Soluzioni per strade in ambiti territoriali protetti

Dopo aver analizzato le principali caratteristiche delle strade extraurbane in alcuni Paesi europei (Italia, Spagna, Francia, Germania), questo articolo compara diverse alternative di manutenzione partendo dalle soluzioni adottate per strade a basso volume di traffico in Italia e in Colombia. Partendo dalle caratteristiche tecniche sono stati analizzati in particolare i costi dei singoli interventi includendo i costi ambientali connessi. Per l'Italia sono stati esaminati due casi di manutenzione stradale: in Toscana ed in Veneto. Per la Colombia si è analizzato il caso della strada di collegamento tra Bogotà ed il parco naturale del Páramo di Sumapaz

Finite Amplitude Wave Propagation in Anisotropic Materials

Often, ultrasound used in nondestructive evaluation is applied to materials that are elastically anisotropic. A few example materials include composites, welds, and rolled metal plates. The influence of elastic anisotropy on the propagation of ultrasound in materials that are linearly elastic is well understood. For example, elastic constants of a composite can be determined reasonably well by measuring phase velocities for propagation in certain directions. However, the influence of elastic anisotropy on nonlinear ultrasonic techniques has received much less attention. In this work, finite amplitude bulk wave propagation is considered for materials with general elastic anisotropy of the second-, third-, and fourth-order elastic constants (anisotropy associated with triclinic symmetry). Three displacement solutions are obtained for arbitrary propagation directions of the three possible bulk wave modes (one quasi-longitudinal and two quasi-transverse). The solution corresponding to each wave mode is a harmonic series having contributions from the fundamental, second-, and third-harmonic waves. The second-harmonic wave amplitude is a function of the quadratic (β) nonlinearity parameter while the thirdharmonic amplitude is a function of both the quadratic and cubic () nonlinearity parameters. β is given in terms of displacement and propagation directions along with elastic tensors that define the second- and third-order elastic constants of the material. An additional contribution from the elastic tensor defining the fourth-order elastic constants is needed to define . Closed-form evaluation of β and for the three different wave modes has been conducted for a variety of materials having different crystallographic point group symmetries. Surfaces will be presented for selected materials, which illustrate the three-dimensional spatial distribution of β and for any propagation direction of the fundamental wave. The vanishing of β for shear waves propagating within material planes of symmetry causes the surface to display the symmetry of the material elegantly. Lastly, straightforward expressions for β and are given for some pure mode directions

Acoustoelasticity of Polycrystalline Materials; a Formalism based on the Self-Consistent Elastic Constants

Elastic constants of polycrystalline materials can be obtained through methods of ensemble averages of the elastic constants belonging to individual grains. Assumptions are often made to relate the local strains (stresses) within individual grains as a result of a macroscopic strain (stress) on the polycrystal. The different assumptions lead to different estimates for the elastic constants of polycrystals. However, an exact formulation is possible, which enforces continuity (at the grain boundaries) between the macroscopic strain (stress) and the strain (stress) in the grain. The resulting estimates of the polycrystal’s elastic constants are known as selfconsistent because either a stress or strain formalism leads to the same estimates. This presentation extends the idea of macroscopic and local continuity of stress and strain and applies it to the theory of acoustoelasticity. Acoustoelasticity describes the dependence of the properties of an elastic wave on the stress state in the material supporting the wave. The selfconsistent formalism enters the elastic constitutive relation developed by C.-S. Man and coworkers. Such a constitutive relation is a function of initial stress, which can be either residual stress resulting from a series of inhomogeneous plastic deformations or generated from external mechanisms. The constitutive relation is used to derive the stress-dependent Christoffel equations for the polycrystal. Solutions to the Christoffel equation yield expressions for the phase velocities and displacement directions of elastic waves in a stressed polycrystal. A comparison is made between phase velocity values based on ensemble averaging originating from the self-consistent formalism and the phase velocities arriving from previous models. The cases in which the present model shows considerable differences from the previous models are presented. This overall goal of this work is to provide a better understanding of the influence of polycrystalline microstructure on acoustoelasticit

