122,070 research outputs found
Foreword. In Dalla Vecchia W., Cassiopeia per quattro chitarre (1989), a cura di N. Mazzon, Padova: Armelin Musica 2014, pp. I-VII.
No full textApplication of a hybrid approach to the design of anchored wire meshes on steep slopes
No full textAnchored steel meshes are commonly employed stabilising systems for potentially unstable granular layers (e.g. soil or highly fragmented weak rock) on slopes against translational failure mechanisms. They are usually conceived as passive stabilising intervention (i.e. their stabilising action is provided only upon the activation of a given displacement field into the unstable layer). As a consequence, standard design methods, generally based on ultimate limit state (ULS) approaches, can potentially be largely unsafe, since they assume the full mobilisation of both the ultimate soil resistance and the ultimate tensile force in the steel mesh independently
of the displacement amplitude of the unstable layer. In this paper a design procedure, based on so called ‘hybrid’ approaches, is described with specific reference to relatively steep slopes. The key concept is the use of a suitable characteristic curve, describing the mechanical response of the entire system (steel plate, steel mesh, soil layer) as a function of the displacement amplitude, thus providing a safe and consistent estimation of the mobilised stabilising action for the required safety level
Correlation of bois noir disease with nettle and vector abundance in northern Italy vineyards
No full textThe phytoplasmas associated with bois noir (BN) tuf-type a are transmitted to grapevines by means of Hyalesthes obsoletus Signoret using Urtica dioica L. as the inoculum source. In the period 2003–2008, a research was carried out in six vineyards of northern Italy where a large amount of nettles in the ditches surrounding vineyards was detected. The aim was to establish the nettle control effects on the presence of H. obsoletus and new symptomatic grapevines. PCR and RFLP analyses showed the presence of the BN tuf-type a phytoplasmas in symptomatic grapevines of all vineyards and in the vector. Weed control strategies along ditches were always associated with decreases in nettle coverage and H. obsoletus numbers. A reduction in the percentage of new symptomatic grapevines occurred in all vineyards except for one vineyard where the least reduction in nettle and H. obsoletus was observed. The decrease in H. obsoletus population was significantly correlated with a decrease in nettles along ditches, and the reduction in H. obsoletus population was correlated with a decrease in incidence of new symptomatic grapevines compared with the incidence before the application of weed control measures. Nettle weeding can reduce the incidence of BN tuf-type a, but weed control costs and impacts need to be considered
Introduzione in Abruzzo di Neodryinus typhlocybae (Ashmead) per la lotta biologica contro Metcalfa pruinosa (Say).
No full textParticle-based modelling of cortical meshes for soil retaining applications
No full textMetallic cortical wire meshes are extensively used to protect slopes and infrastructures in mountain regions. These structures are constituted by periodic patterns of steel wires and have a ductile non-linear behaviour. The installed mesh panels generally experience non-trivial boundary conditions which combined with their high deformability and the chance of local ruptures make these structures difficult to be modelled as a contin-uum. The Discrete Element Method (DEM) is particularly well suited for modelling the soil-mesh interaction problem, taking advantage of its potentials in handling large deformation, contact-detachment and interlock-ing between particles and the mesh. The mesh is modelled with two approaches and a puncture test on a single mesh panel is used for calibration. After that a simplified soil-mesh problem with a single mesh panel is con-sidered and compared with the results of a punch-mesh problem. The force-displacement behaviour experi-enced by anchors and edges of the panels are also discussed
Enhancement of Design Methodologies of Anchored Mesh Systems Using the Discrete Element Method
No full textThe understanding of the mechanical behavior of anchored mesh
systems for slope stabilization represents a challenging task for engineers.
Standard laboratory tests are in general not representative of the in-situ conditions.
Moreover, the complex interaction between the mesh and the retained
material is not trivial to reproduce numerically. In this study a simplified in-situ
condition is analyzed using the discrete element method (DEM). Starting from
the tensile stress-strain relationships acting on each wire it is possible to
determine the force sustained by the mesh system and to derive the displacement
field of the mesh panel. Therefore, the progressive activation of the mesh
retaining capacity, during the loading of these structures can be obtained providing
the evolution of the mechanical response of the system. The information
obtained with the discrete element simulation highlights the possible improvements
of the classical design methodologies and shows the potential of the
presented approach for the comprehension of the mechanical behavior of
anchored mesh systems
Effect of stress on the paracellular barrier in the rat ileum
No full textBackground: Restraint stress induces permeability changes in the rat small intestine but little is known of the ultrastructural events leading to defects of the paracellular sealing or of the short term evolution of these alterations.
