170,423 research outputs found
Status and ecology of the Priolo or Azores bullfinch, Pyrrhula murina
No full textI studied the seasonal variation in habitat selection, diet, food supply and food selection of the Priolo or Azores bullfinch, Pyrrhula murina. This species and its associated habitat, the Azorean native cloud forest, are poorly known and are threatened by afforestation and the invasion of exotic flora. In addition detailed studies of these aspects are lacking for oceanic island birds. Throughout this study a comparison between the ecology of the Priolo and that of mainland Bullfinches is made. The primary aims of this study were (1) to evaluate the importance of three alternative hypotheses in explaining the present distribution and abundance of this bird: habitat structure and composition, food availability and food preference, and (2) propose management strategies. Point-counts and capture-recapture indicate a population of 60 to 200 pairs. The bird breeds from mid-June to late August. Annual mortality was in the order of 45-50%. Stations were marked every 200 m along tracks covering all vegetation types in the area. These were walked three times a month to record presence or absence of birds per habitat type. The habitat structure and vegetation composition were recorded at these stations and used to explain the number of times a bird was detected at stations using logistic modelling. Diet was assessed from observations of feeding birds and faecal analysis. Food supply was examined from quadrats placed systematically within foraging habitats and from marked plots of winter food stocks. Food preferences were examined by comparing (a) availability and usage of foods in the field, (b) selected and rejected food items and (c) using food choice trials with captive birds. TTie importance of seed phenolics in explaining patterns of preferences for species and individual trees in winter was examined. The distribution of the Priolo was highly associated with native vegetation and its margins all year round. Other habitats were of marginal importance.The precision of habitat selectivity increased in the following direction: summer The diet ranged from invertebrates and herbaceous seeds in summer, to seeds of fleshy fruits in autumn, fern sporangia and tree seeds (of Clethra arborea) in winter and, flower buds, fern fronds and moss tips in spring. Introduced species were very important in the diet but in August/September and in April native species were significantly more important. In April, birds were highly dependent on flower buds of Ilex perado. At this time, the abundance of seeds and sporangia was at its lowest. An experiment with enclosures showed that the Priolo foraging pressure significantly reduced the number of flower buds. Food preferences changed throughout the year and seemed a complex function of availability, size, palatability and accessibility of foods. Seeds of fleshy fruits were preferred to those of C. arborea. Seeds of C. arborea were ignored when flower buds reached a length of 2.8-3.0 mm. In autumn, C. arborea was preferred to sporangia of large ferns, but in spring the birds showed the opposite behaviour. Priolos also showed preference for larger items of most winter foods. Phenolic compounds did not explain C. arborea tree preference nor why birds switched from seeds to flower buds in spring. Within a small resource spectrum birds should be less discriminating and energy may be the most important factor in food selection. Overall, the data suggested that a food supply hypothesis was better in explaining patterns of Priolo distribution and abundance than a habitat structure hypothesis but food preference is important for a full understanding of this question. A shortage of preferred foods may occur in late winter. Other available foods may be inadequate. Some implications for the limitation of this population are discussed. The Priolo needs the several mosaics of the native forest to complete its annual cycle. Nowadays, the mature forest mosaic seems to be the least abundant. In terms of conservation it is necessary to control the expansion of exotic plants and, restore and enlarge the area of native forest. It seems especially important to increase the population of flower-bud producing species
Static and Fatigue Behaviour of Stitched Graphite/Epoxy Composite Laminates
