Nonsmooth bifurcations in a piecewise-linear model of the Colpitts oscillator

This paper deals with the implications of considering a first-order approximation of the circuit nonlinearities in circuit simulation and design. The Colpitts oscillator is taken as a case study and the occurrence of discontinuous bifurcations, namely, border-collision bifurcations, in a piecewise-linear model of the oscillator is discussed. In particular, we explain the mechanism responsible for the dramatic changes of dynamical behavior exhibited by this model when one or more of the circuit parameters are varied. Moreover, it is shown how an approximate one-dimensional (1-D) map for the Colpitts oscillator can be exploited for predicting border-collision bifurcations. It turns out that at a border collision bifurcation, a 1-D return map of the Colpitts oscillator exhibits a square-root-like singularity. Finally, through the 1-D map, a two-parameter bifurcation analysis is carried out and the relationships are pointed out between border-collision bifurcations and the conventional bifurcations occurring in smooth system

Carbon-based nanomaterials

2014 - 2015New layered carbon-based materials were prepared and exhaustively characterized exploiting different characterization techniques, such as thermogravimetry (TGA), differential thermal calorimetry (DSC), Fourier transform infrared (FTIR) and wide angle X-ray diffraction (WAXD). Pristine graphite (G) with high surface area and carbon black (CB) samples with different surface areas were selected as starting materials to prepare the corresponding oxidized samples, i.e. graphite oxide (GO) and carbon black oxide (oCB), with the Hummers’ method. Thanks to the strong hydrophilicity and to the lamellar structure of oxidized carbon-based materials, a rich intercalation chemistry is permitted. In fact, after treatments of GO and oCB by strong basis, ordered intercalation compounds have been obtained, not only if the starting material is crystalline like graphite oxide, but also if it is completely amorphous like oxidized carbon black. Starting basified GO, free-standing papers can be obtained by vacuum filtration, as well as by casting procedure, of colloidal dispersions of graphene oxide sheets. The use of basified GO leads to more flexible, solvent resistant and thermally stable GO papers. Spectroscopic analyses of the obtained papers have been conducted aiming to a possible rationalization of the observed behavior. [edited by author]Per questo lavoro di tesi di dottorato, sono stati preparati nuovi nanomateriali basti su carbonio ed esaustivamente caratterizzati con tecniche quali termogravimetria (TGA), calorimetria a scansione differenziale (DSC), spettroscopia infrarossa (FT-IR) e diffrazione dei razzi X (WAXD). I materiali di partenza utilizzati per questo lavoro di tesi, sono stati la grafite ad alta area superficiale e carbon black con differenti valori di area superficiale, al fine di ottenere i corrispondenti materiali ossidati quali ossido di grafite (GO) e carbon black ossidato (oCB). Il metodo utilizzato per le ossidazioni dei suddetti starting materials è quello di Hummers. Grazie alla forte idrofilicità ed alla struttura lamellare posseduta dai materiali carboniosi ossidati, è possibile ottenere svariati composti di intercalazione trattando il GO (cristallino) e l’oCB(amorfo) con basi forti e con conseguente funzionalizzazione ionica con cationi di natura organica. Inoltre, partendo da dispersioni di GO basificato, sono stati ottenuti fogli di ossido di grafite e di grafene mediante filtrazione e/o per lenta evaporazione del solvente. Utilizzando una base nella procedura di ottenimento dei cosiddetti fogli di ossido di grafite/grafene, sono stati preparati campioni free-standing con elevata flessibilità, resistenza ai solventi e alle alte temperature. [a cura dell'autore]XIV n.s

Nonlinear analysis of the Colpitts oscillator with applications to design

This paper reports a methodological approach to the analysis and design of sinusoidal oscillators based on bifurcation analysis. The simple Colpitts oscillator is taken as an example to demonstrate this nonlinear approach for both the nearly sinusoidal and chaotic modes of operation. In particular, it is shown how regular and irregular (chaotic) oscillations can be generated, depending on the circuit parameters

A general method to predict the amplitude of oscillation in nearly-sinusoidal oscillators

In this paper, a general methodology for predicting the amplitude of oscillation in nearly sinusoidal oscillators is presented. The method relies on the recently proposed projection technique for the computation of the center manifold and on the Hopf normal form theory to approximate the corresponding limit cycle in state space. The Colpitts oscillator is selected as a case study and, for this circuit, a closed-form expression for the amplitude of oscillation is derived as a function of the circuit parameters

