Experimental tests on shallow foundations of onshore wind turbine towers

The current effort towards the progressive switch from carbon-based to renewable energy production is leading to a relevant spreading of both on- and off-shore wind turbine towers. Regarding reinforced concrete shallow foundations of onshore wind turbine steel towers, possible reductions of reinforcement may increase their sustainability, speed of erection, and competitiveness. The article presents the results of an experimental program carried out at Politecnico di Milano concerning both cyclic and monotonic loading, simulating extreme wind conditions on 1:15 scaled models of wind turbine steel towers connected by stud bolt adapters to reinforced concrete shallow foundations embedded in a sandy soil. Three couples of foundation specimens were tested with different reinforcement layouts: (a) similar to current praxis, (b) without shear reinforcement, and (c) without shear reinforcement and with 50% of ordinary steel rebars replaced by steel fibers. Additional vertical loads were added to the small-scale models in order to ensure similarity in terms of stresses. The test results allowed to (i) characterize the mechanical behavior of the foundation element considering soil-structure interaction under both service and ultimate load conditions, (ii) assess the foundation failure mode, (iii) highlight the role of each typology of reinforcing bars forming the cage, and (iv) provide hints for the optimization of these latter

Why does gravitational radiation produce vorticity?

We calculate the vorticity of world--lines of observers at rest in a Bondi--Sachs frame, produced by gravitational radiation, in a general Sachs metric. We claim that such an effect is related to the super--Poynting vector, in a similar way as the existence of the electromagnetic Poynting vector is related to the vorticity in stationary electrovacum spacetimes.Comment: 9 pages; to appear in Classical and Quantum Gravit

The technical causes of the collapse of Annone overpass on SS.36

The paper presents the technical causes of the collapse of Annone overpass, which occurred in October 2016. The tests carried out to identify the characteristics of the materials used for the construction, the verification calculations that led to the identification of the critical mechanism in the collapse and the test on the structural element deemed critical at the time of collapse are summarized. The paper highlights the critical issues occurring concurrently with the passage of the exceptional transports, the safety coefficient in relation to the project loads at the time of construction and that at the time of the passage of the exceptional convoy. The note also highlights some critical aspects of the national infrastructural system, with particular reference to exceptional transports and the methods that could be used to prevent future accidents in the absence of macro-design mistake

On the stability of the shear-free condition

The evolution equation for the shear is reobtained for a spherically symmetric anisotropic, viscous dissipative fluid distribution, which allows us to investigate conditions for the stability of the shear-free condition. The specific case of geodesic fluids is considered in detail, showing that the shear-free condition, in this particular case, may be unstable, the departure from the shear-free condition being controlled by the expansion scalar and a single scalar function defined in terms of the anisotropy of the pressure, the shear viscosity and the Weyl tensor or, alternatively, in terms of the anisotropy of the pressure, the dissipative variables and the energy density inhomogeneity.Comment: 19 pages Latex. To appear in Gen. Rel. Gra

Review on imidacloprid diffusion route and a case study: from apple orchard to the honey bee colony matrices

Honey bees play a pivotal role in natural and rural ecosystems by providing human and animal food sources through pollination services. However, in cultivated areas, they can be exposed to the chemicals utilized for crop protection. Neonicotinoid insecticides can adversely affect honey bee colonies impairing their survival, immunity and biological activities at lethal and sublethal doses. For this reason, neonicotinoids, together with other stress factors, like pathogens (e.g. viruses and Varroa mites), climate change and food shortage, are considered one of the causes of worldwide colony losses. Nevertheless, the natural way of entry and diffusion of these pesticides in field colonies is not completely clear. Here, we wanted to fill this gap by studying the diffusion route of imidacloprid and its metabolites by analysing different matrices collected from honey bee colonies used for pollination of apple orchards, in the framework of applied Integrated Pest Management strategies. Pollen, honey bees, honey, royal jelly, bee wax and bee bread were sampled from 6 honey bee colonies placed in two different apple orchards before blooming, exposed to chemicals application and removed from the site after that. Samples were analysed using a liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) and gas chromatography-tandem mass spectrometry (GC-MS/MS) in order to detect imidacloprid, olefin imidacloprid and 5-hydroxy imidacloprid. The results demonstrate that the primary way of entrance of imidacloprid was the pollen transported by foragers, while the main accumulation matrices were bee bread, honey and wax. These findings allow us to hypothesize that the accumulation of this insecticide, especially in bee bread, the main larval food, could potentially impact negatively on honey bee wellbeing at the adult stage. Moreover, our data could implement the honey bee colony simulato

Thermodynamics and Kinetic Theory of Relativistic Gases in 2-D Cosmological Models

A kinetic theory of relativistic gases in a two-dimensional space is developed in order to obtain the equilibrium distribution function and the expressions for the fields of energy per particle, pressure, entropy per particle and heat capacities in equilibrium. Furthermore, by using the method of Chapman and Enskog for a kinetic model of the Boltzmann equation the non-equilibrium energy-momentum tensor and the entropy production rate are determined for a universe described by a two-dimensional Robertson-Walker metric. The solutions of the gravitational field equations that consider the non-equilibrium energy-momentum tensor - associated with the coefficient of bulk viscosity - show that opposed to the four-dimensional case, the cosmic scale factor attains a maximum value at a finite time decreasing to a "big crunch" and that there exists a solution of the gravitational field equations corresponding to a "false vacuum". The evolution of the fields of pressure, energy density and entropy production rate with the time is also discussed.Comment: 23 pages, accepted in PR

Irreversible Processes in Inflationary Cosmological Models

By using the thermodynamic theory of irreversible processes and Einstein general relativity, a cosmological model is proposed where the early universe is considered as a mixture of a scalar field with a matter field. The scalar field refers to the inflaton while the matter field to the classical particles. The irreversibility is related to a particle production process at the expense of the gravitational energy and of the inflaton energy. The particle production process is represented by a non-equilibrium pressure in the energy-momentum tensor. The non-equilibrium pressure is proportional to the Hubble parameter and its proportionality factor is identified with the coefficient of bulk viscosity. The dynamic equations of the inflaton and the Einstein field equations determine the time evolution of the cosmic scale factor, the Hubble parameter, the acceleration and of the energy densities of the inflaton and matter. Among other results it is shown that in some regimes the acceleration is positive which simulates an inflation. Moreover, the acceleration decreases and tends to zero in the instant of time where the energy density of matter attains its maximum value.Comment: 13 pages, 2 figures, to appear in PR

Antarctic Climate Change and the Environment

The Antarctic climate system varies on timescales from orbital, through millennial to sub-annual, and is closely coupled to other parts of the global climate system. We review these variations from the perspective of the geological and glaciological records and the recent historical period from which we have instrumental data (the last 50 years). We consider their consequences for the biosphere, and show how the latest numerical models project changes into the future, taking into account human actions in the form of the release of greenhouse gases and chlorofluorocarbons into the atmosphere. In doing so, we provide an essential Southern Hemisphere companion to the Arctic Climate Impact Assessment