Ray Tracing Structured AMR Data Using ExaBricks

Structured Adaptive Mesh Refinement (Structured AMR) enables simulations to adapt the domain resolution to save computation and storage, and has become one of the dominant data representations used by scientific simulations; however, efficiently rendering such data remains a challenge. We present an efficient approach for volume- and iso-surface ray tracing of Structured AMR data on GPU-equipped workstations, using a combination of two different data structures. Together, these data structures allow a ray tracing based renderer to quickly determine which segments along the ray need to be integrated and at what frequency, while also providing quick access to all data values required for a smooth sample reconstruction kernel. Our method makes use of the RTX ray tracing hardware for surface rendering, ray marching, space skipping, and adaptive sampling; and allows for interactive changes to the transfer function and implicit iso-surfacing thresholds. We demonstrate that our method achieves high performance with little memory overhead, enabling interactive high quality rendering of complex AMR data sets on individual GPU workstations

Thin-disk laser-pumped OPCPA system delivering 4.4 TW few-cycle pulses

We present an optical parametric chirped pulse amplification (OPCPA) system delivering 4.4 TW pulses centered at 810 nm with a sub-9 fs duration and a carrier-envelope phase stability of 350 mrad. The OPCPA setup pumped by sub-10 ps pulses from two Yb:YAG thin-disk lasers at 100 Hz repetition rate is optimized for a high conversion-efficiency. The terawatt pulses of the OPCPA are utilized for generating intense extreme ultraviolet (XUV) pulses by high-order harmonic generation, achieving XUV pulse energies approaching the microjoule level. © 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreemen

Potential feedbacks between loss of biosphere integrity and climate change

Non-technical abstract Individual organisms on land and in the ocean sequester massive amounts of the carbon emitted into the atmosphere by humans. Yet the role of ecosystems as a whole in modulating this uptake of carbon is less clear. Here, we study several different mechanisms by which climate change and ecosystems could interact. We show that climate change could cause changes in ecosystems that reduce their capacity to take up carbon, further accelerating climate change. More research on – and better governance of – interactions between climate change and ecosystems is urgently required. Technical abstract Individual responses of terrestrial and marine species to future climate change will affect the capacity of the land and ocean to store carbon. How system-level changes in the integrity of the biosphere interact with climate change is more uncertain. Here, we explore the consequences of different hypotheses on the interactions between the climate–carbon system and the integrity of the terrestrial and marine biospheres. We investigate mechanisms including impairment of terrestrial ecosystem functioning due to lagged ecosystem responses, permafrost thaw, terrestrial biodiversity loss and impacts of changes in marine biodiversity on the marine biological pump. To investigate climate–biosphere interactions involving complex concepts such as biosphere integrity, we designed and implemented conceptual representations of these climate–biosphere interactions in a stylized climate–carbon model. We find that all four classes of interactions amplify climate change, potentially contributing up to an additional 0.4°C warming across all representative concentration pathway scenarios by the year 2100 and potentially turning the terrestrial biosphere into a net carbon source, although uncertainties are large. The results of this preliminary quantitative study call for more research on – and better integrated governance of – the interactions between climate change and biosphere integrity, the two core ‘planetary boundaries’.The research leading to these results has received funding from the Stordalen Foundation via the Planetary Boundary Research Network (PB.net), the Earth League’s EarthDoc programme, the Leibniz Association (project DOMINOES), European Research Council Synergy project Imbalance-P (grant ERC-2013-SyG-610028), European Research Council Advanced Investigator project ERA (grant ERC-2016-ADG-743080), Deutsche Forschungsgemeinschaft (DFG BE 6485/1-1), Project Grant 2014-589 from the Swedish Research Council Formas and a core grant to the Stockholm Resilience Centre by Mistra

Trajectories of the Earth System in the Anthropocene

This is the final version of the article. Available from National Academy of Sciences via the DOI in this record.We explore the risk that self-reinforcing feedbacks could push the Earth System toward a planetary threshold that, if crossed, could prevent stabilization of the climate at intermediate temperature rises and cause continued warming on a "Hothouse Earth" pathway even as human emissions are reduced. Crossing the threshold would lead to a much higher global average temperature than any interglacial in the past 1.2 million years and to sea levels significantly higher than at any time in the Holocene. We examine the evidence that such a threshold might exist and where it might be. If the threshold is crossed, the resulting trajectory would likely cause serious disruptions to ecosystems, society, and economies. Collective human action is required to steer the Earth System away from a potential threshold and stabilize it in a habitable interglacial-like state. Such action entails stewardship of the entire Earth System-biosphere, climate, and societies-and could include decarbonization of the global economy, enhancement of biosphere carbon sinks, behavioral changes, technological innovations, new governance arrangements, and transformed social values.W.S. and C.P.S. are members of the Anthropocene Working Group. W.S., J.R., K.R., S.E.C., J.F.D., I.F., S.J.L., R.W. and H.J.S. are members of the Planetary Boundaries Research Network PB.net and the Earth League’s EarthDoc Programme supported by the Stordalen Foundation. T.M.L. was supported by a Royal Society Wolfson Research Merit Award and the European Union Framework Programme 7 Project HELIX. C.F. was supported by the Erling– Persson Family Foundation. The participation of D.L. was supported by the Haury Program in Environment and Social Justice and National Science Foundation (USA) Decadal and Regional Climate Prediction using Earth System Models Grant 1243125. S.E.C. was supported in part by Swedish Research Council Formas Grant 2012-742. J.F.D. and R.W. were supported by Leibniz Association Project DOMINOES. S.J.L. receives funding from Formas Grant 2014-589. This paper is a contribution to European Research Council Advanced Grant 2016, Earth Resilience in the Anthropocene Project 743080

Pyrosequencing-Based Assessment of Bacterial Community Structure Along Different Management Types in German Forest and Grassland Soils

BACKGROUND: Soil bacteria are important drivers for nearly all biogeochemical cycles in terrestrial ecosystems and participate in most nutrient transformations in soil. In contrast to the importance of soil bacteria for ecosystem functioning, we understand little how different management types affect the soil bacterial community composition. METHODOLOGY/PRINCIPAL FINDINGS: We used pyrosequencing-based analysis of the V2-V3 16S rRNA gene region to identify changes in bacterial diversity and community structure in nine forest and nine grassland soils from the Schwäbische Alb that covered six different management types. The dataset comprised 598,962 sequences that were affiliated to the domain Bacteria. The number of classified sequences per sample ranged from 23,515 to 39,259. Bacterial diversity was more phylum rich in grassland soils than in forest soils. The dominant taxonomic groups across all samples (>1% of all sequences) were Acidobacteria, Alphaproteobacteria, Actinobacteria, Betaproteobacteria, Deltaproteobacteria, Gammaproteobacteria, and Firmicutes. Significant variations in relative abundances of bacterial phyla and proteobacterial classes, including Actinobacteria, Firmicutes, Verrucomicrobia, Cyanobacteria, Gemmatimonadetes and Alphaproteobacteria, between the land use types forest and grassland were observed. At the genus level, significant differences were also recorded for the dominant genera Phenylobacter, Bacillus, Kribbella, Streptomyces, Agromyces, and Defluviicoccus. In addition, soil bacterial community structure showed significant differences between beech and spruce forest soils. The relative abundances of bacterial groups at different taxonomic levels correlated with soil pH, but little or no relationships to management type and other soil properties were found. CONCLUSIONS/SIGNIFICANCE: Soil bacterial community composition and diversity of the six analyzed management types showed significant differences between the land use types grassland and forest. Furthermore, bacterial community structure was largely driven by tree species and soil pH