1,393 research outputs found
Chemical composition of barks from Quercus faginea trees and characterization of their lipophilic and polar extracts
The bark from Quercus faginea mature trees from two sites was chemically characterized for the first time. The barks showed the
following composition: ash 14.6%, total extractives 13.2%, suberin 2.9% and lignin 28.2%. The polysaccharides were composed
mainly of glucose and xylose (50.3% and 35.1% of all monosaccharides respectively) with 4.8% of uronic acids. The suberin
composition was: ω-hydroxyacids 46.3% of total compounds, ɑ,ω-alkanoic diacids 22.3%, alkanoic acids 5.9%, alkanols 6.7% and
aromatics 6.9% (ferulic acid 4.0%). Polar extracts (ethanol-water) had a high phenolic content of 630.3 mg of gallic acid equivalents
(GAE)/g of extract, condensed tannins 220.7 mg of catechin equivalents (CE)/g extract, and flavonoids 207.7 mg CE/g of extract.
The antioxidant activity was very high corresponding to 1567 mg Trolox equivalents/g of extract, and an IC50 of 2.63 μg extract/ml.
The lipophilic extracts were constituted mainly by glycerol and its derivatives (12.3% of all compounds), alkanoic acids (27.8%),
sterols (11.5%) and triterpenes (17.8%). In view of an integrated valorization, Quercus faginea barks are interesting sources of
polar compounds including phenols and polyphenols with possible interesting bioactivities, while the sterols and triterpenes
contained in the lipophilic extracts are also valuable bioactive compounds or chemical intermediates for specific high-value market
niches, such as cosmetics, pharmaceuticals and biomedicineinfo:eu-repo/semantics/publishedVersio
Quercus rotundifolia bark as a source of polar extracts: structural and chemical characterization
Quercus rotundifolia bark was studied regarding anatomical, chemical, and antioxidant
properties from trees in two sites in southern Portugal and are here reported for the first time. The
general structure and anatomy of Q. rotundifolia bark showed a rhytidome with sequential undulated
and anastomosed periderms with a small proportion of cork, while the phloem included broad rays
with strong cell sclerification, groups of sclereids with embed large prismatic crystals, and abundant
druses in parenchyma cells. The mean chemical composition was 15.5% ash, 1.6% dichloromethane
extractives, 6.4% ethanol and 9.3% water extractives, 3.0% suberin, 30.5% total lignin, and 33.8%
carbohydrates. Carbohydrates included mainly glucose (50.7% of total monomers) and xylose
(23.8%), with uronic (3.0%) and acetic acids (1.0%). Suberin was mainly composed of !-hydroxyacids
(48.0% of all compounds) and ,!-diacids (19.5%). The main compounds found in the lipophilic
extracts were triterpenes (43.6%–56.2% of all compounds) and alkanoic acids (32.7%–41.7%). Phenolic
content was high especially in the ethanol extracts, ranging from 219.5–572.9 mg GAE/g extract and
comprising 162.5–247.5 CE/g extract of flavonoids and 41.2–294.1 CE/g extract of condensed tannins.
The extracts revealed very good antioxidant properties with IC50 values of 4.4 g ethanol extract/mL
and 4.7 g water extract/mL. Similar anatomical, chemical, and antioxidant characteristics were
found in the bark from both sites. The high phenolic content and excellent antioxidant characteristics
of polar extracts showed holm oak barks to be a promising natural source of antioxidants with
possible use in industry and pharmaceutical/medical areasinfo:eu-repo/semantics/publishedVersio
Anomalous tag diffusion in the asymmetric exclusion model with particles of arbitrary sizes
Anomalous behavior of correlation functions of tagged particles are studied
in generalizations of the one dimensional asymmetric exclusion problem. In
these generalized models the range of the hard-core interactions are changed
and the restriction of relative ordering of the particles is partially brocken.
