Over the last decade, our understanding of climate sensitivity has improved considerably. The climate system shows variability on many timescales, is subject to non-stationary forcing and it is most ...likely out of equilibrium with the changes in the radiative forcing. Slow and fast feedbacks complicate the interpretation of geological records as feedback strengths vary over time. In the geological past, the forcing timescales were different than at present, suggesting that the response may have behaved differently. Do these insights constrain the climate sensitivity relevant for the present day? In this paper, we review the progress made in theoretical understanding of climate sensitivity and on the estimation of climate sensitivity from proxy records. Particular focus lies on the background state dependence of feedback processes and on the impact of tipping points on the climate system. We suggest how to further use palaeo data to advance our understanding of the currently ongoing climate change.
This work presents a quantitative evaluation of polymer-based Capacitive Micromachined Ultrasonic Transducers (polyCMUTs) for 3D Ultrasound Computed Tomography (3D USCT). The study was motivated by ...limitations of the currently used PZT fiber technology in terms of bandwidth and transmit sensitivity. We developed finite element models of polyCMUT elements consisting of 127 cells to predict the acoustic performance. We fabricated prototype transducers using a novel method for microstructuring polymer layers. The produced samples reach a fractional bandwidth of 116%, an opening angle of 44° and increase the transmit sensitivity by 54%, compared to the PZT fiber transducers. The developed models allow for accurate predictions of the acoustic field over a large range of angles and frequencies. More work is required to improve the reliability and reduce sample-to-sample variations. Based on the measured performance and the general properties of the technology, polyCMUTs are very promising for 3D USCT.
Present-day (PD) and Last Glacial Maximum (LGM) simulations of the global ocean are presented, with the oxygen-18 isotope included as a passive tracer. The gradient of the PD North Atlantic surface δ
...18O:salinity relationship is found to result from different processes at low and high latitudes. At low latitudes, the balance between surface
18O flux and oceanic advection and mixing sets the surface δ
18O:salinity gradient, whereas at high latitudes, mixing between
18O-depleted runoff and precipitation to the Arctic, Bering Strait inflow, and waters from lower latitudes, controls the δ
18O:salinity gradient. The importance of the Bering Strait contribution has not previously been recognised. These gradients change significantly at the LGM, and are found to be sensitive to both Arctic runoff δ
18O concentrations and changes in oceanic advection, particularly the rate of exchange of North Atlantic deep water with the global ocean. It is concluded that reconstructions of past climates from records of sea surface δ
18O based on analogues of the PD δ
18O:salinity relationship are likely to be in error.
Zusammenfassung
Als metallfreies Pendant zu Titan haben sich Keramikimplantate auf Zirkoniumdioxidbasis in den vergangenen Jahren als charmante Alternative im zahnärztlichen Sektor ...herauskristallisiert. Vergleicht man die beiden Werkstoffe miteinander, korrelieren sie in puncto Biokompatibilität sowie Osseointegration exzellent miteinander. Dennoch machen keramische Implantate auf dem Weltmarkt nur etwa 5 % aller gefertigten Implantate aus. Viele Anwender stehen dem nichtmetallischen Material aufgrund angeblich mangelnder mechanischer Stabilität sowie eines schnelleren Alterungsverhaltens kritisch gegenüber. Doch sind diese Vorurteile gerechtfertigt und könnte der weltweite Anteil keramischer Implantate in den nächsten Jahren weiter steigen? Dieser Beitrag vergleicht neueste Studien und gibt einen Überblick der Vor- und Nachteile von Implantaten auf Zirkoniumdioxidbasis.
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