168 research outputs found
History and geography of neotropical tree diversity
This is the author accepted manuscript. The final version is available from Annual Reviews via the DOI in this record Early botanical explorers invoked biogeographic history to explain the remarkable tree diversity of Neotropical forests. In this context, we review the history of Neotropical tree diversity over the past 100 million years, focusing on biomes with significant tree diversity. We evaluate hypotheses for rain forest origins, intercontinental disjunctions, and models of Neotropical tree diversification. To assess the impact of biotic interchange on the Amazon tree flora, we examined biogeographic histories of trees in Ecuador's Yasuní Forest, which suggest that nearly 50% of its species descend from immigrant lineages that colonized South America during the Cenozoic. Long-distance and intercontinental dispersal, combined with trait filtering and niche evolution, are important factors in the community assembly of Neotropical forests. We evaluate the role of pre-Columbian people on Neotropical tree diversity and discuss the future of Neotropical forests in the Anthropocene.NASANSFNatural Environment Research CouncilNERC NewtonFAPESPOrganization for Tropical StudiesNEscen
Long-term TNT and DNT contamination: 1-D modeling of natural attenuation in the vadose zone: case study, Portugal
The vadose zone of a trinitrotoluene (TNT) and dinitrotoluene (DNT) contaminated site was investigated to assess the mobility of those explosives under natural conditions. Located in the left margin of the River Tejo Basin, Portugal, the site is located on unconsolidated sediments. Wastewaters associated with the 50-year explosives production were disposed in excavated ponds, from where water would infiltrate and pollute the unsaturated and saturated parts of the local aquifers. Two boreholes were drilled to 9 m depth in such a former waste pond to investigate the contaminant's fate in the vadose zone. Sediment samples were taken every 1-2 m for analysis of the polynitroaromatics (p-NACs) and organic volatile compounds, pH, organic carbon content, cation exchange capacity and grain size analysis. The main contaminant was TNT representing >70 % of the total p-NACs concentration that peaked approximately 7 mg/kg in one borehole, even if the median in both boreholes was of similar to 1 mg/kg. DNT was 4-30 % of the total p-NACs and nitrotoluene (NT), up to 5 %. No other (volatile) organic compound was detected. The predominance of TNT as the main contaminant implies that any natural mass reduction has been inefficient to clean the site. Several 1-D model simulations of p-NACs cleaning of the vadose zone under natural conditions indicated that the most probable scenario of combined advection and partitioning will only remove TNT after 10's of years, whereas DNT and NT will hardly be removed. Such low concentrations and long times for the p-NACs removal, suggest that by now those compounds have been washed-out to a level below standard limits
Single-valued harmonic polylogarithms and the multi-Regge limit
We argue that the natural functions for describing the multi-Regge limit of
six-gluon scattering in planar N=4 super Yang-Mills theory are the
single-valued harmonic polylogarithmic functions introduced by Brown. These
functions depend on a single complex variable and its conjugate, (w,w*). Using
these functions, and formulas due to Fadin, Lipatov and Prygarin, we determine
the six-gluon MHV remainder function in the leading-logarithmic approximation
(LLA) in this limit through ten loops, and the next-to-LLA (NLLA) terms through
nine loops. In separate work, we have determined the symbol of the four-loop
remainder function for general kinematics, up to 113 constants. Taking its
multi-Regge limit and matching to our four-loop LLA and NLLA results, we fix
all but one of the constants that survive in this limit. The multi-Regge limit
factorizes in the variables (\nu,n) which are related to (w,w*) by a
Fourier-Mellin transform. We can transform the single-valued harmonic
polylogarithms to functions of (\nu,n) that incorporate harmonic sums,
systematically through transcendental weight six. Combining this information
with the four-loop results, we determine the eigenvalues of the BFKL kernel in
the adjoint representation to NNLLA accuracy, and the MHV product of impact
factors to NNNLLA accuracy, up to constants representing beyond-the-symbol
terms and the one symbol-level constant. Remarkably, only derivatives of the
polygamma function enter these results. Finally, the LLA approximation to the
six-gluon NMHV amplitude is evaluated through ten loops.Comment: 71 pages, 2 figures, plus 10 ancillary files containing analytic
expressions in Mathematica format. V2: Typos corrected and references added.
