Small bodies centroiding via image processing and convolutional neural network

LAUREA MAGISTRALECome l’interesse della comunità scientifica per gli small bodies cresce, così il design delle sonde cerca di adattarsi al particolare ambiente che questi impongono. L’uso di immagini per navigare attorno a questi corpi è diventato quasi uno standard negli ultimi anni, ma la richiesta di maggiore precisione, robustezza e autonomia spinge la ricerca verso nuovi approcci. Il campo del machine learning e del deep learning ha offerto molti strumenti per migliorare l’attuale tecnologia, tanto che con loro è possibile sostituire del tutto o in parte la GNC. In questo lavoro è indagata la possibilità di utilizzare una rete neurale convoluzionale per risolvere il problema del centroiding. Il risultato è poi confrontato con altre due tecniche, provenienti dall’image processing, che sono analizzate. Inizialmente, la rete è sottoposta a un training, sfruttando la tecnica del transfer learning, con un set fatto di 21000 immagini sintetiche ottenute con Blender dai modelli di 6 corpi. In seguito, è affrontato il problema della specializzazione del network su alcuni nuovi corpi, indagando anche l’effetto della mancanza di immagini per il training. Il CNN ha mostrato una performance migliore delle altre tecniche sviluppate, con tutti i corpi considerati.As small bodies interest by the scientific community continues to grow, spacecraft design tries to adapt itself to the particular environment these targets dictate. The use of optical images to navigate around these bodies has become nearly a standard in the last years, but the request of precision, robustness and autonomy push the research toward different and more innovative approaches. The field of machine learning and deep learning has offered many tools to improve the existing technology, such that it can substitute completely the GNC loop or some of its parts. In this work the possibility to use a convolutional neural network (CNN) for solving the problem of centroid is investigated. The resulting output is compared with other two traditional image processing techniques, which are analysed in the work. Initially, the CNN is trained, taking advantage of transfer learning, on a set of 21000 synthetic images obtained with Blender, composed of 6 small body shape models. Then is faced the problem of specialising the network to some new shapes, investigating also the effect of lack of data to the training. The CNN has shown to be better than the other techniques developed, with all the bodies considered

La città di Porto : granito su granito. Centro culturale al Passeio Fontainhas

LAUREA MAGISTRALEPasseio Fontainhas. La roccia conquistata e custodita Il progetto si colloca tra Passeio Fontainhas e Avenida Eiffel in una zona di Porto subito al di fuori della traccia ancora visibile della Muralha Fernandina, verso est. L’area si presenta come una striscia di terreno - sviluppata longitudinalmente rispetto alla sponda settentrionale del Douro - che scende a precipizio verso il fiume. Qui si riconoscono radi terrazzamenti che, con andamento sconnesso e disordinato, si addossano agli edifici. Questo vuoto a strapiombo sul fiume è segnato dalla natura rocciosa che caratterizza l’intera città. Quest’area, come si legge nella cartografia storica, è sempre rimasta isolata rispetto allo sviluppo urbano, ponendosi come zona periferica separata dal contesto e senza alcuna connessione con la parte della città che le si addossa a nord. Questo problema, legato alla sua specifica conformazione geomorfologica, è stato ulteriormente rimarcato dalla costruzione del viadotto Duque de Loulé, che crea in questa zona un taglio netto con la parte di città rivolta verso il fiume e che impedisce definitivamente qualsiasi collegamento diretto di questo luogo con la struttura urbana circostante. Obiettivo del progetto è quello di conferire ordine attraverso un nuovo disegno capace di definire il ruolo di questa massa di granito, che non ha mai avuto una configurazione precisa. Il carattere impervio della costa sembra impedire il collegamento tra i due sistemi: la città e il fiume. Attraverso il progetto, l’ostacolo diventa occasione di risignificazione del rapporto tra natura e architettura. Prendendo come paradigma interpretativo l’architettura tipica del paesaggio del Douro e della stessa città di Porto, cioè la costruzione del paesaggio attraverso i terrazzamenti, il progetto si impadronisce del terreno, dove ce ne sia la possibilità. L’architettura dunque conquista, ma allo stesso tempo difende la natura di pietra. È così che si costruiscono tre possenti e massicci muri laddove la montagna ne ha bisogno e, allo stesso tempo, lo consente. Dal terrazzamento viene creato un edificio che sostiene la terra ma che parallelamente ne prende possesso al suo interno. Muri interamente di granito, che rafforzano l’immagine della parete naturale e che sono rappresentativi di un sostegno per la città e al contempo della possibilità dell’uomo di imprimere valore estetico all’ordine naturale, con lo scopo di creare lo spazio necessario allo svolgersi della vita. Un progetto ipogeo che prende possesso di ciò che è suo e di ciò che può indagare, rispettando la forza della montagna e dialogando con essa, attraverso un fitto sistema di relazioni che rendono chiare le possibilità costruttive insite nel luogo. Solo in pochi e misurati punti il progetto si apre: si mostra all’esterno attraverso la sua sezione, tramite episodi che, come figure autonome rispetto al resto della composizione, rivelano un ordine e una misura che descrive questa città sotterranea, disegnata all’interno della pietra

