Integral equation mei applied to three-dimensional arbitrary surfaces

The authors present a new formulation of the integral equation of the measured equation of invariance (MEI) as a confined field integral equation discretised by the method of moments, in which the use of numerically derived testing functions results in an approximately sparse linear system with storage memory requirements and a CPU time for computing the matrix coefficients proportional to the number of unknowns.Peer ReviewedPostprint (published version

Analysis of microstrip antennas by multilevel matrix decomposition algorithm

Integral equation methods (IE) are widely used in conjunction with Method of Moments (MoM) discretization for the numerical analysis of microstrip antennas. However, their application to large antenna arrays is difficult due to the fact that the computational requirements increase rapidly with the number of unknowns N. Several techniques have been proposed to reduce the computational cost of IE-MoM. The Multilevel Matrix Decomposition Algorithm (MLMDA) has been implemented in 3D for arbitrary perfectly conducting surfaces discretized in Rao, Wilton and Glisson linear triangle basis functions . This algorithm requires an operation count that is proportional to N·log2N. The performance of the algorithm is much better for planar or piece-wise planar objects than for general 3D problems, which makes the algorithm particularly well-suited for the analysis of microstrip antennas. The memory requirements are proportional to N·logN and very low. The main advantage of the MLMDA compared with other efficient techniques to solve integral equations is that it does not rely on specific mathematical properties of the Green's functions being used. Thus, we can apply the method to interesting configurations governed by special Green's functions like multilayered media. In fact, the MDA-MLMDA method can be used at the top of any existing MoM code. In this paper we present the application to the analysis of large printed antenna arrays.Peer ReviewedPostprint (published version

Spatial and temporal stability of weed patches in cereal fields under direct drilling and harrow tillage

The adoption of conservation agriculture (CA) techniques by farmers is changing the dynamics of weed communities in cereal fields and so potentially their spatial distribution. These changes can challenge the use of site-specific weed control, which is based on the accurate location of weed patches for spraying. We studied the effect of two types of CA (direct drilling and harrow-tilled to 20 cm) on weed patches in a three-year survey in four direct-drilled and three harrow-tilled commercial fields in Catalonia (North-eastern Spain). The area of the ground covered by weeds (hereafter called “weed cover”) was estimated at 96 to 122 points measured in each year in each field, in 50 cm × 50 cm quadrats placed in a 10 m × 10 m grid in spring. Bromus diandrus, Lolium rigidum, and Papaver rhoeas were the main weed species. The weed cover and degree of aggregation for all species varied both between and within fields, regardless of the kind of tillage. Under both forms of soil management all three were aggregated in elongated patterns in the direction of traffic. Bromus was generally more aggregated than Lolium, and both were more aggregated than Papaver. Patches were stable over time for only two harrow-tilled fields with Lolium and one direct-drilled field with Bromus, but not in the other fields. Spatial stability of the weeds was more pronounced in the direction of traffic. Herbicide applications, crop rotation, and traffic seem to affect weed populations strongly within fields, regardless of the soil management. We conclude that site-specific herbicides can be applied to control these species because they are aggregated, although the patches would have to be identified afresh in each season.This research was funded by the Spanish National Program (project: AGL2010-22084-C02-0). A.E.M. was funded by the Institute Strategic Programme (ISP) grants, “Soils to Nutrition” (S2N) grant number BBS/E/C/000I0330, and the joint Natural Environment Research Council (NERC) and Biotechnology and Biological Sciences Research Council (BBSRC) ISP grant “Achieving Sustainable Agricultural Systems” (ASSIST) grant number BBS/E/C/000I0100, using facilities funded by the BBSRC

Matroids and Quantum Secret Sharing Schemes

A secret sharing scheme is a cryptographic protocol to distribute a secret state in an encoded form among a group of players such that only authorized subsets of the players can reconstruct the secret. Classically, efficient secret sharing schemes have been shown to be induced by matroids. Furthermore, access structures of such schemes can be characterized by an excluded minor relation. No such relations are known for quantum secret sharing schemes. In this paper we take the first steps toward a matroidal characterization of quantum secret sharing schemes. In addition to providing a new perspective on quantum secret sharing schemes, this characterization has important benefits. While previous work has shown how to construct quantum secret sharing schemes for general access structures, these schemes are not claimed to be efficient. In this context the present results prove to be useful; they enable us to construct efficient quantum secret sharing schemes for many general access structures. More precisely, we show that an identically self-dual matroid that is representable over a finite field induces a pure state quantum secret sharing scheme with information rate one

Microplate tectonics and environmental factors as distribution drivers in Western Mediterranean freshwater planarians

AIM: Species biogeography mainly focuses on palaeogeographical events, while environmental factors are generally overlooked despite their importance in species diversification. Here, we use an integrative approach to understand how palaeogeographical and environmental processes shape species distribution and focus on freshwater planarians as the model system. LOCATION: Western Mediterranean. TAXON: Dugesia METHODS: We inferred the phylogenetic relationships of most known Dugesia species in the area using six molecular markers. We then estimated their divergence times and reconstructed their ancestral distribution ranges. We also performed environmental niche modelling analyses using Dugesia subtentaculata as a model to evaluate the effects of several hydro-environmental variables and the likely existence of interspecific competition on Dugesia distributions. RESULTS: Our results provide a new phylogenetic scheme for Dugesia from the Western Mediterranean and show that the time splits between the lineages and their putative ancestral distribution ranges are correlated with microplate tectonic dynamics within the region during the Oligocene–Miocene period. Our environmental niche modelling analyses indicate that the type of land cover and the slope of the terrain are the most important abiotic factors driving the distribution of Dugesia from this region. Finally, we found a partial niche overlap between D. subtentaculata and two other common planarian species from the Iberian Peninsula. MAIN CONCLUSIONS: The microplate tectonic dynamics of the Western Mediterranean during the Oligocene–Miocene period, together with the position of the mountain ranges and posterior climate changes, may have played crucial roles in driving the biogeographical history of Dugesia in this region. Moreover, both interspecific competition and changes in fluvial characteristics driven by human activities may affect the current diversity and distribution of Dugesia in the Western Mediterranean. This study highlights the importance of integrating different types of information to study the biogeographical history of a species. <br

Children's biobehavioral reactivity to challenge predicts DNA methylation in adolescence and emerging adulthood.

A growing body of research has documented associations between adverse childhood environments and DNA methylation, highlighting epigenetic processes as potential mechanisms through which early external contexts influence health across the life course. The present study tested a complementary hypothesis: indicators of children's early internal, biological, and behavioral responses to stressful challenges may also be linked to stable patterns of DNA methylation later in life. Children's autonomic nervous system reactivity, temperament, and mental health symptoms were prospectively assessed from infancy through early childhood, and principal components analysis (PCA) was applied to derive composites of biological and behavioral reactivity. Buccal epithelial cells were collected from participants at 15 and 18 years of age. Findings revealed an association between early life biobehavioral inhibition/disinhibition and DNA methylation across many genes. Notably, reactive, inhibited children were found to have decreased DNA methylation of the DLX5 and IGF2 genes at both time points, as compared to non-reactive, disinhibited children. Results of the present study are provisional but suggest that the gene's profile of DNA methylation may constitute a biomarker of normative or potentially pathological differences in reactivity. Overall, findings provide a foundation for future research to explore relations among epigenetic processes and differences in both individual-level biobehavioral risk and qualities of the early, external childhood environment