Synthetic aperture radar images of ocean waves, theories of imaging physics and experimental tests

The physical mechanism for the synthetic Aperture Radar (SAR) imaging of ocean waves is investigated through the use of analytical models. The models are tested by comparison with data sets from the SEASAT mission and airborne SAR's. Dominant ocean wavelengths from SAR estimates are biased towards longer wavelengths. The quasispecular scattering mechanism agrees with experimental data. The Doppler shift for ship wakes is that of the mean sea surface

An Artificial Neural Network based approach for impact detection on composite panel for aerospace application

Fleet maintenance and safety aspects represent a strategic aspect in the managing of the modern aircraft fleets. The demand for efficient techniques of system and structure’s monitoring represent so a key aspect in the design of new generation aircraft. This is even more significant for composite structures that can be highly susceptible to delamination of the ply, which is often very difficult to detect externally and can lead to a dramatic reduction of design strength and service life, as a consequence of impact damage. The purpose of the work is the presentation of an innovative application within the Non Destructive Testing field based upon vibration measurements. The aim of the research has been the development of a Non Destructive Test (NDT) which meets most of the mandatory requirements for effective health monitoring systems while, at the same time, reducing as much as possible the complexity of the data analysis algorithm and the experimental acquisition instrumentation

Numerical Simulation For ANN Training and validation For Impact Detection

Composite structures, today, have a relevant role in our life. The most of the object we use daily are done of composite materials. The recent increase in use of composite materials can be explained if we consider: * They have great strength; * They have low weight; The combination of these two characteristics is the main reason the composite materials are so appreciate in engineering. Every time we need to produce a light structure with high strength composite materials are the good approach to design it. Instead of benefits, composite materials have also some issues. From a structural point of view the most critical is the difficult to monitoring them. Metal materials integrity is easy to check, the most of the time a visual inspection is enough to detect failures also in early stage. In composite materials, due the way they are maiden, often is impossible detect failures until it is too late to repair them. The most common problem composite materials have is the delamination. It consists in a detachment of plys inside the material due to an impact on the material itself. From an exterior point of view it is impossible to detect by eye. It suddenly propagates inside the structure inducing failures. The task of this work is to develop an artificial neural network (ANN) able to detect impacts and restrict the part of structure to monitor looking for damages. I

Acoustic properties of materials: A comparison of numerical and experimental methods

Acoustic simulations provide today a valid tool to simulate complex environments and complex interaction between acoustic and structure. Multiple methods are nowadays available with different degrees of accuracy and different applications. Simulation methods cover a wide frequency range with FE methods dominating the low frequency range. SEA mostly covers high frequency range with BEM covering an intermediate frequency range. Ray-tracing can work on the entire frequency range and is used when a large domain must be simulated. These methods require acoustic properties of materials to be implemented such as acoustic impedance or absorption and STL. The aim of this paper is to show different methods to provide these properties and discuss about the equivalence/difference of the numerical and experimental approaches under specific assumptions

Colour and stellar population gradients in galaxies

We discuss the colour, age and metallicity gradients in a wide sample of local SDSS early- and late-type galaxies. From the fitting of stellar population models we find that metallicity is the main driver of colour gradients and the age in the central regions is a dominant parameter which rules the scatter in both metallicity and age gradients. We find a consistency with independent observations and a set of simulations. From the comparison with simulations and theoretical considerations we are able to depict a general picture of a formation scenario.Comment: 4 pages, 4 figures. Proceedings of 54th Congresso Nazionale della SAIt, Napoli 4-7 May 201

Evolution of central dark matter of early-type galaxies up to z ~ 0.8

We investigate the evolution of dark and luminous matter in the central regions of early-type galaxies (ETGs) up to z ~ 0.8. We use a spectroscopically selected sample of 154 cluster and field galaxies from the EDisCS survey, covering a wide range in redshifts (z ~ 0.4-0.8), stellar masses ($\log M_{\star}/ M_{\odot}$ ~ 10.5-11.5 dex) and velocity dispersions ($\sigma_{\star}$ ~ 100-300 \, km/s). We obtain central dark matter (DM) fractions by determining the dynamical masses from Jeans modelling of galaxy aperture velocity dispersions and the $M_{\star}$ from galaxy colours, and compare the results with local samples. We discuss how the correlations of central DM with galaxy size (i.e. the effective radius, $R_{\rm e}$), $M_{\star}$ and $\sigma_{\star}$ evolve as a function of redshift, finding clear indications that local galaxies are, on average, more DM dominated than their counterparts at larger redshift. This DM fraction evolution with $z$ can be only partially interpreted as a consequence of the size-redshift evolution. We discuss our results within galaxy formation scenarios, and conclude that the growth in size and DM content which we measure within the last 7 Gyr is incompatible with passive evolution, while it is well reproduced in the multiple minor merger scenario. We also discuss the impact of the IMF on our DM inferences and argue that this can be non-universal with the lookback time. In particular, we find the Salpeter IMF can be better accommodated by low redshift systems, while producing stellar masses at high-$z$ which are unphysically larger than the estimated dynamical masses (particularly for lower-$\sigma_{\star}$ systems).Comment: 14 pages, 6 figures, 3 tables, MNRAS in pres

ANALYTICAL AND NUMERICAL MODELS FOR THE AERODYNAMIC NOISE PREDICTION OF AN HIGH-SPEED TRAIN PANTOGRAPH

The present work deals with the aeroacoustic analysis of a three-dimensional pantograph model, through the employment of an innovative analytical approach and a 3D numerical modeling. Specifically, the proposed analytical approach, aimed to predict the noise emission, is based on a modified formulation of the Smith and Chow's formula. Namely, by considering the entire landing gear structure as a sum of cylindrical elements, each cylinder noise has been individually calculated by the formula, as a result, based on the superposition principle, the whole noise is obtained; considering that the pantograph can also be considered as a sum of cylindrical elements, this formula, initially developed for aircraft landing gears, has been optimized and calibrated for the purpose of the present study. Because of, the analytical formula does not take obviously into account several effects related to the noise generation mechanism, a 3D numerical aeroacoustic model of the pantograph was needed. Specifically, the theoretical background adopted is the Williams and Hawkings acoustic analogy, an evolution of the well-known Lighthill acoustic analogy. The latter consists in the substitution of the noise generating surface with a distribution of dipole punctual sound sources, whose intensity is proportional to the temporal variation of fluid dynamic quantities acting in that point. As a result, a more detailed characterization of the noise spectrum can be provided. The analytical and numerical results have been then compared in terms of sound pressure levels and a well spectral contents, to themselves and to available experimental data

The income gap reporting framework in public not-for-profit organizations: the British Museum case

The income gap is the negative margin between earned income and operating expenses: this is the main financial concern for not-for-profit entities (both public sector and nongovernmental organizations). Despite this, all over the world these entities are forced to use the standard profit-centered income statements format, with its focus on net income generation (the bottom line). This paper proposes an income statement format that uses the income gap to understand/discuss/present the financial viability of a not-for-profit entity in the arts sector, specifically a museum. We apply the framework to the British Museum's income statements from 1999-2000 to 2018-2019. This allows us to analyze institutional narratives in the context of the evolution of the museum's financial viability over two decades, and to assess the performance of the museum's neoliberal reform agenda from the end of the 1990s. Enlarging the perspective, ad hoc adaptations of the framework can allow a better understanding of the financial viability of not-for-profit organizations, in the arts sector and possibly more broadly in public services and not-for-profit sector