SfM-based method to assess gorgonian forests (Paramuricea clavata (Cnidaria, Octocorallia))

Animal forests promote marine habitats morphological complexity and functioning. The red gorgonian, Paramuricea clavata, is a key structuring species of the Mediterranean coralligenous habitat and an indicator species of climate effects on habitat functioning. P. clavata metrics such as population structure, morphology and biomass inform on the overall health of coralligenous habitats, but the estimation of these metrics is time and cost consuming, and often requires destructive sampling. As a consequence, the implementation of long-term and wide-area monitoring programmes is limited. This study proposes a novel and transferable Structure from Motion (SfM) based method for the estimation of gorgonian population structure (i.e., maximal height, density, abundance), morphometries (i.e., maximal width, fan surface) and biomass (i.e., coenenchymal Dry Weight, Ash Free Dried Weight). The method includes the estimation of a novel metric (3D canopy surface) describing the gorgonian forest as a mosaic of planes generated by fitting multiple 5 cm × 5 cm facets to a SfM generated point cloud. The performance of the method is assessed for two different cameras (GoPro Hero4 and Sony NEX7). Results showed that for highly dense populations (17 colonies/m2), the SfM-method had lower accuracies in estimating the gorgonians density for both cameras (60% to 89%) than for medium to low density populations (14 and 7 colonies/m2) (71% to 100%). Results for the validation of the method showed that the correlation between ground truth and SfM estimates for maximal height, maximal width and fan surface were between R2 = 0.63 and R2 = 0.9, and R2 = 0.99 for coenenchymal surface estimation. The methodological approach was used to estimate the biomass of the gorgonian population within the study area and across the coralligenous habitat between −25 to −40 m depth in the Portofino Marine Protected Area. For that purpose, the coenenchymal surface of sampled colonies was obtained and used for the calculations. Results showed biomass values of dry weight and ash free dry weight of 220 g and 32 g for the studied area and to 365 kg and 55 Kg for the coralligenous habitat in the Marine Protected Area. This study highlighted the feasibility of the methodology for the quantification of P. clavata metrics as well as the potential of the SfM-method to improve current predictions of the status of the coralligenous habitat in the Mediterranean sea and overall management of threatened ecosystems

Generic Decoding of Restricted Errors

Several recently proposed code-based cryptosystems base their security on a slightly generalized version of the classical (syndrome) decoding problem. Namely, in the so-called restricted (syndrome) decoding problem, the error values stem from a restricted set. In this paper, we propose new generic decoders, that are inspired by subset sum solvers and tailored to the new setting. The introduced algorithms take the restricted structure of the error set into account in order to utilize the representation technique efficiently. This leads to a considerable decrease in the security levels of recently published code-based cryptosystems

Strong enhancement of graphene plasmonic emission by quantum Čerenkov effect in confined structures

One notable issue in low terahertz (THz) applications is to achieve sources with higher output power than the state of the art. One possible solution to the foregoing problem is to amplify the electromagnetic field emitted by already accessible THz generators. Here, we study the quantum Cerenkov effect as a possible explanation for low-THz amplification, which has been found experimentally elsewhere. Specifically, the emission of surface plasmons from traveling electrons in mono-dimensional graphene, mediated by charge–field interaction, is shown to provide in-plane electromagnetic radiation down to THz and mm-wave frequencies. We focus on a structure consisting of a graphene layer between metal electrodes, which enhance the field confinement and lead to a linearization of the plasmon dispersion in the frequency domain. When compared to a non-confined plasmonic radiation, the above-mentioned configuration shows emission rates ten times larger, which make it promising for THz amplification

Band gap and THz optical adsorption of SnSe and SnSe2 nanosheets on graphene: Negative dielectric constant of SnSe

Density functional theory (DFT) calculations have been used to investigate physical–chemical sensing of various proposed interfaces as SnSe@Graphene, SnSe2@Graphene, Graphene@SnSe@Graphene, and Graphene@SnSe2@Graphene, where dispersion corrections have been included to taken into account the vdW interactions between the layers. Initially, we predicted the electronic structures, mobility and carrier concentrations (cc) of SnSe and SnSe2 structures. Using different methodology, the outcomes have confirmed the semiconductor properties of SnSe and SnSe2 with indirect bandgap of 1.20 eV and 0.94 eV calculated by Generalized Gradient Approximation (GGA) and MetaGGA (MGGA) adopted with Perdew-Burke-Ernzerhof (PBE) functional, while hybrid Heyd-Scuseria-Ernzerhof (HSE) hybrid functional overestimated the experimental observations for both materials. Room temperature high mobility and cc have predicted by 126 × 103 cm2V−1 s−1 with cc of 1.3 × 1013 cm3 for a two layers SnSe and 69 × 103 cm2V−1 s−1 with cc of 4.2 × 1018 cm3 for three layers SnSe2. Optical absorption spectrum revealed that the presence of two peaks at 60 THz and 48 THz with the intensity of 89879 cm−1 and 34504 cm−1 for interfaces including two layers of graphene. More interestingly, dielectric constant calculations showed that the transfer of carriers between graphene layers and SnSe in Graphene@SnSe@Graphene interface with absorption peak shifted to 24 THz along the in-plane direction and negative dielectric constants in the range of 24–169 THz, showing the effect of light-trapping through plasmonic

