A locking-free face-centred finite volume (FCFV) method for linear elastostatics

A face-centred finite volume (FCFV) method is proposed for linear elastostatic problems. The FCFV is a mixed hybrid formulation, featuring a system of first-order equations, that defines the unknowns on the faces (edges in two dimensions) of the mesh cells. The symmetry of the stress tensor is strongly enforced using the well-known Voigt notation and the displacement and stress fields inside each cell are obtained by means of explicit formulas. The resulting FCFV method is robust and locking-free in the nearly incompressible limit. Numerical experiments in two and three dimensions show optimal convergence of the displacement and the stress fields without any reconstruction. Moreover, the accuracy of the FCFV method is not sensitive to mesh distortion and stretching. Classical benchmark tests including Kirch’s plate and Cook’s membrane problems in two dimensions as well as three dimensional problems involving shear phenomenons, pressurised thin shells and complex geometries are presented to show the capability and potential of the proposed methodology

Multi-dimensional modeling and simulation of semiconductor nanophotonic devices

Self-consistent modeling and multi-dimensional simulation of semiconductor nanophotonic devices is an important tool in the development of future integrated light sources and quantum devices. Simulations can guide important technological decisions by revealing performance bottlenecks in new device concepts, contribute to their understanding and help to theoretically explore their optimization potential. The efficient implementation of multi-dimensional numerical simulations for computer-aided design tasks requires sophisticated numerical methods and modeling techniques. We review recent advances in device-scale modeling of quantum dot based single-photon sources and laser diodes by self-consistently coupling the optical Maxwell equations with semiclassical carrier transport models using semi-classical and fully quantum mechanical descriptions of the optically active region, respectively. For the simulation of realistic devices with complex, multi-dimensional geometries, we have developed a novel hp-adaptive finite element approach for the optical Maxwell equations, using mixed meshes adapted to the multi-scale properties of the photonic structures. For electrically driven devices, we introduced novel discretization and parameter-embedding techniques to solve the drift-diffusion system for strongly degenerate semiconductors at cryogenic temperature. Our methodical advances are demonstrated on various applications, including vertical-cavity surface-emitting lasers, grating couplers and single-photon sources

Tree diversity increases levels of herbivore damage in a subtropical forest canopy: evidence for dietary mixing by arthropods?

Aims Plant diversity has been linked to both increasing and decreasing levels of arthropod herbivore damage in different plant communities. So far, these links have mainly been studied in grasslands or in artificial tree plantations with low species richness. Furthermore, most studies provide results from newly established experimental plant communities where trophic links are not fully established or from stands of tree saplings that have not yet developed a canopy. Here, we test how tree diversity in a species-rich subtropical forest in China with fully developed tree canopy affects levels of herbivore damage caused by different arthropod feeding guilds. Methods We established 27 plots of 30×30 m area. The plots were selected randomly but with the constraint that they had to span a large range of tree diversity as required for comparative studies in contrast to sample surveys. We recorded herbivore damage caused by arthropod feeding guilds (leaf chewers, leaf skeletonizers and sap feeders) on canopy leaves of all major tree species. Important Findings Levels of herbivore damage increased with tree species richness and tree phylogenetic diversity. These effects were most pronounced for damage caused by leaf chewers. Although the two diversity measures were highly correlated, we additionally found a significant interaction between them, whereby species richness increased herbivory mostly at low levels of phylogenetic diversity. Tree species with the lowest proportion of canopy leaf biomass in a plot tended to suffer the highest levels of herbivore damage, which is in contrast to expectations based on the resource concentration hypothesis. Our results are in agreement with expectations of the dietary mixing hypothesis where generalist herbivores with a broad spectrum of food plants benefit from increased resource diversity in tree species-rich forest patches

