The MOSAiC ice floe: Sediment-laden survivor from the Siberian shelf

In September 2019, the research icebreaker Polarstern started the largest multidisciplinary Arctic expedition to date, the MOSAiC (Multidisciplinary drifting Observatory for the Study of Arctic Climate) drift experiment. Being moored to an ice floe for a whole year, thus including the winter season, the declared goal of the expedition is to better understand and quantify relevant processes within the atmosphere-ice-ocean system that impact the sea ice mass and energy budget, ultimately leading to much improved climate models. Satellite observations, atmospheric reanalysis data, and readings from a nearby meteorological station indicate that the interplay of high ice export in late winter and exceptionally high air temperatures resulted in the longest ice-free summer period since reliable instrumental records began. We show, using a Lagrangian tracking tool and a thermodynamic sea ice model, that the MOSAiC floe carrying the Central Observatory (CO) formed in a polynya event north of the New Siberian Islands at the beginning of December 2018. The results further indicate that sea ice in the vicinity of the CO ( \u3c 40 km distance) was younger and 36 % thinner than the surrounding ice with potential consequences for ice dynamics and momentum and heat transfer between ocean and atmosphere. Sea ice surveys carried out on various reference floes in autumn 2019 verify this gradient in ice thickness, and sediments discovered in ice cores (so-called dirty sea ice) around the CO confirm contact with shallow waters in an early phase of growth, consistent with the tracking analysis. Since less and less ice from the Siberian shelves survives its first summer (Krumpen et al., 2019), the MOSAiC experiment provides the unique opportunity to study the role of sea ice as a transport medium for gases, macronutrients, iron, organic matter, sediments and pollutants from shelf areas to the central Arctic Ocean and beyond. Compared to data for the past 26 years, the sea ice encountered at the end of September 2019 can already be classified as exceptionally thin, and further predicted changes towards a seasonally ice-free ocean will likely cut off the long-range transport of ice-rafted materials by the Transpolar Drift in the future. A reduced long-range transport of sea ice would have strong implications for the redistribution of biogeochemical matter in the central Arctic Ocean, with consequences for the balance of climate-relevant trace gases, primary production and biodiversity in the Arctic Ocean

Erratum to: 36th International Symposium on Intensive Care and Emergency Medicine

[This corrects the article DOI: 10.1186/s13054-016-1208-6.]

Mud dynamics in the Port of Zeebrugge

This paper presents the mud dynamics in the harbor basin of Zeebrugge in the Southern North Sea based on an analysis of field data. Mud is typically transported into and within the harbor basin through advection of suspended particulate matter (SPM). Three important timescales have been identified. On the intratidal timescale, sediment import occurs from 2 h before high water to high water. Flood currents in the North Sea (directed northeastward along the Belgian coast) drive the primary gyre in the harbor mouth which is advected into the basin during rising tide. This results in water inflow near the eastern breakwater and outflow near the western breakwater. Because of sediment settling in the harbor, this results in a net import of SPM. During spring tide, the SPM flux into the harbor basin is two to four times higher than during neap tide. However, the volume of sediment removed from the port by maintenance dredging is kept constant over the spring-neap cycle, causing the amount of mud in the harbor basin to grow around spring tide conditions. On the seasonal timescale, mud volume within the harbor basin is larger in winter and reaches a minimum at the beginning of autumn. Moreover, the measured densities within the deposited mud layers are lower in winter than in summer. The most shallow point of the 210-kHz reflector is also more shallow in winter. Finally, the profile of the interface of the mud layer in the sheltered Albert II dock is more horizontal in winter than in summer, suggesting seasonal variations in the strength of the mud layer. The question to what degree the seasonal variation of thickness and density of the fluid mud layer is related to differences in the suspended sediment input, to differences in the settling rates of suspended flocs, or to the mud consolidation rate remains open however. The data do not show a strong influence of meteorological conditions (waves, freshwater inflow) on siltation rates in the harbor basin.Environmental Fluid Mechanic

Wall heat loads in a cryogenic rocket thrust chamber during thermoacoustic instabilities

A subscale, research rocket thrust chamber operating with cryogenic oxygen and hydrogen exhibits self-excited transverse-mode instabilities with amplitudes of more than 80% of the steady combustion chamber pressure (peak-to-peak) for some operating conditions. During unstable combustion, an increase in the integral heat flux into the water-cooled combustion chamber walls of 20–40% with respect to stable conditions was experienced. A model was derived to predict changes in the axial heat flux profile considering only the dependence of flame length on the amplitude of transverse acoustic oscillations. The model predicts an increase in heat flux in the upstream part of the chamber by up to a factor of 7. This drastic increase is in agreement with past observations of rocket engine failures due to instabilities, in which the structural damage is commonly observed on the faceplate and the walls adjacent to the injection plane. The model also predicts a peak increase in integral heat flux of up to about 25%. While falling short of the peak experimental value of 40%, it nevertheless suggests that flame length is the dominant influence on the distribution of thermal loads in this study.Space Systems Egineerin