Strengths and Weaknesses of the Analytical Techniques Used for Measuring Low Mercury Mass Fractions (< 10 ng g‐1) in Crystalline Rocks: Direct Mercury Analyser Versus Cold Vapour‐Atomic Fluorescence Spectroscopy

Elemental mercury (Hg) is routinely determined in crystalline rocks with mass fractions lower than 10 ng g-1 by thermal decomposition using Direct Mercury Analyzer (DMA-80) or Lumex RA-915+ (equipped with a PYRO-915+ attachment) instruments, both based on atomic absorption spectroscopy. However, 223 analyses over the course of one year with DMA-80 and cold vapour-atomic fluorescence spectroscopy (CV-AFS) on three reference materials (RMs) and six crystalline rocks (granite, diorite, gabbro, spinel peridotite, phlogopite-rich peridotite, and sulfide-rich orthogneiss) from the exposed transcrustal section of the Ivrea-Verbano Zone and upper crustal Serie dei Laghi unit (western Alps, Italy) reveal that rock analyses using the DMA-80 are variably affected by different internal and external biases when Hg mass fractions are below 10 ng g-1. Conversely, CV-AFS analyses are more precise, providing homogenous and repeatable results, even at ultra-low Hg mass fractions (< 1 pg g-1). Furthermore, CV-AFS analyses show that gabbro and spinel peridotite powders roasted for analysis by DMA-80 still contain ~ 0.6 to ~ 1.4 ng g-1 of Hg, implying inefficient release of Hg from basic/ultrabasic lithologies. Therefore, we recommend the use of CV-AFS for Hg measurements in crystalline rocks. We also propose a new Hg reference value of 3.9 ± 1.5 ng g-1 for the GSJ granodiorite reference material JG-1a

Transformative Knowledge for an era of Planetary Urbanization? Questioning the role of social sciences and humanities from an interdisciplinary perspective

This document reports the main outputs of the world café discussion held during the seminar ‘Transformative Knowledge for an Era of Planetary Urbanization’ at the Institute of the Social Sciences of the University of Lisbon (ICS-ULisboa) on 10 July 2017 – an event convened by the COST Action INTREPID, the research group Environment, Territory and Society of ICS-ULisboa, and the Young Academics Network of AESOP.info:eu-repo/semantics/publishedVersio

Zero Knowledge Protocols and Signatures from the Restricted Syndrome Decoding Problem

The Restricted Syndrome Decoding Problem (R-SDP) cor- responds to the Syndrome Decoding Problem (SDP) with the additional constraint that entries of the solution vector must live in a desired sub- set of a finite field. In this paper we study how this problem can be applied to the construction of signatures derived from Zero-Knowledge (ZK) proofs. First, we show that R-SDP appears to be well suited for this type of applications: almost all ZK protocols relying on SDP can be modified to use R-SDP, with important reductions in the communication cost. Then, we describe how R-SDP can be further specialized, so that solutions can be represented with a number of bits that is slightly larger than the security parameter (which clearly provides an ultimate lower bound), thus enabling the design of ZK protocols with tighter and rather competitive parameters. Finally, we show that existing ZK protocols can greatly benefit from the use of R-SDP, achieving signature sizes in the order of 7 kB, which are smaller than those of several other schemes ob- tained from ZK protocols. For instance, this beats all schemes based on the Permuted Kernel Problem (PKP), almost all schemes based on SDP and several schemes based on rank metric problems

Unveiling pyroelectricity in ferroelectric planar capacitors with area-selective wet etched hafnium zirconium oxide: from ab initio and multiphysics simulations to experiments

In this work, a systematic approach aimed at investigating and validating a novel way of realizing pyroelectric harvesting is presented. Generating a direct-current (dc) signal through a temperature gradient within a less than 7 nm-thick ferroelectric zirconium-doped hafnium oxide (HZO) nano-film, embedded in planar interdigitated capacitors on high-resistivity silicon, is a new, simple, effective, and reproducible solution. Temperature-related structural modifications in HZO are first simulated using advanced ab initio calculations. Then, rigorous multiphysics simulations of the final devices provide insight into the expected performance of the pyroelectric harvester, as a function of temperature, contact area, and crystal orientation, showing a maximum open-circuit voltage of up to 900 mV. The fabrication of the harvesters involves the area-selective wet etching of the HZO layer to retain it exclusively in between the fingers of each capacitor. This choice maximizes the pyroelectric effect (which strongly depends on the area) and represents a new paradigm in the development of HZO-based electronics, which are conventionally built on ferroelectric continuous films. Experimental validation at both low frequencies and microwaves confirms the pyroelectric effect, exhibiting a significant increase in the output current for higher temperature gradients, and a generated dc voltage of several hundred millivolts