Analyzing Structural Changes and Trade Impacts in the Tomato Industry

Almost half of the tomatoes consumed in the U.S. are imported. In 2014, Mexico accounted for more than 80 percent of the tomato imports and Canada for around 10 percent, being the two largest importers of fresh tomato. The accelerated increase of Mexican exports of tomato into the United States has resulted in trade disputes with domestic growers. Under this perspective, the role played by agricultural and economic policy to cope with these matters is studied. Tests for endogenous breakpoints provide information about any policy or economic intervention that could have caused a structural change in the tomato industry from 1970 until 2014. The empirical analysis uses a Vector Autoregressive Model (VAR) model in which the innovation accounting method and Directed Acyclic Graphs (DAGs) are used to show causal flow of information between the variables of interest in contemporaneous time. Results show breakpoints for imports from Canada, imports from Mexico and imports from the rest of the world. This suggests that NAFTA and pricing policies might have caused structural changes especially in the tomato importing industry. DAGs also reveal that these factors have important implications in the tomato industry changing causal relations among variables of interest. Therefore, this study indicates that agricultural policies do affect the underlying causal structure of the U.S. tomato industry

Mode-converted ultrasonic scattering in polycrystals with elongated grains

Elastic wave scattering is used to study polycrystalline media for a wide range of applications. Received signals, which include scattering from the randomly oriented grains comprising the polycrystal, contain information from which useful microstructural parameters may often be inferred. Recently, a mode-converted diffuse ultrasonic scattering model was developed for evaluating the scattered response of a transverse wave from an incident longitudinal wave in a polycrystalline medium containing equiaxed single-phase grains with cubic elastic symmetry. In this article, that theoretical mode-converted scattering model is modified to account for grain elongation within the sample. The model shows the dependence on scattering angle relative to the grain axis orientation. Experimental measurements were performed on a sample of 7475-T7351 aluminum using a pitch-catch transducer configuration. The results show that the mode-converted scattering can be used to determine the dimensions of the elongated grains. The average grain shape determined from the experimental measurements is compared with dimensions extracted from electron backscatter diffraction, an electron imaging technique. The results suggest that mode-converted diffuse ultrasonic scattering has the potential to quantify detailed information about grain microstructure

Mode-converted ultrasonic scattering in polycrystals with elongated grains

Elastic wave scattering is used to study polycrystalline media for a wide range of applications. Received signals, which include scattering from the randomly oriented grains comprising the polycrystal, contain information from which useful microstructural parameters may often be inferred. Recently, a mode-converted diffuse ultrasonic scattering model was developed for evaluating the scattered response of a transverse wave from an incident longitudinal wave in a polycrystalline medium containing equiaxed single-phase grains with cubic elastic symmetry. In this article, that theoretical mode-converted scattering model is modified to account for grain elongation within the sample. The model shows the dependence on scattering angle relative to the grain axis orientation. Experimental measurements were performed on a sample of 7475-T7351 aluminum using a pitch-catch transducer configuration. The results show that the mode-converted scattering can be used to determine the dimensions of the elongated grains. The average grain shape determined from the experimental measurements is compared with dimensions extracted from electron backscatter diffraction, an electron imaging technique. The results suggest that mode-converted diffuse ultrasonic scattering has the potential to quantify detailed information about grain microstructure

An Aeroacoustic Investigation of a Tiltwing eVTOL Concept Aircraft

With the advancement in electric battery design, aircraft designers and manufacturers are no longer constrained to established configurations. Developments in Vertical Take-off and Landing (VTOL) aircraft have also been seen in recent times through the design of modern tiltrotor aircraft such as the AW609 and the V-280 Valor. The combination of these developments allowed engineers to propose designs which utilise the vertical take-off and landing capabilities of a tiltrotor aircraft with electrically driven propulsion systems, deemed eVTOL (Electrically driven Vertical Take-off and Landing). This investigation aims to develop an understanding of the aeroacoustic emissions associated with an eVTOL aircraft, due to acoustics being one of the key components in future certification. The study will consist of an investigation into the baseline design, followed by an optimisation study aiming to reduce the amount of noise generated

