for coating of vascular endoprostheses in the treatment of experimental arterio-venous-fistulae (AVF). Bilateral carotid – external jugular AVF were created in 5 adult dogs. 7 PLA coated nitinol stents were placed via a transfemoral approach covering 5 AVF. The contralateral AVF remained untreated. Angiography was performed immediately after stent placement, at weeks 1 and 3 and at months 3, 6 and 9. All grafts were removed and underwent histologic examination. In 2 cases the occlusion of the AVF was successful, while misplacement occurred in 3 cases. Occlusion of the parent vessel was disclosed in 3 cases. Histologic examination revealed a mild inflammatory reaction with the presence of macrophages. There was no foreign-body reaction or fragmentation of the arterial vessel wall. PLA, which is a well-known biodegradable material, showed a good mid-term biocompatibility. Elastic mismatch of the non-elastic coating and the self-expandable nitinol stent caused misplacement. Frequent vessel-occlusions were probably due to PLA-filaments fraying into the vessel lumen. Using a different textile structure PLA might be a material suitable for coating endovascular stents. Poly-Laktid zur Ummantelung von Gefasprothesen: erste tierexperimentelle Ergebnisse in der Behandlung arterio-venoser Gefaskurzschlusse In der vorliegenden Arbeit wurden mit Poly-Laktid ummantelte Gefasprothesen in der Behandlung von experimentell angelegten arterio-venosen Gefaskurzschlussen getestet. Gefaskurzschlussverbindungen der Halsarterien mit der parallel dazu verlaufenden, tiefen Halsvene wurden in 5 Hunden operativ angelegt. 7 mit Poly-Laktid ummantelte Gefasprothesen aus Nitinol wurden in jeweils eine Halsarterie implantiert, so dass die Gefaskurzschlussverbindung vollstandig uberdeckt war. Die gegenuberliegende Seite verblieb als Kontrolle unbehandelt. Radiologische Gefasdarstellungen erfolgten unmittelbar nach Implantation der Gefasprothese, nach 1 und 3 Wochen sowie nach 3, 6 und 9 Monaten. Alle Prothesen wurden operativ entfernt und feingeweblich untersucht. Ein erfolgreicher Verschluss der Kurzschlussverbindung gelang lediglich in 2 Fallen. In den 3 ubrigen Fallen kam es zu einer Fehlplatzierung der Gefasprothese. Gefasverschlusse der geschienten Arterien wurden in 3 Fallen beobachtet. Die feingewebliche Untersuchung zeigte geringe, entzundliche Zellreaktionen. Fremdkorperreaktionen bzw. Destruktionen der Gefaswand wurden nicht beobachtet. Mittelfristig zeigte Poly-Laktid, ein biologisch abbaubares Material, eine gute Biokompatibilitat. Das Missverhaltnis zwischen der nichtelastischen Poly-Laktid Ummantelung und der elastischen Gefasprothese erschwerte die zielgenaue, endovaskulare Platzierung. Wahrscheinlich verursachten die endstandigen Auffaserungen der Poly-Laktid-Ummantelung die haufigen Gefasverschlusse. Unter Verwendung anderer Webstrukturen konnte Poly-Laktid ein interessantes Material zur Ummantelung von Gefasprothesen sein.

Empirical fitness landscapes and the predictability of evolution

Abstract: A central topic in biology concerns how genotypes determine phenotypes and functions of organisms that affect their evolutionary fitness. This Review discusses recent advances in the development of empirical fitness landscapes and their contribution to theoretical analyses of the predictability of evolution. The genotype–fitness map (that is, the fitness landscape) is a key determinant of evolution, yet it has mostly been used as a superficial metaphor because we know little about its structure. This is now changing, as real fitness landscapes are being analysed by constructing genotypes with all possible combinations of small sets of mutations observed in phylogenies or in evolution experiments. In turn, these first glimpses of empirical fitness landscapes inspire theoretical analyses of the predictability of evolution. Here, we review these recent empirical and theoretical developments, identify methodological issues and organizing principles, and discuss possibilities to develop more realistic fitness landscape models.

Climate-Driven Ecosystem Succession in the Sahara: The Past 6000 Years

Abstract: Desiccation of the Sahara since the middle Holocene has eradicated all but a few natural archives recording its transition from a "green Sahara" to the present hyperarid desert. Our continuous 6000- year paleoenvironmental reconstruction from northern Chad shows progressive drying of the regional terrestrial ecosystem in response to weakening insolation forcing of the African monsoon and abrupt hydrological change in the local aquatic ecosystem controlled by site- specific thresholds. Strong reductions in tropical trees and then Sahelian grassland cover allowed large- scale dust mobilization from 4300 calendar years before the present ( cal yr B. P.). Today's desert ecosystem and regional wind regime were established around 2700 cal yr B. P. This gradual rather than abrupt termination of the African Humid Period in the eastern Sahara suggests a relatively weak biogeophysical feedback on climate.