Sponge City Project

The report starts in Chapter 1 with an introduction to the Sponge City Programme (SCP) in China and the project area which is the ErQi International Business District in Wuhan. In this chapter, the problem statement, our collaboration with Arcadis and our project goals are also introduced. Chapter 2 delves into our methodology to tackle the brief. Starting from how we shaped our interdisciplinary approach, we explain our approach towards the project and our decision to include resiliency with the Sponge City concept as an objective. We continue by providing background information on ErQi area in Chapter 3 to get an overall understanding of the planned urban design and potential urban flooding. To provide a thorough analysis and recommendations for the selection process of adaptation measures to mitigate excess rainfall as part of the SCP in the context of ErQi area, an assessment of the Wuhan Sponge City criteria, a stakeholder analysis complemented by a spatial assessment was performed and described in Chapter 4. Setting the context allows understanding the complexity of the system and its constraints in the implementation of the SCP. Thus, we decided to first focus on the implementation of low-impact development (LID) measures using a multi-criteria analysis (MCA) presented in Chapter 4 and then developed an integrated and resilient system design later in the report. As the Sponge City is not sufficient to cope with high precipitation events (Arcadis, 2017), the project combines sponge city and resiliency principles in an integrated system approach.The guiding resilient design principles of the Sponge City are further described and explained in Chapter 5 and applied in the opportunistic design process in Chapter 6, bridging the research with the designs. Here the designs of the MengQiao Bridge and the Water Road are presented along with their proposed effects on the urban flooding. Chapter 7 serves to assess the designs through the criteria of the integrated sponge city to improve flood resilience. The following chapter serves to share our conclusions on the challenges for implementing a functioning of the SCP that includes the concept of resilience. It also touches upon the difficulty of implementing the value-based design in a profit-based context. The final chapter is composed of five parts, all of which is our recommendations. It starts with our recommendations to improve the Sponge City criteria to make them more effective in reaching the goals of the programme. Then we give our recommendations for the selection process of LID followed by what we have learned of this interdisciplinary approach. That includes what we consider to be crucial to achieving a genuinely interdisciplinary process resulting in an integrated design. The final part of the chapter is dedicated to what we believe should be researched further. We believe a more in-depth assessment of the designs with the Sponge City criteria and input of the stakeholders is required for a final design. Further, the working definitions and approach of the Wuhan city government need to be considered, and an approach that assesses the necessary maintenance protocols is necessary.Multidisciplinary project reportMP260Water Managemen

Triplet correlations in Cooper pair splitters realized in a two-dimensional electron gas

Cooper pairs occupy the ground state of superconductors and are typically composed of maximally entangled electrons with opposite spin. In order to study the spin and entanglement properties of these electrons, one must separate them spatially via a process known as Cooper pair splitting (CPS). Here we provide the first demonstration of CPS in a semiconductor two-dimensional electron gas (2DEG). By coupling two quantum dots to a superconductor-semiconductor hybrid region we achieve efficient Cooper pair splitting, and clearly distinguish it from other local and non-local processes. When the spin degeneracy of the dots is lifted, they can be operated as spin-filters to obtain information about the spin of the electrons forming the Cooper pair. Not only do we observe a near perfect splitting of Cooper pairs into opposite-spin electrons (i.e. conventional singlet pairing), but also into equal-spin electrons, thus achieving triplet correlations between the quantum dots. Importantly, the exceptionally large spin-orbit interaction in our 2DEGs results in a strong triplet component, comparable in amplitude to the singlet pairing. The demonstration of CPS in a scalable and flexible platform provides a credible route to study on-chip entanglement and topological superconductivity in the form of artificial Kitaev chains.QRD/Goswami La

An Overview of the Conceptual Design Studies of Hybrid Electric Propulsion Air Vehicles in the Frame of Clean Sky 2 Large Passenger Aircraft

In the Clean Sky 2 Large Passenger Aircraft (LPA) program the potential of innovative hybrid electric propulsion (HEP) air vehicle concepts has been investigated by the projects ADEC (Advanced Engine and Aircraft Configuration) and NOVAIR (Novel Aircraft Configurations and Scaled Flight Testing Instrumentation). In a combined effort the members of the two projects worked closely together to identify promising technologies for air vehicle concepts that utilize hybrid electric powertrains. The vehicle design studies were divided onto the three distinct teams of DLR, TU Delft/NLR (NOVAIR), and ONERA. This paper will summarize the design efforts and the results obtained from the HEP design space exploration.Flight Performance and Propulsio

Lateral variation in slab window viscosity inferred from global navigation satellite system (GNSS)–observed uplift due to recent mass loss at Patagonia ice fields

The geographic coincidence of the Chile Ridge slab window and the Patagonia ice fields offers a unique opportunity for assessing the effects of slab window rheology on glacial isostatic adjustment (GIA). Mass loss of these ice fields since the Little Ice Age causes rapid but variable crustal uplift, 12–24 mm/yr around the North Patagonia ice field, increasing to a maximum of 41 mm/yr around the South Patagonia ice field, as determined from newly collected or processed geodetic data. We used these observational constraints in a three-dimensional Maxwell viscoelastic finite element model of GIA response above both the subducting slab and slab window in which the upper-mantle viscosity was parameterized to be uniform with depth. We found that the viscosity of the northern part of the slab window, ~2 × 1018 Pa·s, is lower than that of the southern part by approximately an order of magnitude. We propose that this along-strike viscosity contrast is due to late Cenozoic ridge subduction beneath the northern part of the slab window, which increases asthenospheric temperature and reduces viscosityGreen Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Astrodynamics & Space Mission