497 research outputs found

    Modeling Aerial Gamma-Ray Backgrounds using Non-negative Matrix Factorization

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    Airborne gamma-ray surveys are useful for many applications, ranging from geology and mining to public health and nuclear security. In all these contexts, the ability to decompose a measured spectrum into a linear combination of background source terms can provide useful insights into the data and lead to improvements over techniques that use spectral energy windows. Multiple methods for the linear decomposition of spectra exist but are subject to various drawbacks, such as allowing negative photon fluxes or requiring detailed Monte Carlo modeling. We propose using Non-negative Matrix Factorization (NMF) as a data-driven approach to spectral decomposition. Using aerial surveys that include flights over water, we demonstrate that the mathematical approach of NMF finds physically relevant structure in aerial gamma-ray background, namely that measured spectra can be expressed as the sum of nearby terrestrial emission, distant terrestrial emission, and radon and cosmic emission. These NMF background components are compared to the background components obtained using Noise-Adjusted Singular Value Decomposition (NASVD), which contain negative photon fluxes and thus do not represent emission spectra in as straightforward a way. Finally, we comment on potential areas of research that are enabled by NMF decompositions, such as new approaches to spectral anomaly detection and data fusion.Comment: 14 pages, 12 figures, accepted for publication in IEEE Transactions on Nuclear Scienc

    Decoding Anotylus (Thomson 1859) Beetle Diversity: DNA and External Morphology Match in Área de Conservacion Guanacaste, Costa Rica

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    Taxonomy underpins biological research because names are needed for comparative analysis, conservation status, and public communication. Despite this, many species remain undescribed and are therefore vulnerable and unprotected, particularly in the tropics. Neotropical Staphylinidae beetles (Coleoptera) are among the insect groups most likely to contain significant unknown and/or cryptic diversity. Here we used an integrative taxonomic framework to conduct a preliminary review of one particularly diverse genus of Staphylinidae (Anotylus) in Área de Conservaciόn Guanacaste, northwestern Costa Rica. We began by DNA barcoding novel collections and using Barcode Index Numbers (BINs) as an estimate of taxonomic diversity; we found 18 provisional new species. We augmented this genetic analysis with a morphometric analysis of adult morphological characters and found that we could differentiate most provisional species by external morphology as well as by elevation of collection. All the most abundant species could be differentiated from each other by differences in body size. One BIN included slight (~1%) genetic variation that corresponded with some morphological differentiation suggesting the existence of two species within a DNA BIN. Our results support the efficacy of DNA barcoding collections of tropical insects as an effective biodiversity estimator, one that can be used as a primer for integrative taxonomic studies using BINs as species hypotheses

    Evaluating Functional Diversity as Potential Early-Warning Indicator of Rangeland Degradation

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    Droughts and overgrazing play a crucial role in the degradation of semi-arid rangelands. This is evident in the loss of palatable long-lived grass species and bush encroachment. Early warning indicators are needed to mitigate long-term degradation and decline in essential forage provision. Functional diversity provides valuable information on ecosystem health. However, functional diversity indices have not yet been tested regarding their applicability as early warning indicators, revealing non-linear threshold behaviour. We therefore examined the following questions: (1) How do functional diversity indices respond to grazing pressure? (2) Does land tenure affect the relationship between functional diversity and grazing pressure? (3) Are functional diversity indices suitable early-warning indicators? To answer these questions, we conducted a space-for-time substitution of land use intensity of semi-arid rangelands in Namibia. Some 16 grazing gradients were selected, each starting at a cattle watering point where grazing pressure was highest. Gradients were located in four communal and four freehold farms. Communal farms were characterised by continuous grazing, while freehold farms by rotational grazing. In each transect we recorded plant species composition of the grass layer in 9 plots of 10 × 10 m each (N = 162 plots). Within each transect, these plots were logarithmically distributed. Various plant functional traits—all relating to plant life history or resource acquisition strategy—were measured for 142 dominant species, accounting for more than 80 % of the biomass, and indices of functional diversity were calculated. We found potential threshold behaviour in functional richness on freehold farms. Certain functional diversity indices revealed non-linear patterns in rangelands but are currently not a user-friendly early-warning indicator. To harness functional diversity, we need a more standardized method of calculation, and more functional trait databases for sub-Saharan species

    Seeking structural repetitivity in systems with interaction interference: crystal engineering in the gem-alkynol family

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    Synthon repetitivity has been demonstrated in a pair of gem-alkynols, despite the high degree of interaction interference typical of this family of compounds

    When is a polymorph not a polymorph? Helical trimeric O-H···O synthons in trans-1,4-diethynylcyclohexane-1,4-diol

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    Two polymorphs (A and B) of trans-1,4-diethynylcyclohexane-1,4-diol represent a unique example of the simultaneous occurrence of both conformational polymorphism and conformational isomorphism, while a pseudopolymorphic monohydrate is closely related

    The distribution of pond snail communities across a landscape: separating out the influence of spatial position from local habitat quality for ponds in south-east Northumberland, UK

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    Ponds support a rich biodiversity because the heterogeneity of individual ponds creates, at the landscape scale, a diversity of habitats for wildlife. The distribution of pond animals and plants will be influenced by both the local conditions within a pond and the spatial distribution of ponds across the landscape. Separating out the local from the spatial is difficult because the two are often linked. Pond snails are likely to be affected by both local conditions, e.g. water hardness, and spatial patterns, e.g. distance between ponds, but studies of snail communities struggle distinguishing between the two. In this study, communities of snails were recorded from 52 ponds in a biogeographically coherent landscape in north-east England. The distribution of snail communities was compared to local environments characterised by the macrophyte communities within each pond and to the spatial pattern of ponds throughout the landscape. Mantel tests were used to partial out the local versus the landscape respective influences. Snail communities became more similar in ponds that were closer together and in ponds with similar macrophyte communities as both the local and the landscape scale were important for this group of animals. Data were collected from several types of ponds, including those created on nature reserves specifically for wildlife, old field ponds (at least 150 years old) primarily created for watering livestock and subsidence ponds outside protected areas or amongst coastal dunes. No one pond type supported all the species. Larger, deeper ponds on nature reserves had the highest numbers of species within individual ponds but shallow, temporary sites on farm land supported a distinct temporary water fauna. The conservation of pond snails in this region requires a diversity of pond types rather than one idealised type and ponds scattered throughout the area at a variety of sites, not just concentrated on nature reserves
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