No full textThe paper studies the effect of edge stitching on tensile static and fatigue properties of graphite fiber reinforced laminates. The influence of Kevlar stitchings on edge delaminations, ultimate tensile strength and tension-tension fatigue life were examined on laminates of two stacking sequences ([±45/0/90]s and [±30/90]s), as representative of two classes of fiber-dominated and matrix-dominated laminates. Through-thickness stitching offered a significant improvement in the static delamination resistance of laminated composites, but had varying effects on the ultimate tensile stress of the laminates under study, with an increase in strength of [±30/90]s laminates and a decrease in strength of [±45/0/90]s laminates. Similarly the fatigue life of matrix dominated [±30/90]s specimens was considerably extended by stitching, while the fatigue resistance of fiber-dominated [±45/0/90]s specimens was reduced, particularly at high fatigue stresses. Stitching appeared very efficient in arresting delamination in [±30/90]s specimens for both static and fatigue loads, but did not prove to be as efficient in stopping fatigue delaminations in [±45/0/90]s specimens, since Kevlar threads were found to be prone to breakage under cyclic loading. As a conclusion, while the static delamination resistance of laminated composites is improved by stitching, this does not automatically result in better fatigue performance for all lamination sequences
Modelling of ground motion in the vicinity of massive structures
No full textA two-dimensional elastic Chebyshev spectral element method (SPEM) is used to model the seismic wavefield within a massive structure and in its vicinity. We consider 2-D models where a linear elastic structure, with quadrangular cross-section, resting on an elastic homogeneous half-space, is impinged upon by the waves generated by a surface impulse at some distance. The scattering of Rayleigh waves and the response of the structure are extensively analysed in a parametric way, varying size, mechanical parameters and shape of the load. Some of the models considered are representative of embankments and earth dams. The simulation shows that some models resonate, storing part of the incoming energy. With realistic parameters, the lowest resonance frequency is due to pure shear deformation and is controlled by the shear velocity and height of the load. Flexural modes are excited only at higher frequencies. The acceleration at the top of the structure may be five/seven times higher than at the base, depending on the mass of the structure. The gradual release of trapped energy produces a ground roll lasting several seconds after the wave front has passed. The ground-roll amplitude depends on the sturcture's mass and can be as large as 30% of the peak acceleration. Outside resonance conditions, the ground motion is almost unaffected by the presence of the artefact; the horizontal motion on top of it is nearly twice the motion at ground level. Similar results should be expected when the incident field is an upcoming shear wave. A qualitative discussion shows that the presence of anelastic attenuation in the embankment does not significantly alter the preceding conclusions, unless it is of very low values (e.g. Q < 15). The modelling results that we discuss indicate that the soil-structure interaction may substantially alter the 'free-field' ground motion. From a practical point of view, the main conclusions are: (1) careful analysis is necessary when interpreting seismic records collected in the vicinity of large artefacts; (2) seismic hazard at a site may depend on the presence of man-made structures such as embankments, dams, tall and massive buildings
Caratterizzazione della risposta all'impatto di laminati cross-ply con cuciture di rinforzo
No full text
Fluorine in Ge: Segregation and EOR-defects stabilization
No full textIn this paper we investigate the F behavior in Ge during solid phase epitaxy (SPE) and post-SPE annealing. Fluorine implanted with a fluence of 1 x 10(15) F/cm(2) and an energy of 35 key induced the formation of an amorphous Ge layer. Detailed chemical and structural characterizations of the as implanted and annealed samples evidenced a strong segregation of F at the moving amorphous/crystalline interface, leading to a remarkable SPE rate retardation. In addition, we observed that F accumulates in correspondence of the end of range (EOR) defects. The comparison between the thermal evolution of damage produced by self-implantation and F implantation in Ge suggests that F increases significantly the stability of EOR. Such behavior clarifies the role of F in modifying the As diffusion in Ge recently reported in literature. (C) 2011 Elsevier B.V. All rights reserved
Policies to clean up toxic industrial contaminated sites of Gela and Priolo: a cost-benefit analysis.
