Accurate cosmic shear errors: do we need ensembles of simulations?

Accurate inference of cosmology from weak lensing shear requires an accurate shear power spectrum covariance matrix. Here, we investigate this accuracy requirement and quantify the relative importance of the Gaussian (G), super-sample covariance (SSC) and connected non-Gaussian (cNG) contributions to the covariance. Specifically, we forecast cosmological parameter constraints for future wide-field surveys and study how different covariance matrix components affect parameter bounds. Our main result is that the cNG term represents only a small and potentially negligible contribution to statistical parameter errors: the errors obtained using the G+SSC subset are within lesssim 5% of those obtained with the full G+SSC+cNG matrix for a Euclid-like survey. This result also holds for the shear two-point correlation function, variations in survey specifications and for different analytical prescriptions of the cNG term. The cNG term is that which is often tackled using numerically expensive ensembles of survey realizations. Our results suggest however that the accuracy of analytical or approximate numerical methods to compute the cNG term is likely to be sufficient for cosmic shear inference from the next generation of surveys

Experiences with an Online Mobile Learning Platform. Intervention for marginalised young people

Marginalised young people who find themselves disadvantaged in a number of respects also tend to experience limited access to Information and Communication Technologies (ICT) – with the exception of mobile phones. The European Commission-funded ComeIn project seeks to take advantage of marginalised young people’s access to mobile phones by reaching out to them via an innovative pedagogical approach based on the media convergence of the mobile phone through an online platform with video streaming. The platform was developed specifically for the purposes of the project to create the possibility for new, positive learning experiences as well as for interaction with peers and youth workers. In a three-month study in Austria and the United Kingdom, 94 young people accessed the platform via their mobile phones. In this paper we discuss the appropriateness of media convergence as a means for learning in and across three dimensions: interaction, creative expression and self-organisation. Furthermore, we explore how to incorporate initiatives such as ComeIn in an institutionalised context

Atmospheric influences on the anomalous 2016 Antarctic sea ice decay

In contrast to the Arctic, where total sea ice extent (SIE) has been decreasing for the last three decades, Antarctic SIE has shown a small, but significant, increase during the same time period. However, in 2016, an unusually early onset of the melt season was observed; the maximum Antarctic SIE was already reached as early as August rather than the end of September, and was followed by a rapid decrease. The decay was particularly strong in November, when Antarctic SIE exhibited a negative anomaly (compared to the 1979–2015 average) of approximately 2 million km2. ECMWF Interim reanalysis data showed that the early onset of the melt and the rapid decrease in sea ice area (SIA) and SIE were associated with atmospheric flow patterns related to a positive zonal wave number three (ZW3) index, i.e., synoptic situations leading to strong meridional flow and anomalously strong southward heat advection in the regions of strongest sea ice decline. A persistently positive ZW3 index from May to August suggests that SIE decrease was preconditioned by SIA decrease. In particular, in the first third of November northerly flow conditions in the Weddell Sea and the Western Pacific triggered accelerated sea ice decay, which was continued in the following weeks due to positive feedback effects, leading to the unusually low November SIE. In 2016, the monthly mean Southern Annular Mode (SAM) index reached its second lowest November value since the beginning of the satellite observations. A better spatial and temporal coverage of reliable ice thickness data is needed to assess the change in ice mass rather than ice area