The models probing these effects are those of biased diffusion of particles
having size S=0,1,2,..., or an effective negative "size" S=-1,-2,..., in units
of lattice space. Our numerical simulations show that irrespective of the range
of the hard-core potential, as long some relative ordering of particles are
kept, we find suitable sliding-tag correlation functions whose fluctuations
growth with time anomalously slow (), when compared with the normal
diffusive behavior (). These results indicate that the critical
behavior of these stochastic models are in the Kardar-Parisi-Zhang (KPZ)
universality class. Moreover a previous Bethe-ansatz calculation of the
dynamical critical exponent , for size particles is extended to
the case and the KPZ result is predicted for all values of .Comment: 4 pages, 3 figure
Impacts of deforestation on plant-pollinator networks assessed using an agent based model.
Plant-pollinator networks have been widely used to understand the ecology of mutualistic interactions between plants and animals. While a number of general patterns have been identified, the mechanisms underlying the structure of plant-pollinator networks are poorly understood. Here we present an agent based model (ABM) that simulates the movement of bees over heterogeneous landscapes and captures pollination events, enabling the influence of landscape pattern on pollination networks to be explored. Using the model, we conducted a series of experiments using virtual landscapes representing a gradient of forest loss and fragmentation. The ABM was able to produce expected trends in network structure, from simulations of interactions between individual plants and pollinators. For example, results indicated an increase in the index of complementary specialization (H2') and a decline in network connectance with increasing forest cover. Furthermore, network nestedness was not associated with the degree of forest cover, but was positively related to forest patch size, further supporting results obtained in the field. This illustrates the potential value of ABMs for exploring the structure and dynamics of plant-pollinator networks, and for understanding the mechanisms that underlie them. We attribute the results obtained primarily to a shift from specialist to generalist pollinators with increasing forest loss, a trend that has been observed in some field situations
Harbor porpoise losing its edge:Genetic time series suggests a rapid population decline in Iberian waters over the last 30 years
Impact of climate change is expected to be especially noticeable at the edges of a species' distribution, where they meet suboptimal habitat conditions. In Mauritania and Iberia, two genetically differentiated populations of harbor porpoises (Phocoena phocoena) form an ecotype adapted to local upwelling conditions and distinct from other ecotypes further north on the NE Atlantic continental shelf and in the Black Sea. By analyzing the evolution of mitochondrial genetic variation in the Iberian population between two temporal cohorts (1990–2002 vs. 2012–2015), we report a substantial decrease in genetic diversity. Phylogenetic analyses including neighboring populations identified two porpoises in southern Iberia carrying a divergent haplotype closely related to those from the Mauritanian population, yet forming a distinct lineage. This suggests that Iberian porpoises may not be as isolated as previously thought, indicating possible dispersion from Mauritania or an unknown population in between, but none from the northern ecotype. Demo-genetic scenario testing by approximate Bayesian computation showed that the rapid decline in the Iberian mitochondrial diversity was not simply due to the genetic drift of a small population, but models support instead a substantial decline in effective population size, possibly resulting from environmental stochasticity, prey depletion, or acute fishery bycatches. These results illustrate the value of genetics time series to inform demographic trends and emphasize the urgent need for conservation measures to ensure the viability of this small harbor porpoise population in Iberian waters.</p
Sub-Bandgap Sensitization of Perovskite Semiconductors via Colloidal Quantum Dots Incorporation
ABSTRACT: By taking advantage of the outstanding intrinsic optoelectronic properties of perovskite-based photovoltaic materials, together with the strong near-infrared (NIR) absorption and electronic confinement in PbS quantum dots (QDs), sub-bandgap photocurrent generation is possible, opening the way for solar cell efficiencies surpassing the classical limits. The present study shows an effective methodology for the inclusion of high densities of colloidal PbS QDs in a MAPbI3 (methylammonium lead iodide) perovskite matrix as a means to enhance the spectral window of photon absorption of the perovskite host film and allow photocurrent production below its bandgap. The QDs were introduced in the perovskite matrix in different sizes and concentrations to study the formation of quantum-confined levels within the host bandgap and the potential formation of a delocalized intermediate mini-band (IB). Pronounced sub-bandgap (in NIR) absorption was optically confirmed with the introduction of QDs in the perovskite. The consequent photocurrent generation was demonstrated via photoconductivity measurements, which indicated IB establishment in the films. Despite verifying the reduced crystallinity of the MAPbI3 matrix with a higher concentration and size of the embedded QDs, the nanostructured films showed pronounced enhancement (above 10-fold) in NIR absorption and consequent photocurrent generation at photon energies below the perovskite bandgap.info:eu-repo/semantics/publishedVersio
