499 research outputs found
Anagallis monelli
No full textFoglio dell\u27erbario di Giovanni Marsili con cartellino manoscritto: Anagallis monelli?
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Famiglia: Primulaceae1 ramo fiorifero su foglio cartace
Breeding system studies with three species of Anagallis (Primulaceae): Self-incompatibility and reduced female fertility in A-monelli L.
No full textThe pollination biology, Fruit set and breeding system of Anagallis arvensis. A. parviflora and A. monelii were studied in the field and glasshouse. No pollinators were observed at flowers of A. arvensis and A. parviflora, and hand pollinations indicated that these species are self-compatible taxa which automatically self-pollinate as the petals close at the end of the first day. Flowers of A. monelli were visited by several small halictid bee pollinators and a field diallel with seven plants indicated that this species is self-incompatible. Fruit set in A. monelli is correlated with distance to the nearest conspecific neighbour such that beyond 2 m fruit set is relatively low. The diallel cross, and also an analysis or the number of seeds per capsule for all plants located within 2 m of a conspecific. indicated that about 18% of the population of A. monelli showed low female fecundity and were thus 'male dominant' individuals. (C) 2001 Annals of Botany Company.</p
Breeding system studies with three species of Anagallis (Primulaceae): Self-incompatibility and reduced female fertility in A-monelli L.
No full textThe pollination biology, Fruit set and breeding system of Anagallis arvensis. A. parviflora and A. monelii were studied in the field and glasshouse. No pollinators were observed at flowers of A. arvensis and A. parviflora, and hand pollinations indicated that these species are self-compatible taxa which automatically self-pollinate as the petals close at the end of the first day. Flowers of A. monelli were visited by several small halictid bee pollinators and a field diallel with seven plants indicated that this species is self-incompatible. Fruit set in A. monelli is correlated with distance to the nearest conspecific neighbour such that beyond 2 m fruit set is relatively low. The diallel cross, and also an analysis or the number of seeds per capsule for all plants located within 2 m of a conspecific. indicated that about 18% of the population of A. monelli showed low female fecundity and were thus 'male dominant' individuals. (C) 2001 Annals of Botany Company.</p
Plain fatigue resistance of shot peened high strength aluminium alloys: Effects of loading ratio
No full textThe effect of different shot-peening treatments on the reverse and pulsating bending fatigue behaviour of Al 7075 T651 was studied. The fatigue improvements with respect to the unpeened condition and the influence of the peening intensity on fatigue were discussed accounting for the effects of surface modifications and residual stresses. In particular, the extent of the residual stress redistribution during loading was investigated by means of X-ray diffraction (XRD) measurements. No significant residual stress relaxation was observed in samples tested to a load level corresponding to the fatigue endurance at 5x10^6 cycles. Residual stress relaxation was observed only when the material plastic flow stress was achieved during the compressive part of the fatigue load cycle. Accordingly, shot peened samples with deep sub-superficial compressive residual stress peak showed a reversed fatigue endurance level corresponding to the condition of incipient plastic flow. This phenomenon was also accompanied by sub-superficial fatigue crack initiation. On the contrary, samples tested at shorter fatigue lives or under pulsating loading conditions showed crack initiation close to the surface. The initial and the stabilised residual stress profiles were considered for discussing the improvement in the fatigue behaviour due to peening. For this purpose, a multiaxial fatigue criterion was adopted to account for the biaxial residual stress field. The fatigue life was quite accurately predicted as long as fatigue initiation occurs on the surface
Elasto-plastic behavior of a Warrington-Seale rope: Experimental analysis and finite element modeling
No full textThe mechanical behavior of Warrington-Seale (WS) strands as well as of a Warrington Seale rope with a polymeric fiber core is investigated. Specifically, the elasto-plastic response under axial loading conditions beyond the elastic limit is studied. Tensile tests were carried out on both WS strands and ropes. The strain-stress curves of single wires with different diameters were determined and used as input of a fully parametric Finite Element (FE) study aimed at investigating the stress and strain evolution in the rope in the elastic as well as in the elasto-platic regime. The numerical simulations, validated on the basis of the experimental results, are useful to shed light on the way the load is distributed among the wires. The different damage evolution and the most likely failure mechanisms of strands and of ropes were identified. Helpful remarks are drawn about the structural response of these components under heavy loading conditions
Fatigue crack kinking in high strength aluminium alloys: the effect of loading direction, notch geometry and microstructure texture
No full textNumerical simulation of residual stress relaxation in shot peened high-strength aluminum alloys under reverse bending fatigue
No full textThe mechanism of the residual stress relaxation during the fatigue life of shot peened high-strength aluminum alloys was investigated. Experiments were conducted on speci-mens subjected to three different shot peening treatments and tested under reverse bend-ing fatigue. x-ray diffraction (XRD) measurements were carried out to determine the initial and stabilized residual stress fields. The residual stress field created by the surface treatments has been introduced into a finite element (FE) model by means of a fictitious temperature distribution. The elastic-plastic response of the superficial layers affected by the shot peening treatments has been derived through reverse strain axial testing com-bined with microhardness tests and implemented in the FE model. The proposed numerical/experimental approach is able to satisfactorily predict the residual stress field evolution. Notably, relaxation has been correctly simulated in the low-cycle fatigue regime and imputed to plastic flow in compression when the superposition of compressive residual and bending stresses exceeds the local cyclic yield strength of the material. Conversely, the residual stress field remains stable at load levels corresponding to the 5x10^6 cycles fatigue endurance
Genetic control of self-incompatibility in Anagallis monelli (Primulaceae: Myrsinaceae)
No full textThe genetic control of self-incompatibility (SI) was studied in the Mediterranean short-lived perennial species Anagallis monelli (Primulaceae: Myrsinaccae). Arrays of siblings, including families derived from reciprocal crosses, were cross-pollinated in full diallels, and compatibility groups were assesssed from a census or fruit-set. Two, three and four intercompatible and intraincompatible groups were found. These crossing relationships fit the model for gametophytic SI controlled by a single polymorphic gene locus in families derived from parents with one or no S alleles in common (two vs. four compatibility groups), whilst one genotype was presumed to be missing in the small families that showed only three compatibility groups.</p
Validation of a multi-scale simulation strategy based on the Pointwise Strain Superposition Method
No full textThis paper details the experimental validation of a multi-scale simulation strategy that we developed for predicting the stresses and distortions induced by Powder Bed Fusion processes. The strategy comprises a meso-scale model, a macro-scale model, and a scaling method named Pointwise Strain Superposition. The first model evaluates the temperature, stress, and strain fields produced by a single scan line. The scaling method transfers the meso-scale results to the macro-scale model, which is then able to simulate the entire manufacturing process with a reasonable computational cost. The simulation strategy was validated by comparing its results with the stresses and distortions measured on several specimens made of selective laser melted Inconel 718. Stresses were measured through the blind hole drilling method on a cylindrical specimen printed with two different scanning strategies, while distortions were measured on a hollow cylinder and on a cantilever-shaped specimen after removing its supports. In both cases, the simulation showed first- or higher-order accuracy despite the significant uncertainties regarding the input parameters and material properties. This robustness, coupled with its computational efficiency, leads us to believe that our simulation strategy could enhance the process optimization and provide a better understanding of the underlying physical phenomena along with their effects on the manufactured parts
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