Early Science with the Large Millimetre Telescope: Molecules in the Extreme Outflow of a proto-Planetary Nebula

Extremely high velocity emission likely related to jets is known to occur in some proto-Planetary Nebulae. However, the molecular complexity of this kinematic component is largely unknown. We observed the known extreme outflow from the proto-Planetary Nebula IRAS 16342-3814, a prototype water fountain, in the full frequency range from 73 to 111 GHz with the RSR receiver on the Large Millimetre Telescope. We detected the molecules SiO, HCN, SO, and $^{13}$CO. All molecular transitions, with the exception of the latter are detected for the first time in this source, and all present emission with velocities up to a few hundred km s$^{-1}$. IRAS 16342-3814 is therefore the only source of this kind presenting extreme outflow activity simultaneously in all these molecules, with SO and SiO emission showing the highest velocities found of these species in proto-Planetary Nebulae. To be confirmed is a tentative weak SO component with a FWHM $\sim$ 700 km s$^{-1}$. The extreme outflow gas consists of dense gas (n$_{\rm H_2} >$ 10$^{4.8}$--10$^{5.7}$ cm$^{-3}$), with a mass larger than $\sim$ 0.02--0.15 M$_{\odot}$. The relatively high abundances of SiO and SO may be an indication of an oxygen-rich extreme high velocity gas.Comment: Accepted for publication in Monthly Notices of the Royal Astronomical Society Letter

Improving the operating efficiency of the more electric aircraft concept through optimised flight procedures

The increasing awareness of the environmental risks and costs due to the growing demand in aviation has prompted both academic and industrial research into short-term and long-term technologies which could help address the challenges. Among these, the more electric aircraft has been identified as a key design concept which would make aircraft more environmentally friendly and cost effective in the long run. Moreover, the notion of free-flight and optimised trajectories has been identified as a key operational concept which would help curb the environmental effects of aircraft as well as reduce overall costs. The research in this paper presents a methodology in which these two concepts can be coupled to study the benefits of more electric aircraft (MEA) flying optimised trajectories. A wide range of issues from aircraft performance, engine performance, airframe systems operation, power off-take penalties, emission modelling, optimisation algorithms and optimisation frameworks has been addressed throughout the study. The case study is based on a popular short haul flight between London Heathrow and Amsterdam Schiphol. The culmination of the study establishes the advantage of the MEA over conventional aircraft and also addresses the enhanced approach to the classical aircraft trajectory optimisation problem. The study shows that the operation procedures to achieve a minimum fuel burn are significantly different for a conventional aircraft and MEA. Trajectory optimisation reduced the fuel burn by 17.4% for the conventional aircraft and 12.2% for the more electric compared to the respective baseline cases. Within the constraints of the study, the minimum fuel burn trajectory for the MEA consumed 9.9% less fuel than the minimum fuel burn trajectory for the conventional aircraft

Generalized ultrasonic scattering model for arbitrary transducer configurations

Ultrasonic scattering in polycrystalline media is directly tied to microstructural features. As a result, modeling efforts of scattering from microstructure have been abundant. The inclusion of beam modeling for the ultrasonic transducers greatly simplified the ability to perform quantitative, fully calibrated experiments. In this article, a theoretical scattering model is generalized to allow for arbitrary source and receiver configurations, while accounting for beam behavior through the total propagation path. This extension elucidates the importance and potential of out-of-plane scattering modes in the context of microstructure characterization. The scattering coefficient is explicitly written for the case of statistical isotropy and ellipsoidal grain elongation, with a direct path toward expansion for increased microstructural complexity. Materials with crystallites of any symmetry can be studied with the present model; the numerical results focus on aluminum, titanium, and iron. The amplitude of the scattering response is seen to vary across materials, and to have varying sensitivity to grain elongation and orientation depending on the transducer configuration selected. The model provides a pathway to experimental characterization of microstructure with optimized sensitivity to parameters of interest