Ideal Spin Filters: Theoretical Study of Electron Transmission Through Ordered and Disordered Interfaces Between Ferromagnetic Metals and Semiconductors
It is predicted that certain atomically ordered interfaces between some
ferromagnetic metals (F) and semiconductors (S) should act as ideal spin
filters that transmit electrons only from the majority spin bands or only from
the minority spin bands of the F to the S at the Fermi energy, even for F with
both majority and minority bands at the Fermi level. Criteria for determining
which combinations of F, S and interface should be ideal spin filters are
formulated. The criteria depend only on the bulk band structures of the S and F
and on the translational symmetries of the S, F and interface. Several examples
of systems that meet these criteria to a high degree of precision are
identified. Disordered interfaces between F and S are also studied and it is
found that intermixing between the S and F can result in interfaces with spin
anti-filtering properties, the transmitted electrons being much less spin
polarized than those in the ferromagnetic metal at the Fermi energy. A patent
application based on this work has been commenced by Simon Fraser University.Comment: RevTeX, 12 pages, 5 figure
Recombinant Biglycan Promotes Bone Morphogenetic Protein-induced Osteogenesis
The aim of this study was to determine the effects of glutathione-S-transferase-fused recombinant biglycan (GST-BGN) on craniofacial bone regeneration. We recently demonstrated a positive effect of tissue-derived BGN on bone morphogenetic protein 2 (BMP-2) function, which is exerted likely via the BGN core protein. Here, we investigated the effects of GST-BGN lacking any posttranslational modifications on BMP-2 function in vitro and in vivo. In the C2C12 cell culture system, BMP-2-induced Smad 1/5/8 phosphorylation and alkaline phosphatase activity were both enhanced by the addition of GST-BGN. For the in vivo effect, we employed a Sprague-Dawley rat mandible defect model utilizing 1 µg (optimal) or 0.1 µg (suboptimal) of BMP-2 combined with 0, 2, 4, or 8 µg of GST-BGN. At 2 weeks post-surgery, newly formed bone was evaluated by microcomputed tomography and histologic analyses. The results revealed that the greatest amounts of bone within the defect were formed in the groups of suboptimal BMP-2 combined with 4 or 8 µg of GST-BGN. Also, bone was well organized versus that formed by the optimal dose of BMP. These results indicate that recombinant BGN is an efficient substrate to promote low-dose BMP-induced osteogenesis
Forest and connectivity loss simplify tropical pollination networks
Mutualistic interactions between plants and pollinators play an essential role in the organization and persistence of biodiversity. The structure of interaction networks mediates the resilience of local communities and ecosystem functioning to environmental changes. Hence, network structure conservation may be more critical for maintaining biodiversity and ecological services than the preservation of isolated species in changing landscapes. Here, we intensively surveyed seven 36 km(2) landscapes to empirically investigate the effects of forest loss and landscape configuration on the structure of plant-pollinator networks in understory vegetation of Brazilian Atlantic Forest. Our results indicate that forest loss and isolation affect the structure of the plant-pollinator networks, which were smaller in deforested landscapes, and less specialized as patch isolation increased. Lower nestedness and degree of specialization (HMODIFIER LETTER PRIME2) indicated that the remaining plant and bee species tend to be generalists, and many of the expected specialized interactions in the network were already lost. Because generalist species generate a cohesive interaction core in these networks, these simplified networks might be resistant to loss of peripheral species, but may be susceptible to the extinction of the most generalist species. We suggest that such a network pattern is an outcome of landscapes with a few remaining isolated patches of natural habitat. Our results add a new perspective to studies of plant-pollinator networks in fragmented landscapes, showing that those interaction networks might also be used to indicate how changes in natural habitat affect biodiversity and biotic interactions.Environmental Biolog
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