Ultrasonic distance sensor improvement using a two-level neural network

This paper discusses the performance improvement that a neural network can provide to a contactless distance sensor based on the measurement of the time of flight (TOF) of an ultrasonic (US) pulse. The sensor, which embeds a correction system for the temperature effect, achieves a distance uncertainty (rms) of less than 0.5 mm over 0.5 m by using a two-level neural network to process the US echo and determine the TOF in the presence of environmental acoustic noise. The network embeds a "guard" neuron that guards against gross measurement errors, which would be possible in the presence of high environmental noise

Galaxy formation with radiative and chemical feedback

Here we introduce GAMESH, a novel pipeline which implements self-consistent radiative and chemical feedback in a computational model of galaxy formation. By combining the cosmological chemical-evolution model GAMETE with the radiative transfer code CRASH, GAMESH can post process realistic outputs of a N-body simulation describing the redshift evolution of the forming galaxy. After introducing the GAMESH implementation and its features, we apply the code to a low-resolution N-body simulation of the Milky Way formation and we investigate the combined effects of self-consistent radiative and chemical feedback. Many physical properties, which can be directly compared with observations in the Galaxy and its surrounding satellites, are predicted by the code along the merger-tree assembly. The resulting redshift evolution of the Local Group star formation rates, reionisation and metal enrichment along with the predicted Metallicity Distribution Function of halo stars are critically compared with observations. We discuss the merits and limitations of the first release of GAMESH, also opening new directions to a full implementation of feedback processes in galaxy formation models by combining semi-analytic and numerical methods.Comment: This version has coloured figures not present in the printed version. Submitted to MNRAS, minor revision

STOCHASTIC DYNAMICS OF LARGE-SCALE INFLATION IN DE~SITTER SPACE

In this paper we derive exact quantum Langevin equations for stochastic dynamics of large-scale inflation in de~Sitter space. These quantum Langevin equations are the equivalent of the Wigner equation and are described by a system of stochastic differential equations. We present a formula for the calculation of the expectation value of a quantum operator whose Weyl symbol is a function of the large-scale inflation scalar field and its time derivative. The unique solution is obtained for the Cauchy problem for the Wigner equation for large-scale inflation. The stationary solution for the Wigner equation is found for an arbitrary potential. It is shown that the large-scale inflation scalar field in de Sitter space behaves as a quantum one-dimensional dissipative system, which supports the earlier results. But the analogy with a one-dimensional model of the quantum linearly damped anharmonic oscillator is not complete: the difference arises from the new time dependent commutation relation for the large-scale field and its time derivative. It is found that, for the large-scale inflation scalar field the large time asymptotics is equal to the `classical limit'. For the large time limit the quantum Langevin equations are just the classical stochastic Langevin equations (only the stationary state is defined by the quantum field theory).Comment: 21 pages RevTex preprint styl

A new version of the European tsunami catalogue: updating and revision

A new version of the European catalogue of tsunamis is presented here. It differs from the latest release of the catalogue that was produced in 1998 and is known as GITEC tsunami catalogue in some important aspects. In the first place, it is a database built on the Visual FoxPro 6.0 DBMS that can be used and maintained under the PC operating systems currently available. Conversely, the GITEC catalogue was compatible only with Windows 95 and older PC platforms. In the second place, it is enriched by new facilities and a new type of data, such as a database of pictures that can be accessed easily from the main screen of the catalogue. Thirdly, it has been updated by including the newly published references. Minute and painstaking search for new data has been undertaken to re-evaluate cases that were not included in the GITEC catalogue, though they were mentioned in previous catalogues; the exclusion was motivated by a lack of data. This last work has focused so far on Italian cases of the last two centuries. The result is that at least two events have been found which deserve inclusion in the new catalogue: one occurred in 1809 in the Gulf of La Spezia, and the other occurred in 1940 in the Gulf of Palermo. Two further events are presently under investigation

A revision of the 1783?1784 Calabrian (southern Italy) tsunamis

International audienceSouthern Italy is one of the most tsunamigenic areas in the Mediterranean basin, having experienced during centuries a large number of tsunamis, some of which very destructive. In particular, the most exposed zone here is the Messina Straits separating the coasts of Calabria and Sicily that was the theatre of the strongest Italian events. In 1783?1785 Calabria was shaken by the most violent and persistent seismic crisis occurred in the last 2000 years. Five very strong earthquakes, followed by tsunamis, occurred in a short interval of time (February?March 1783), causing destruction and a lot of victims in a vast region embracing the whole southern Calabria and the Messina area, Sicily. In this study we re-examined these events by taking into account all available historical sources. In particular, we focussed on the 5 and 6 February 1783 tsunamis, that were the most destructive. As regards the 5 February event, we found that it was underestimated and erroneously considered a minor event. On the contrary, the analysis of the sources revealed that in some localities the tsunami effects were quite strong. The 6 February tsunami, the strongest one of the sequence, was due to a huge earthquake-induced rockfall and killed more than 1500 people in the Calabrian village of Scilla. For this event the inundated area and the runup values distribution were estimated. Further, the analysis of the historical sources allowed us to find three new tsunamis that passed previously unnoticed and that occurred during this seismic period. The first one occurred a few hours before the large earthquake of 5 February 1783. The second was generated by a rockfall on 24 March 1783. Finally, the third occurred on 9 January 1784, probably due to a submarine earthquake

Small launch platforms for micro-satellites

The number of small satellites launched into orbit has enormously increased in the last twenty years. The introduction of new standards of micro-satellites has multiplied the launch demand around the world. Nevertheless, not all the missions can easily have access to space: not all kinds of micro-satellites have granted a deployer system and, furthermore, once a micro-satellite is able to reach it, it cannot usually choose its final orbit. Recently two new platforms have been introduced for the release of micro-satellites as piggy-backs. These platforms are totally operative spacecrafts that act like motherships, and allow to select some parameters of the final orbit of the piggy-backs. They provide a solution for three different nano-satellites standard, and at the same time they are being developed in order to reach more powerful orbital release capabilities in the future. The design and the mission of these platforms are described in this paper

Where does galactic dust come from?

Here we investigate the origin of the dust mass (Mdust) observed in the Milky Way (MW) and of dust scaling relations found in a sample of local galaxies from the DGS and KINGFISH surveys. To this aim, we model dust production from Asymptotic Giant Branch (AGB) stars and supernovae (SNe) in simulated galaxies forming along the assembly of aMW-like halo in a well-resolved cosmic volume of 4 cMpc using the GAMESH pipeline. We explore the impact of different sets of metallicity and mass-dependent AGB and SN dust yields on the predicted Mdust. Our results show that models accounting for grain destruction by the SN reverse shock predict a total dust mass in the MW, that is a factor of ~4 less than observed, and cannot reproduce the observed galaxy-scale relations between dust and stellar masses, and dust-togas ratios and metallicity, with a smaller discrepancy in galaxies with low metallicity (12 + log(O/H) < 7.5) and low stellar masses (Mstar < 107 M⊙). In agreement with previous studies, we suggest that competing processes in the interstellar medium must be at play to explain the observed trends. Our result reinforces this conclusion by showing that it holds independently of the adopted AGB and SN dust yields