Methods: In the present study, we performed transmission electron microscopy in the terminal ileum perfused with lanthanum after two hours of immobilisation stress and in non-stressed control rats. Moreover, immunohistochemistry of the tight junction (TJ) associated proteins, occludin and zonula occludens 1 (ZO-1), was carried out together with western blot analysis of the transmembrane protein occludin. TJ morphology was also assessed after a 22 hour recovery period.
Results: Immobilisation stress induced a significant increase in epithelial permeability to the lanthanum tracer (p<0.005) which recovered completely after 22 hours. Compared with unstressed controls, in stressed rats no differences were found on freeze fracture analysis. The TJ related immunofluorescence signals of occludin and of ZO-1 were irregularly distributed in stressed rats after two hours but returned to a normal pattern at 24 hours although with minor intensity. No quantitative alterations in occludin were detectable in stressed rats by immunoblot whereas a perinuclear concentration of occludin was observed by immunolocalisation.
Conclusions: Immobilisation stress induced an increase in TJ permeability in the rat terminal ileum. These changes were mainly due to modifications and redistribution of the TJ transmembrane protein occludin and of the plaque protein ZO-1 whereas protein synthesis, at least that of occludin, was not affected by stress
Discrete element modelling of a soil-mesh interaction problem
No full textThe design strategies of metallic cortical meshes used for slope protection are mostly linked to the application of empirical and semi-empirical methods. This limitation is due to the difficulties in representing such complex large-deformation rock-soil-structure interaction problems: the intrinsic complexities of these structures is combined with the difficulties in describing the geometry both the mechanical and physical properties of the rock and soil behind. The Discrete Element Method proved their effectiveness in describing the non-linear and large strain behaviour of the soil, and recently also the mechanical response of steel wire meshes which are represented as regular patterns of remote interactions between nodes. In this work, a discrete element model of a double-twisted hexagonal wire mesh is calibrated on the base of experimental tensile tests on two wire types. The validation of the model is performed using the results of a standard punch test. The same mesh is then loaded by a granular layer constituted by discrete element particles mimicking the soil earth pressure. A comparison between the two load types is discussed with reference to the force-displacement curve and the distribution of the tensile stresses on the mesh panel. The effect of the boundary conditions is also analysed
Changes in soil phenol oxidase activities due to long-term application of compost and mineral N in a walnut orchard
No full textPhenol oxidases (POs) are a group of soil extracellular oxidoreductase enzymes, which are involved in oxidative processes related to nutrient cycling. This class of enzymes has multiple functions at both the organism and ecosystem level and can trigger either positive or negative feedback loops between soil organisms and soil organic matter.
The purpose of this study was to evaluate: (i) whether PO activities have a trend different from those of microbial biomass and activity; and (ii) whether PO activities are enhanced or reduced by fertilizer application.
Soil samples were taken from plots in a 14-year-old experimental walnut orchard, subjected, since planting, to three fertilizer treatments: organic (compost) or mineral (urea) fertilization at the same rate of nitrogen application (100 kg N ha− 1), or left unfertilized. Soil samples were divided according to sampling depth (0–20 cm and 20–40 cm).
Results showed that the application of compost significantly increased C and N pools. qCO2 and DHD/Cext data indicated that the biota at 20–40 cm soil depth was more stressed or mainly composed of microorganisms with low substrate utilization efficiency. Phenol oxidase, tyrosinase, and catechol oxidase activities were significantly promoted in the surface layer by compost addition. In contrast, laccase activity showed a large increase in the deeper soil layer when supplied with mineral N, whereas compost addition led to increased activity in the surface layer. These findings suggest that soil phenol oxidases play a part in the determination of soil functionality, but they need to be investigated in greater depth in order to understand the mechanisms regulating their activities
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