No full textBACKGROUND: Cost-benefit analysis is a transparent tool to inform policy makers about the potential effect of regulatory interventions, nevertheless its use to evaluate clean-up interventions in polluted industrial sites is limited. The two industrial areas of Gela and Priolo in Italy were declared "at high risk of environmental crisis" in 1990. Since then little has been done to clean the polluted sites and reduce the health outcomes attributable to pollution exposure. This study, aims to quantify the monetary benefits resulting from clean-up interventions in the contaminated sites of Gela and Priolo. METHODS: A damage function approach was used to estimate the number of health outcomes attributable to industrial pollution exposure. Extensive one way analyses and probabilistic analyses were conducted to investigate the sensitivity of results to different model assumptions. RESULTS: It has been estimated that, on average, 47 cases of premature death, 281 cases of cancer and 2,702 cases of non-cancer hospital admission could be avoided each year by removing environmental exposure in these two areas. Assuming a 20 year cessation lag and a 4% discount rate we calculate that the potential monetary benefit of removing industrial pollution is €3,592 million in Priolo and €6,639 million in Gela. CONCLUSIONS: Given the annual number of health outcomes attributable to pollution exposure the effective clean-up of Gela and Priolo should be prioritised. This study suggests that clean-up policies costing up to €6,639 million in Gela and €3,592 million in Priolo would be cost beneficial. These two amounts are notably higher than the funds allocated thus far to clean up the two sites, €127.4 million in Gela and €774.5 million in Priolo, implying that further economic investments - even considerable ones - could still prove cost beneficial
Status and ecology of the Priolo or Azores bullfinch, Pyrrhula murina
No full textI studied the seasonal variation in habitat selection, diet, food supply and food
selection of the Priolo or Azores bullfinch, Pyrrhula murina. This species and its associated
habitat, the Azorean native cloud forest, are poorly known and are threatened by
afforestation and the invasion of exotic flora. In addition detailed studies of these aspects
are lacking for oceanic island birds. Throughout this study a comparison between the
ecology of the Priolo and that of mainland Bullfinches is made. The primary aims of this
study were (1) to evaluate the importance of three alternative hypotheses in explaining the
present distribution and abundance of this bird: habitat structure and composition, food
availability and food preference, and (2) propose management strategies.
Point-counts and capture-recapture indicate a population of 60 to 200 pairs. The
bird breeds from mid-June to late August. Annual mortality was in the order of 45-50%.
Stations were marked every 200 m along tracks covering all vegetation types in the
area. These were walked three times a month to record presence or absence of birds per
habitat type. The habitat structure and vegetation composition were recorded at these
stations and used to explain the number of times a bird was detected at stations using
logistic modelling. Diet was assessed from observations of feeding birds and faecal
analysis. Food supply was examined from quadrats placed systematically within foraging
habitats and from marked plots of winter food stocks. Food preferences were examined by
comparing (a) availability and usage of foods in the field, (b) selected and rejected food
items and (c) using food choice trials with captive birds. TTie importance of seed phenolics
in explaining patterns of preferences for species and individual trees in winter was
examined.
The distribution of the Priolo was highly associated with native vegetation and its
margins all year round. Other habitats were of marginal importance.The precision of habitat
selectivity increased in the following direction: summer
The diet ranged from invertebrates and herbaceous seeds in summer, to seeds of
fleshy fruits in autumn, fern sporangia and tree seeds (of Clethra arborea) in winter and,
flower buds, fern fronds and moss tips in spring. Introduced species were very important
in the diet but in August/September and in April native species were significantly more
important. In April, birds were highly dependent on flower buds of Ilex perado. At this
time, the abundance of seeds and sporangia was at its lowest. An experiment with
enclosures showed that the Priolo foraging pressure significantly reduced the number of
flower buds.
Food preferences changed throughout the year and seemed a complex function of
availability, size, palatability and accessibility of foods. Seeds of fleshy fruits were
preferred to those of C. arborea. Seeds of C. arborea were ignored when flower buds
reached a length of 2.8-3.0 mm. In autumn, C. arborea was preferred to sporangia of large
ferns, but in spring the birds showed the opposite behaviour. Priolos also showed
preference for larger items of most winter foods. Phenolic compounds did not explain C.
arborea tree preference nor why birds switched from seeds to flower buds in spring.
Within a small resource spectrum birds should be less discriminating and energy may be
the most important factor in food selection.
Overall, the data suggested that a food supply hypothesis was better in explaining
patterns of Priolo distribution and abundance than a habitat structure hypothesis but food
preference is important for a full understanding of this question. A shortage of preferred
foods may occur in late winter. Other available foods may be inadequate. Some
implications for the limitation of this population are discussed. The Priolo needs the several
mosaics of the native forest to complete its annual cycle. Nowadays, the mature forest
mosaic seems to be the least abundant. In terms of conservation it is necessary to control
the expansion of exotic plants and, restore and enlarge the area of native forest. It seems
especially important to increase the population of flower-bud producing species.</p
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