Heterogeneous nanofluids: natural convection heat transfer enhancement

Convective heat transfer using different nanofluid types is investigated. The domain is differentially heated and nanofluids are treated as heterogeneous mixtures with weak solutal diffusivity and possible Soret separation. Owing to the pronounced Soret effect of these materials in combination with a considerable solutal expansion, the resulting solutal buoyancy forces could be significant and interact with the initial thermal convection. A modified formulation taking into account the thermal conductivity, viscosity versus nanofluids type and concentration and the spatial heterogeneous concentration induced by the Soret effect is presented. The obtained results, by solving numerically the full governing equations, are found to be in good agreement with the developed solution based on the scale analysis approach. The resulting convective flows are found to be dependent on the local particle concentration φ and the corresponding solutal to thermal buoyancy ratio N. The induced nanofluid heterogeneity showed a significant heat transfer modification. The heat transfer in natural convection increases with nanoparticle concentration but remains less than the enhancement previously underlined in forced convection case

The EC-Earth3 Earth system model for the Coupled Model Intercomparison Project 6

The Earth system model EC-Earth3 for contributions to CMIP6 is documented here, with its flexible coupling framework, major model configurations, a methodology for ensuring the simulations are comparable across different high-performance computing (HPC) systems, and with the physical performance of base configurations over the historical period. The variety of possible configurations and sub-models reflects the broad interests in the EC-Earth community. EC-Earth3 key performance metrics demonstrate physical behavior and biases well within the frame known from recent CMIP models. With improved physical and dynamic features, new Earth system model (ESM) components, community tools, and largely improved physical performance compared to the CMIP5 version, EC-Earth3 represents a clear step forward for the only European community ESM. We demonstrate here that EC-Earth3 is suited for a range of tasks in CMIP6 and beyond

Lava field evolution and emplacement dynamics of the 2014–2015 basaltic fissure eruption at Holuhraun, Iceland

The 6-month long eruption at Holuhraun (August 2014–February 2015) in the Bárðarbunga-Veiðivötn volcanic system was the largest effusive eruption in Iceland since the 1783–1784 CE Laki eruption. The lava flow field covered ~84 km2 and has an estimated bulk (i.e., including vesicles) volume of ~1.44 km3. The eruption had an average discharge rate of ~90 m3/s making it the longest effusive eruption in modern times to sustain such high average flux. The first phase of the eruption (August 31, 2014 to mid-October 2014) had a discharge rate of ~350 to 100 m3/s and was typified by lava transport via open channels and the formation of four lava flows, no. 1–4,which were emplaced side by side. The eruption began on a 1.8 km long fissure, feeding partly incandescent sheets of slabby pāhoehoe up to 500 m wide. By the following day the lava transport got confined to open channels and the dominant lava morphology changed to rubbly pāhoehoe and ‘a’ā. The latter became the dominating morphology of lava flows no. 1–8. The second phase of the eruption (Mid-October to end November) had a discharge of ~100–50 m3/s. During this time the lava transport system changed, via the formation of a b1 km2 lava pond ~1 km east of the vent. The pond most likely formed in a topographical low created by a the pre-existing Holuhraun and the newHoluhraun lava flow fields. This pond became themain point of lava distribution, controlling the emplacement of subsequent flows (i.e. no. 5–8). Towards the end of this phase inflation plateaus developed in lava flowno. 1. These inflation plateaus were the surface manifestation of a growing lava tube system, which formed as lava ponded in the open lava channels creating sufficient lavastatic pressure in the fluid lava to lift the roof of the lava channels. This allowed new lava into the previously active lava channel lifting the channel roof via inflation. The final (third) phase, lasting from December to end-February 2015 had a mean discharge rate of ~50 m3/s. In this phase the lava transport was mainly confined to lava tubes within lava flows no. 1–2, which fed breakouts that resurfaced N19 km2 of the flow field. The primary lava morphology from this phase was spiny pāhoehoe, which superimposed on the ‘a’ā lava flows no. 1–3 and extended the entire length of the flow field (i.e. 17 km). Thismade the 2014–2015 Holuhraun a paired flow field,where both lava morphologies had similar length. We suggest that the similar length is a consequence of the pāhoehoe is fed from the tube systemutilizing the existing ‘a’ā lava channels, and thereby are controlled by the initial length of the ‘a’ā flows.The work was financed with crisis response funding from the Icelandic Government along with European Community's Seventh Framework Programme Grant No. 308377 (Project FUTUREVOLC) and along with the Icelandic Research fund, Rannis, Grant of Excellence No. 152266-052 (Project EMMIRS). Furthermore, Vinur Vatnajökuls are thanked for support.Peer Reviewe

Predicting Missing Links via Local Information

Missing link prediction of networks is of both theoretical interest and practical significance in modern science. In this paper, we empirically investigate a simple framework of link prediction on the basis of node similarity. We compare nine well-known local similarity measures on six real networks. The results indicate that the simplest measure, namely common neighbors, has the best overall performance, and the Adamic-Adar index performs the second best. A new similarity measure, motivated by the resource allocation process taking place on networks, is proposed and shown to have higher prediction accuracy than common neighbors. It is found that many links are assigned same scores if only the information of the nearest neighbors is used. We therefore design another new measure exploited information of the next nearest neighbors, which can remarkably enhance the prediction accuracy.Comment: For International Workshop: "The Physics Approach To Risk: Agent-Based Models and Networks", http://intern.sg.ethz.ch/cost-p10

Holocene Cyclic Records of Ice-Rafted Debris and Sea Ice Variations on the East Greenland and Northwest Iceland Margins

The dynamics of the Greenland Ice Sheet and drift of sea ice from the Arctic Ocean reaching Denmark Strait are poorly constrained. We present data on the provenance of Fe oxide detrital grains from two cores in the Denmark Strait area and compare the Fe grain source data with other environmental proxies in order to document the variations and potential periodicities in ice-rafted debris delivery during the Holocene. Based on their Fe grain geochemistry, the sediments can be traced to East Greenland sources and to more distal sites around the Arctic Basin. On the Holocene time scales of the two cores, sea ice biomarker (IP25) data, and quartz weight percent reveal positive associations with T°C and inverse associations with biogenic carbonate wt%. Trends in the data were obtained from Singular Spectrum Analysis (SSA), and residuals were tested for cyclicity. Trends on the environmental proxies explained between 15 and 90% of the variance. At both sites the primary Fe grain sources were from Greenland, but significant contributions were also noted from Banks Island and Svalbard. There is a prominent cyclicity of 800 yrs as well as other less prominent cycles for both Greenland and arctic sources. The Fe grain sources from Greenland and the circum-Arctic Ocean are in synchronization, suggesting that the forcings for these cycles are regional and not local ice sheet instabilities