V3: Typos corrected; assumption about single-Reggeon exchange made explici
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The use of phylogeny to interpret cross-cultural patterns in plant use and guide medicinal plant discovery: an example from Pterocarpus (Leguminosae)
The study of traditional knowledge of medicinal plants has led to discoveries that have helped combat diseases and improve healthcare. However, the development of quantitative measures that can assist our quest for new medicinal plants has not greatly advanced in recent years. Phylogenetic tools have entered many scientific fields in the last two decades to provide explanatory power, but have been overlooked in ethnomedicinal studies. Several studies show that medicinal properties are not randomly distributed in plant phylogenies, suggesting that phylogeny shapes ethnobotanical use. Nevertheless, empirical studies that explicitly combine ethnobotanical and phylogenetic information are scarce.In this study, we borrowed tools from community ecology phylogenetics to quantify significance of phylogenetic signal in medicinal properties in plants and identify nodes on phylogenies with high bioscreening potential. To do this, we produced an ethnomedicinal review from extensive literature research and a multi-locus phylogenetic hypothesis for the pantropical genus Pterocarpus (Leguminosae: Papilionoideae). We demonstrate that species used to treat a certain conditions, such as malaria, are significantly phylogenetically clumped and we highlight nodes in the phylogeny that are significantly overabundant in species used to treat certain conditions. These cross-cultural patterns in ethnomedicinal usage in Pterocarpus are interpreted in the light of phylogenetic relationships.This study provides techniques that enable the application of phylogenies in bioscreening, but also sheds light on the processes that shape cross-cultural ethnomedicinal patterns. This community phylogenetic approach demonstrates that similar ethnobotanical uses can arise in parallel in different areas where related plants are available. With a vast amount of ethnomedicinal and phylogenetic information available, we predict that this field, after further refinement of the techniques, will expand into similar research areas, such as pest management or the search for bioactive plant-based compounds
Strong interface-induced spin-orbit coupling in graphene on WS2
Interfacial interactions allow the electronic properties of graphene to be
modified, as recently demonstrated by the appearance of satellite Dirac cones
in the band structure of graphene on hexagonal boron nitride (hBN) substrates.
Ongoing research strives to explore interfacial interactions in a broader class
of materials in order to engineer targeted electronic properties. Here we show
that at an interface with a tungsten disulfide (WS2) substrate, the strength of
the spin-orbit interaction (SOI) in graphene is very strongly enhanced. The
induced SOI leads to a pronounced low-temperature weak anti-localization (WAL)
effect, from which we determine the spin-relaxation time. We find that
spin-relaxation time in graphene is two-to-three orders of magnitude smaller on
WS2 than on SiO2 or hBN, and that it is comparable to the intervalley
scattering time. To interpret our findings we have performed first-principle
electronic structure calculations, which both confirm that carriers in
graphene-on-WS2 experience a strong SOI and allow us to extract a
spin-dependent low-energy effective Hamiltonian. Our analysis further shows
that the use of WS2 substrates opens a possible new route to access topological
states of matter in graphene-based systems.Comment: Originally submitted version in compliance with editorial guidelines.
Final version with expanded discussion of the relation between theory and
experiments to be published in Nature Communication
Convergent genetic linkage and associations to language, speech and reading measures in families of probands with Specific Language Impairment
We analyzed genetic linkage and association of measures of language, speech and reading phenotypes to candidate regions in a single set of families ascertained for SLI. Sib-pair and family-based analyses were carried out for candidate gene loci for Reading Disability (RD) on chromosomes 1p36, 3p12-q13, 6p22, and 15q21, and the speech-language candidate region on 7q31 in a sample of 322 participants ascertained for Specific Language Impairment (SLI). Replication or suggestive replication of linkage was obtained in all of these regions, but the evidence suggests that the genetic influences may not be identical for the three domains. In particular, linkage analysis replicated the influence of genes on chromosome 6p for all three domains, but association analysis indicated that only one of the candidate genes for reading disability, KIAA0319, had a strong effect on language phenotypes. The findings are consistent with a multiple gene model of the comorbidity between language impairments and reading disability and have implications for neurocognitive developmental models and maturational processes
Wordless intervention for epilepsy in learning disabilities (WIELD):study protocol for a randomized controlled feasibility trial