Shooting down the price: Evidence from Mafia homicides and housing prices

In this paper, we estimate the effect of the homicides by the Camorra, the Neapolitan Mafia, on housing prices in Naples. The study develops on a unique panel data set at the administrative district level for the period 2002–2018 of geo-localized homicides involving innocent victims (denoted as IVH), which are treated as exogenous shocks that negatively affect housing demand. We find that the occurrence of such homicides causes a decrease in housing prices in the range of 2.5–3.8 percentage points. This effect decreases with the distance from an IVH and over time. These results are robust to the utilization of different econometric specifications and to the considerations of possible confounding factors such as other types of Camorra homicides

Karst of Sicily and its conservation

In Sicily, karst is well developed and exhibits different types of landscapes due to the wide distribution of soluble rocks in different geological and environmental settings. Karst affects both carbonate rocks, outcropping in the northwest and central sectors of the Apennine chain and in the foreland area, and evaporite rocks, mainly gypsum, that characterize the central and the southern parts of the island. The carbonate and gypsum karsts show a great variety of surface landforms, such as karren, dolines, poljes, blind valleys, and fluvio-karst canyons, as well as cave systems. Karst areas in Sicily represent extraordinary environments for the study of solution forms. In addition, they are of great environmental value because they contain a variety of habitats that hold species of biogeographic significance. Unfortunately, karst areas are increasingly threatened by human activity, mainly in the form of grazing and other agricultural practices, wildfires, quarrying, urbanization, building of rural homes, and infrastructure development. The value of karst features has been recognized by the Sicilian Regional Government since 1981 when it enacted laws to create several nature reserves to preserve the peculiar karst landscapes, including caves. At present, the state of conservation of karst areas in Sicily may be considered to be at an acceptable level, yet numerous issues and difficulties need to be overcome for the effective protection and enhancement of karstlands

Shooting Down the Price: Evidence from Mafia Homicides and Housing Market Volatility

In this paper we estimate the effect of the homicides by the Camorra, the Neapolitan Mafia, on housing prices in Naples. The study develops on a unique panel dataset at the administrative district level for the period 2002-2018 of geo-localized homicides involving innocent victims (denoted as IVH ), which are treated as exogenous shocks that negatively affect housing demand. We find that the occurrence of such homicides causes a decrease in housing prices in the range of 2.5 − 3.8 percentage points. This effect decreases with the distance from an IVH and over time. These results are robust to the utilization of different econometric specifications and to the considerations of possible confounding factors such as other types of textitCamorra homicides

Vision-Based Terrain Relative Navigation on High-Altitude Balloon and Sub-Orbital Rocket

We present an experimental analysis on the use of a camera-based approach for high-altitude navigation by associating mapped landmarks from a satellite image database to camera images, and by leveraging inertial sensors between camera frames. We evaluate performance of both a sideways-tilted and downward-facing camera on data collected from a World View Enterprises high-altitude balloon with data beginning at an altitude of 33 km and descending to near ground level (4.5 km) with 1.5 hours of flight time. We demonstrate less than 290 meters of average position error over a trajectory of more than 150 kilometers. In addition to showing performance across a range of altitudes, we also demonstrate the robustness of the Terrain Relative Navigation (TRN) method to rapid rotations of the balloon, in some cases exceeding 20 degrees per second, and to camera obstructions caused by both cloud coverage and cords swaying underneath the balloon. Additionally, we evaluate performance on data collected by two cameras inside the capsule of Blue Origin's New Shepard rocket on payload flight NS-23, traveling at speeds up to 880 km/hr, and demonstrate less than 55 meters of average position error.Comment: Published in 2023 AIAA SciTec

Analysis of single comments left for bioRxiv preprints till September 2019

While early commenting on studies is seen as one of the advantages of preprints, the type of such comments, and the people who post them, have not been systematically explored. We analysed comments posted between 21 May 2015 and 9 September 2019 for 1983 bioRxiv preprints that received only one comment on the bioRxiv website. The comment types were classified by three coders independently, with all differences resolved by consensus. Our analysis showed that 69% of comments were posted by non-authors (N = 1366), and 31% by the preprints’ authors themselves (N = 617). Twelve percent of non-author comments (N = 168) were full review reports traditionally found during journal review, while the rest most commonly contained praises (N = 577, 42%), suggestions (N = 399, 29%), or criticisms (N = 226, 17%). Authors’ comments most commonly contained publication status updates (N = 354, 57%), additional study information (N = 158, 26%), or solicited feedback for the preprints (N = 65, 11%). Our results indicate that comments posted for bioRxiv preprints may have potential benefits for both the public and the scholarly community. Further research is needed to measure the direct impact of these comments on comments made by journal peer reviewers, subsequent preprint versions or journal publications