39 research outputs found
Mismatches in scale between highly mobile marine megafauna and marine protected areas
Marine protected areas (MPAs), particularly large MPAs, are increasing in number and size around the globe in part to facilitate the conservation of marine megafauna under the assumption that large-scale MPAs better align with vagile life histories; however, this alignment is not well established. Using a global tracking dataset from 36 species across five taxa, chosen to reflect the span of home range size in highly mobile marine megafauna, we show most MPAs are too small to encompass complete home ranges of most species. Based on size alone, 40% of existing MPAs could encompass the home ranges of the smallest ranged species, while only \u3c 1% of existing MPAs could encompass those of the largest ranged species. Further, where home ranges and MPAs overlapped in real geographic space, MPAs encompassed \u3c 5% of core areas used by all species. Despite most home ranges of mobile marine megafauna being much larger than existing MPAs, we demonstrate how benefits from MPAs are still likely to accrue by targeting seasonal aggregations and critical life history stages and through other management techniques
The redmapper galaxy cluster catalog from DES Science Verification data
We describe updates to the redMaPPer algorithm, a photometric red-sequence cluster finder specifically designed for large photometric surveys. The updated algorithm is applied to 150 {{deg}}2 of Science Verification (SV) data from the Dark Energy Survey (DES), and to the Sloan Digital Sky Survey (SDSS) DR8 photometric data set. The DES SV catalog is locally volume limited and contains 786 clusters with richness lambda \gt 20 (roughly equivalent to {M}{{500c}}≳ {10}14 {h}70-1 {M}o ) and 0.2\lt z\lt 0.9. The DR8 catalog consists of 26,311 clusters with 0.08\lt z\lt 0.6, with a sharply increasing richness threshold as a function of redshift for z≳ 0.35. The photometric redshift performance of both catalogs is shown to be excellent, with photometric redshift uncertainties controlled at the {sigma }z/(1+z)~ 0.01 level for z≲ 0.7, rising to ~0.02 at z~ 0.9 in DES SV. We make use of Chandra and XMM X-ray and South Pole Telescope Sunyaev--Zeldovich data to show that the centering performance and mass--richness scatter are consistent with expectations based on prior runs of redMaPPer on SDSS data. We also show how the redMaPPer photo-z and richness estimates are relatively insensitive to imperfect star/galaxy separation and small-scale star masks
Erratum to: 36th International Symposium on Intensive Care and Emergency Medicine
[This corrects the article DOI: 10.1186/s13054-016-1208-6.]
Generalization of non-iterative numerical methods for damage-plastic behaviour modeling
Modelling fracture in concrete or masonry is known to be problematic regarding the robustness of iterative solution procedures and, the use of non-iterative methods (or that minimize the use of iterations) in quasi-brittle materials is now under strong development, due to the necessity to obtain effective results in finite element analysis [1, 2] where strong non-linearities emerge that are otherwise unwieldy to model. In the proposed lecture, two new methods designated as Non-Iterative Energy based Method (NIEM) and Automatic presented in [1, 3] are applied with extension to modelling damage-plastic behaviour. The new methods combine an incremental-total procedure with the preferential use of incremental steps, switching to the total approach only at critical bifurcation points. The development of the load-unloading abilities is allowed by these incremental/total methods, which take advantage of keeping the material’s stress/strain memory due to the preferential use of an incremental procedure. A new approach to the unload-load cycles is used in the scope of a noniterative procedure, which will mitigate the numerical difficulties inherent to cyclic loading. The formulation for both methods for structures with both softening and hardening behaviour is presented and a structural example where the numerical results are compared with experimental results.Structural EngineeringCivil Engineering and Geoscience
A generalized discrete strong discontinuity approach
Several local embedded discontinuity formulations have already been developed, in which constant strain triangles and constant jumps are adopted. However, these formulations lead to jump and traction discontinuity across element boundaries and stress locking effects. Herein, a new contribution to embedded strong discontinuities is given. A generalized discrete strong discontinuity approach (GSDA) is presented, in which non-homogeneous jumps can be embedded in any type of parent finite elements. A comparison to the generalized finite element method (GFEM) is also established. With this new formulation the additional degrees of freedom are global and continuous jumps and tractions across the element boundaries are always obtained. The kinematics of the GSDA accurately reproduces both rigid-body motion and stretching induced by the opening of a discontinuity. Some simple examples are presented to illustrate the ability of this formulation in reproducing different opening modes. Structural examples, involving both mode-I and mixed-mode fracture, are also simulated and compared to experimental results.Structural EngineeringCivil Engineering and Geoscience
Numerical modelling of the shear strength between concrete layers
Some of the most used strengthening techniques for reinforced concrete structures include the increase of existing cross-sections. The monolithic behaviour of the strengthened elements depends basically on the interface between the substrate and the new concrete layer. A complete numerical model capable of dealing with the composite response of these RC elements is still missing. Such a model mainly depends on the interface behaviour, namely shear friction and dowel action. A numerical model is calibrated using experimental data carried out to assess the longitudinal shear strength between two concrete layers with different values of added rein- forcement. A parametric study is developed to identify the influence of the following parameters on the interface behaviour: elastic stiffness; cohesion; internal friction angle; fracture energy; dilatancy; steel constitutive law and the bond-slip relation between connectors and concrete. The role of each parameter is clarified and the most relevant conclusions are presented.Structural EngineeringCivil Engineering and Geoscience
State space modeling of fluid flow for thrust control in mems-based micropropulsion
This paper presents a dynamic system approach for the modeling of fluid flow in microchannels to be used in thrust control applications. A micro-resistojet fabricated using MEMS (Microelectromechanical Systems) technology has been selected for the analysis. The device operates by vaporizing a liquid propellant, in this case water, and expelling it as gas that is accelerated by a micro-nozzle. The pressure variation due to boiling in the chamber might lead to unwanted behavior of the feed system and the frequency analysis in this case can indicate whether or not instabilities will be present. To handle this complex problem, the incompressible Navier-Stokes equations are linearized in the steady-state flow regime and then formulated in state space form to provide the necessary means for control analysis. Controllability and observability of the system are investigated considering low values of Reynolds numbers present in micro fluidics applications. Results from the analytical treatment are compared with CFD (Computational Fluid Dynamics) simulations of the microchannel to demonstrate the validity of the approach investigatedSpace Systems Egineerin
Conforming finite elements with embedded strong discontinuities
The possibility of embedding strong discontinuities into finite elements allowed the simulation of different problems, namely, brickwork masonry fracture, dynamic fracture, failure in finite strain problems and simulation of reinforcement concrete members. However, despite the significant contributions to this field, a general embedded formulation capable of dealing with strong discontinuities using conforming finite elements is still missing. Therefore a new conforming embedded formulation is herein proposed and compared with other relevant formulations, namely the Generalised Strong Discontinuity Approach (GSDA) [1] and the Generalised/Extended Finite Element Method (GFEM/XFEM) [2-5]. Academic and structural examples are given in order to illustrate the capabilities of the proposed approach in comparison with GSDA and GFEM/XFEM. In summary, the proposed formulation has the following properties: i) variational consistency; ii) no limitations on the choice of the parent finite element; iii) comprehensive kinematics of the discontinuity, including both rigid body motion and stretching; iv) fully compatible enhanced kinematic field; v) additional degrees of freedom located at the discontinuity; vi) continuity of both jumps and tractions across element boundaries; and vii) stress locking free.Structural EngineeringCivil Engineering and Geoscience