The Potential Role of a Hydrogen Network in Europe

Electricity transmission expansion has suffered many delays in Europe in recent decades, despite its significance for integrating renewable electricity into the energy system. A hydrogen network which reuses the existing fossil gas network could not only help to supply demand for low-emission fuels, but could also to balance variations in wind and solar energy across the continent and thus avoid power grid expansion. We pursue this idea by varying the allowed expansion of electricity and hydrogen grids in net-zero CO2 scenarios for a sector-coupled and self-sufficient European energy system with high shares of renewables. We cover the electricity, buildings, transport, agriculture, and industry sectors across 181 regions and model every third hour of a year. With this high spatio-temporal resolution, the model can capture bottlenecks in transmission networks, the variability of demand and renewable supply, as well as regional opportunities for the retrofitting of legacy gas infrastructure and the development of geological hydrogen storage. Our results show consistent system cost reductions with a pan-continental hydrogen network that connects regions with low-cost and abundant renewable potentials to demand centres, synthetic fuel production and cavern storage sites. Developing a hydrogen network reduces system costs by up to 26 billion Euros per year (3.4%), with the highest benefits when electricity grid reinforcements cannot be realised. Between 64% and 69% of this network could be built from repurposed natural gas pipelines. However, we find that hydrogen networks can only partially substitute for power grid expansion. While the expansion of both networks together can achieve the largest cost savings of 10%, the expansion of neither is truly essential as long as higher costs can be accepted and regulatory changes are made to manage grid bottlenecks.Comment: including supplementary materia

Flow with the beat! Human-centered design of virtual environments for musical creativity support in VR

As previous studies have shown, the environment of creative people can have a significant impact on their creative process and thus on their creations. However, with the advent of digital tools such as virtual instruments and digital audio workstations, more and more creative work is digital and decoupled from the creator’s environment. Virtual Reality technologies open up new possibilities here, as creative tools can seamlessly merge with any virtual environment the user finds himself in. This paper reports on the human-centered design process of a VR application that aims at supporting the user’s individual needs to support their creativity while composing percussive beats in virtual environments. For this purpose, we derived factors that influence creativity from literature and conducted focus group interviews in order to learn how virtual environments and 3DUI can be designed for creativity support. In a subsequent laboratory study, we let users interact with a virtual step sequencer UI in virtual environments that were either customizable or fixed/unchangeable. By analyzing post-test ratings from music experts, self-report questionnaires, and user behavior data, we examined the effects of such customizable virtual environments on user creativity, user experience, flow, and subjective creativity support scales. While we did not observe a significant impact of this independent variable on user creativity, user experience or flow, we found that users had specific individual needs regarding their virtual surroundings and strongly preferred customizable virtual environments, even though the fixed virtual environment was designed to be creatively stimulating. We also observed consistently high flow and user experience ratings, which promote human-centered design of VR-based creativity support tools in a musical context

Enhanced spin-orbit coupling in core/shell nanowires

The spin-orbit coupling (SOC) in semiconductors is strongly influenced by structural asymmetries, as prominently observed in bulk crystal structures that lack inversion symmetry. Here, we study an additional effect on the SOC: the asymmetry induced by the large interface area between a nanowire core and its surrounding shell. Our experiments on purely wurtzite GaAs/AlGaAs core/shell nanowires demonstrate optical spin injection into a single free-standing nanowire and determine the effective electron g-factor of the hexagonal GaAs wurtzite phase. The spin relaxation is highly anisotropic in time-resolved micro-photoluminescence measurements on single nanowires, showing a significant increase of spin relaxation in external magnetic fields. This behavior is counterintuitive compared to bulk wurtzite crystals. We present a model for the observed electron spin dynamics highlighting the dominant role of the interface-induced SOC in these core/shell nanowires. This enhanced SOC may represent an interesting tuning parameter for the implementation of spin-orbitronic concepts in semiconductor-based structures

ProSeg: A comparative corpus of spoken L2 French

International audienc

Using boundary objects to make students brokers across disciplines: A dialogue between students and their lecturers on Bertolini’S node-place model

The competencies required for steering urban development sustainably are scattered amongst various disciplines. This is particularly relevant for planners working at the interface of different sub-disciplines, such as transport and land-use planning, exemplified by transit-oriented development (TOD). In this paper, we use Bertolini’s node-place model (NPM) example for TOD to test whether it enables interdisciplinary work to be undertaken in planning education. We tested our hypothesis in two design studios by challenging urban design students to develop their own design brief based on an NPM. The paper is of a dialogic, discursive nature. Students discuss whether or not the NPM enables them to better understand the relationship between transit and urban development and to develop spatial strategies based upon an integrative approach. Our discussion reveals that the NPM cannot necessarily bridge disciplinary boundaries successfully. However, both lecturers and students see value in the model as a didactic instrument