8,034 research outputs found
The second Feng-Rao number for codes coming from telescopic semigroups
In this manuscript we show that the second Feng-Rao number of any telescopic
numerical semigroup agrees with the multiplicity of the semigroup. To achieve
this result we first study the behavior of Ap\'ery sets under gluings of
numerical semigroups. These results provide a bound for the second Hamming
weight of one-point Algebraic Geometry codes, which improves upon other
estimates such as the Griesmer Order Bound
Low molecular weight ϵ-caprolactone-pcoumaric acid copolymers as potential biomaterials for skin regeneration applications
ϵ-caprolactone-p-coumaric acid copolymers at different mole ratios (ϵ-caprolactone:p-coumaric acid 1:0, 10:1, 8:1, 6:1, 4:1, and 2:1) were synthesized by melt-polycondensation and using 4-dodecylbenzene sulfonic acid as catalyst. Chemical analysis by NMR and GPC showed that copolyesters were formed with decreasing molecular weight as p-coumaric acid content was increased. Physical characteristics, such as thermal and mechanical properties, as well as water uptake and water permeability, depended on the mole fraction of pcoumaric acid. The p-coumarate repetitive units increased the antioxidant capacity of the copolymers, showing antibacterial activity against the common pathogen Escherichia coli. In addition, all the synthesized copolyesters, except the one with the highest concentration of the phenolic acid, were cytocompatible and hemocompatible, thus becoming potentially useful for skin regeneration applications
Upscaling of bottom-generated turbulence in large-scale 3D models for sediment transport in estuaries and coastal zones
Currently used 3D numerical sediment transport models still fail to make good quantitative predictions. To a great extent, this can be attributed to the inadequate description of physical processes which occur at the subgrid scale level. From flume experiments it is known that particle-turbulence interactions near the bed significantly change the effective roughness experienced by the overlying water column. This results in different transport rates if not accounted for.From a theoretical perspective, bed load transport, sheet flow and fluid mud flow are all occurrences of supersaturated suspension flow in the inner near-bed layer comprising the viscous sublayer and the transient layer. Its thickness increases with sediment load, since particle-particle interactions (four-way coupling effects) consume considerable amounts of the available stream power. In order to know how much energy is left over to compute the transport capacity of the outer, fully-developed layer, it is necessary to quantify the energy budget in the inner layer.This is a difficult task. Every modelling approach has its draw-backs and limitations. Lagrangean particle tracking is hopeless, since the required number of particles to approach field conditions is much too high, and the volumes occupied by the particles cannot be neglected. Grain sizes are non-uniform in nature and concentrations near the bed very high, making it very difficult to give an accurate description of the momentum exchange between fluid and solid phase, which accounts for particle collisions. Therefore, in view of large-scale applications, a one-fluid approach is adopted. This implies that the momentum equation is solved for the suspension, together with a turbulence closure model and the sediment mass balance.Since the thickness of the supersaturated inner layer mostly is very small relative to the water depth and the vertical discretization in large scale applications, it is not possible to resolve this layer with a traditional low-Reynolds model approach, which requires a very fine grid. A new approach is proposed, where a modified Prandtl-mixing length (PML) model is used for the bed layer, and a new low-Reynolds model is applied in the outer layers. In this way it is possible to obtain a correct behaviour for tidal oscillating flow in estuaries, where low-Re effects enter high in the water column during slack water.The correction factor for the PML eddy viscosity and the damping functions for the low-Re k-epsilon turbulence model are constructed based on theoretical constraints, DNS and LES generated data, as well as experimental flume data. In parallel, LES and improved two-layer low-Re models are developed to simulate flow over rough bottoms without and with sediment, in order to generate data very close to the bed surface, where no measurements can be made. These additional data are used to help interpret experimental flume data, which always show relatively high experimental errors, and to extend the new damping functions for the cases with bottom roughness and suspended sediment.Preliminary results of the new coarse grid RANS model for open-channel flow with various roughness conditions without and with suspended sediment will be shown, compared to LES results for flow over a wavy bottom, low-Reynolds RANS results over rough bottom and experimental flume data
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Crops gone wild: evolution of weeds and invasives from domesticated ancestors.
The evolution of problematic plants, both weeds and invasives, is a topic of increasing interest. Plants that have evolved from domesticated ancestors have certain advantages for study. Because of their economic importance, domesticated plants are generally well-characterized and readily available for ecogenetic comparison with their wild descendants. Thus, the evolutionary history of crop descendants has the potential to be reconstructed in some detail. Furthermore, growing crop progenitors with their problematic descendants in a common environment allows for the identification of significant evolutionary differences that correlate with weediness or invasiveness. We sought well-established examples of invasives and weeds for which genetic and/or ethnobotanical evidence has confirmed their evolution from domesticates. We found surprisingly few cases, only 13. We examine our list for generalizations and then some selected cases to reveal how plant pests have evolved from domesticates. Despite their potential utility, crop descendants remain underexploited for evolutionary study. Promising evolutionary research opportunities for these systems are abundant and worthy of pursuit
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