1,155 research outputs found
On the Choice of Tool Material in Friction Stir Welding of Titanium Alloys
No full textFriction Stir Welding (FSW) is a solid state welding process patented in 1991 by TWI; initially adopted to weld aluminum alloys, is now being successfully used also for magnesium alloys, copper and steels. The wide diffusion the process is having is due to the possibility to weld both materials traditionally considered difficult to be welded or "unweldable" by traditional fusion welding processes due to peculiar thermal and chemical material properties, and complex geometries as sandwich structures and straightening panels. Recently, research is focusing on titanium alloys thanks to the high interest that such materials are getting from the industry due to the extremely high strength-weight ratio together with good corrosion resistance properties. At the moment, the main limit to the industrial applicability of FSW to titanium alloys is the tool life, as ultra wear and deformation resistant materials must be used. In this paper a, experimental study of the tool life in FSW of titanium alloys sheets at the varying of the main process parameters is performed. Numerical simulation provided important information for the fixture design and analysis of results. Tungsten and Rhenium alloy W25Re tools are found to be the most reliable among the ones considered
Actions for plant biodiversity improvement and recovery in lowland ancient woods and artificial forest stands
No full textItalian forest ecosystems, characterized by a long tradition of forestry and agro-pastoral practices that have guided their evolution, have ensured the preservation over time of significant aspects of naturalness to which important landscape,ecological (carbon stock) and recreational values are associated.
These functions have become increasingly important leading to the implementation of several reforestation projects. Nevertheless, the new forest stands, born on lands subject to agricultural use for a long time, evolve into ecologically sustainable ecosystems only in a very long time.
One of the main findings of this process is represented both by the structure of biological communities and their complexity, which remain greatly simplified for a long time.
In particular, nemoral herbaceous species, which represent the most valuable and ecologically significant component of a forest habitat, remain confined to the ―ancient forests‖. These species, closely habitat-specific and substantially unable to adapt to the environmental changes (Buffa and Villani in pubbl.; Eckert, 2002; Honnay et al., 1999), are in risk of local extinction due to the small size and isolation of their populations.
In order to preserve the venetian lowland ecotypes, some experiments were started in 2010 with the aim of producing some target species (Arum maculatum L., Allium ursinum L., Asparagus tenuifolius Lam., Carex remota L., Colchicum autumnale L., Mercurialis perennis L., Lamium orvala L., Leucojum vernum L., Loncomelos pyrenaicum (L.) Hrouda ex J. Holub s.l., Paris quadrifolia L., Ranunculus auricomus L., Viola reichenbachiana Jordan ex Boureau).
The peculiarities of the environment in which these species are adapted impose a continuous integration of autoecology knowledge with plant nursery techniques. Thus in situ (ancient forest) and ex situ (germination room and outdoors cultivation tunnel) germination tests were carried out to understand how soil variables (texture, pH, organic C, N, P), physical environment variables (quantity and quality of light radiation in the undergrowth) and microclimatic variables (soil T at 0 cm) allow to break dormancy, induce germination and promote seedlings recruitment.
The comparison of in situ and ex situ tests showed that for the majority of the species germinating output is significantly higher in natural conditions or artificial conditions that simulate more accurately the natural ones than in germination room.
Seeds of some species kept at 20 ° C in dry storage (eg. Leucojum vernum L., Mercurialis perennis L.) showed a reduction of viability even more than 80% in 6 months since the collection date, proving potential recalcitrance, and explaining the negative results for their germination tests.
The first results encourage further tests in order to implement the knowledge on the production of these species, which is desirable both in terms of biodiversity conservation, and for the reinforcement of existing populations or for the naturalization of artificial forests. A new frontier, finally, may be offered by their use in private gardens (for aesthetic and naturalistic reasons, in a sort of transposition of the bird-gardening practice within the conservation of nemoral species), with the activation of a production chain giving also employment benefits
Aspetti fitogeografici e fitosociologici della vegetazione a Quercus ilex L. di Arco (TN).
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Numerical investigation on dissimilar Friction Stir Welding of Aluminum and Magnesium sheets
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The many faces of mathematical modelling in oncology
No full textThe application of modelling to solve problems in biology and medicine, and specifically in oncology and radiation therapy, is increasingly established and holds big promise. We provide an overview of the basic concepts of the field and its current state, along with new tools available and future directions for research. We will outline radiobiology models, examples of other anticancer therapy models, multiscale modelling, and we will discuss mechanistic and phenomenological approaches to modelling
A SIMULATION TOOL ASSISTING THE DESIGN OF A CLOSE RANGE PHOTOGRAMMETRY SYSTEM FOR THE SARDINIA RADIO TELESCOPE
No full textThe Sardinia Radio Telescope (SRT) is a 64 m diameter antenna, whose primary mirror is equipped with an active surface capable
to correct its deformations by means of a thick network of actuators. Close range photogrammetry (CRP) was used to measure the
self-load deformations of the SRT primary reflector from its optimal shape, which are requested to be minimized for the radio telescope
to operate at full efficiency. In the attempt to achieve such performance, we conceived a near real-time CRP system which requires the
cameras to be installed in fixed positions and at the same time to avoid any interference with the antenna operativeness. The design
of such system is not a trivial task, and to assist our decision we therefore developed a simulation pipeline to realistically reproduce
and evaluate photogrammetric surveys of large structures. The described simulation environment consists of (i) a detailed description
of the SRT model, included the measurement points and the camera parameters, (ii) a tool capable of generating realistic images
accordingly to the above model, and (iii) a self-calibrating bundle adjustment to evaluate the performance in terms of RMSE of the
camera configurations
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