Epilepsy is the most common neurological problem that affects people with learning disabilities. The high seizure frequency, resistance to treatments, associated skills deficit and co-morbidities make the management of epilepsy particularly challenging for people with learning disabilities. The Books Beyond Words booklet for epilepsy uses images to help people with learning disabilities manage their condition and improve quality of life. Our aim is to conduct a randomized controlled feasibility trial exploring key methodological, design and acceptability issues, in order to subsequently undertake a large-scale randomized controlled trial of the Books Beyond Words booklet for epilepsy
A53T-alpha-synuclein-overexpression in the mouse nigrostriatal pathway leads to early increase of 14-3-3 epsilon and late increase of GFAP
Parkinson’s disease (PD) is a neurodegenerative disorder frequent at old age characterized by atrophy of the nigrostriatal projection. Overexpression and A53T-mutation of the presynaptic, vesicle-associated chaperone alpha-synuclein are known to cause early-onset autosomal dominant PD. We previously generated mice with transgenic overexpression of human A53T-alpha-synuclein (A53T-SNCA) in dopaminergic substantia nigra neurons as a model of early PD. To elucidate the early and late effects of A53T-alpha-synuclein on the proteome of dopaminergic nerve terminals in the striatum, we now investigated expression profiles of young and old mice using two-dimensional fluorescence difference in gel electrophoresis (2D-DIGE) and mass spectrometry. In total, 15 proteins were upregulated and 2 downregulated. Mice before the onset of motor anomalies showed an upregulation of the spot containing 14-3-3 proteins, in particular the epsilon isoform, as well as altered levels of chaperones, vesicle trafficking and bioenergetics proteins. In old mice, the persistent upregulation of 14-3-3 proteins was aggravated by an increase of glial fibrillary acidic protein (GFAP) suggesting astrogliosis due to initial neurodegeneration. Independent immunoblots corroborated GFAP upregulation and 14-3-3 upregulation for the epsilon isoform, and also detected significant eta and gamma changes. Only for 14-3-3 epsilon a corresponding mRNA increase was observed in midbrain, suggesting it is transcribed in dopaminergic perikarya and accumulates as protein in presynapses, together with A53T-SNCA. 14-3-3 proteins associate with alpha-synuclein in vitro and in pathognomonic Lewy bodies of PD brains. They act as chaperones in signaling, dopamine synthesis and stress response. Thus, their early dysregulation probably reflects a response to alpha-synuclein toxicity
Plant DNA barcodes and assessment of phylogenetic community structure of a tropical mixed dipterocarp forest in Brunei Darussalam (Borneo)
DNA barcoding is a fast and reliable tool to assess and monitor biodiversity and, via community phylogenetics, to investigate ecological and evolutionary processes that may be responsible for the community structure of forests. In this study, DNA barcodes for the two widely used plastid coding regions rbcL and matK are used to contribute to identification of morphologically undetermined individuals, as well as to investigate phylogenetic structure of tree communities in 70 subplots (10 × 10m) of a 25-ha forest-dynamics plot in Brunei (Borneo, Southeast Asia). The combined matrix (rbcL + matK) comprised 555 haplotypes (from ≥154 genera, 68 families and 25 orders sensu APG, Angiosperm Phylogeny Group, 2016), making a substantial contribution to tree barcode sequences from Southeast Asia. Barcode sequences were used to reconstruct phylogenetic relationships using maximum likelihood, both with and without constraining the topology of taxonomic orders to match that proposed by the Angiosperm Phylogeny Group. A third phylogenetic tree was reconstructed using the program Phylomatic to investigate the influence of phylogenetic resolution on results. Detection of non-random patterns of community assembly was determined by net relatedness index (NRI) and nearest taxon index (NTI). In most cases, community assembly was either random or phylogenetically clustered, which likely indicates the importance to community structure of habitat filtering based on phylogenetically correlated traits in determining community structure. Different phylogenetic trees gave similar overall results, but the Phylomatic tree produced greater variation across plots for NRI and NTI values, presumably due to noise introduced by using an unresolved phylogenetic tree. Our results suggest that using a DNA barcode tree has benefits over the traditionally used Phylomatic approach by increasing precision and accuracy and allowing the incorporation of taxonomically unidentified individuals into analyses
Evidence for widespread hydrated minerals on asteroid (101955) Bennu
Early spectral data from the Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer (OSIRIS-REx) mission reveal evidence for abundant hydrated minerals on the surface of near-Earth asteroid (101955) Bennu in the form of a near-infrared absorption near 2.7 µm and thermal infrared spectral features that are most similar to those of aqueously altered CM-type carbonaceous chondrites. We observe these spectral features across the surface of Bennu, and there is no evidence of substantial rotational variability at the spatial scales of tens to hundreds of metres observed to date. In the visible and near-infrared (0.4 to 2.4 µm) Bennu’s spectrum appears featureless and with a blue (negative) slope, confirming previous ground-based observations. Bennu may represent a class of objects that could have brought volatiles and organic chemistry to Earth
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