Optimal convergence of a discontinuous-Galerkin-based immersed boundary method

We prove the optimal convergence of a discontinuous-Galerkin-based immersed boundary method introduced earlier [Lew and Buscaglia, Int. J. Numer. Methods Eng. 76 (2008) 427–454]. By switching to a discontinuous Galerkin discretization near the boundary, this method overcomes the suboptimal convergence rate that may arise in immersed boundary methods when strongly imposing essential boundary conditions. We consider a model Poisson's problem with homogeneous boundary conditions over two-dimensional C2-domains. For solution in Hq for q > 2, we prove that the method constructed with polynomials of degree one on each element approximates the function and its gradient with optimal orders h2 and h, respectively. When q = 2, we have h2-ε and h1-ε for any ϵ > 0 instead. To this end, we construct a new interpolant that takes advantage of the discontinuities in the space, since standard interpolation estimates lead here to suboptimal approximation rates. The interpolation error estimate is based on proving an analog to Deny-Lions' lemma for discontinuous interpolants on a patch formed by the reference elements of any element and its three face-sharing neighbors. Consistency errors arising due to differences between the exact and the approximate domains are treated using Hardy's inequality together with more standard results on Sobolev functions

Tree diversity drives diversity of arthropod herbivores, but successional stage mediates detritivores

The high tree diversity of subtropical forests is linked to the biodiversity of other trophic levels. Disentangling the effects of tree species richness and composition, forest age, and stand structure on higher trophic levels in a forest landscape is important for understanding the factors that promote biodiversity and ecosystem functioning. Using a plot network spanning gradients of tree diversity and secondary succession in subtropical forest, we tested the effects of tree community characteristics (species richness and composition) and forest succession (stand age) on arthropod community characteristics (morphotype diversity, abundance and composition) of four arthropod functional groups. We posit that these gradients differentially affect the arthropod functional groups, which mediates the diversity, composition, and abundance of arthropods in subtropical forests. We found that herbivore richness was positively related to tree species richness. Furthermore, the composition of herbivore communities was associated with tree species composition. In contrast, detritivore richness and composition was associated with stand age instead of tree diversity. Predator and pollinator richness and abundance were not strongly related to either gradient, although positive trends with tree species richness were found for predators. The weaker effect of tree diversity on predators suggests a cascading diversity effect from trees to herbivores to predators. Our results suggest that arthropod diversity in a subtropical forest reflects the net outcome of complex interactions among variables associated with tree diversity and stand age. Despite this complexity, there are clear linkages between the overall richness and composition of tree and arthropod communities, in particular herbivores, demonstrating that these trophic levels directly impact each other

The Gavon basin: a model of post-glacial debris-flow

The Gavon basin hosts one of the major landslide deposits of the Eastern Italian Dolomites (Falcade, Belluno). This deposit is due to different phases of erosion carried out by the Gavon, which is a sinistral tributary of the Cordevole River, and it consists of a thick erodible sequence of Upper Permian Bellerophon Formation and Lower Triassic Werfen Formation (divided into Tesero, Mazzin, Andraz, Siusi, Gastropod Oolite, Campil, Val Badia, Cencenighe, San Lucano Members) that have been tectonically duplicated by thrust activity and uplifted by two superposed folding and diapiric deformations, rising the sequence to an elevation of 2499 meters a.s.l. at the Forca Rossa pass. The Gavon basin is 5.98 km long and is characterized by a mean slope greater than 18%. The Lower Triassic sequence was eroded producing a 7.86 km2 basin in pre-glacial time. The basin was filled up by early landslide deposits before the last glaciation, which onset date back to about 30 thousand years before present, and during historic time. The catchment is now subjected to high erosion due to the frequent rainfall/snowfall events. The solid transport has always been high (up to 34400 m3/y) and, for this reason, some dams were built 80 years ago. Three more check dams were built in 2005 to further decrease the erosion. A reconstruction of the events in the postglacial time is carried out based on (a) the volume of the deposits and (b) the missing volume in the detachment area. A volume of 173 to 216 million cubic meters has been eroded by a series of events (or a unique large event) that ended approximately 4000 years ago (Fenti, 2018). To complete this analysis, we numerically modelled the detachment and runout of a block of rock located in the top portion of the basin, where some tension cracks are now evident, and assuming that an intense rain event could mobilize it. The analysis has been processed using LiDAR data with QGis software, while the simulations are performed with GeoFlow-SPH

Martin, Emma. Interview about the early days of Port Union.

Transcript and digitized audio recording from a collection belonging to the Sir William F. Coaker Heritage Foundation. Martin discusses her upbringing in Port Union, including specific memories about the buildings and operations of the FPU