Silica thin-films from perhydropolysilazane for the protection of ancient glass

Silica coatings from polysilazane precursors were prepared to protect ancient glass from weathering. Polysilazane can be converted to silica by simple exposition to air or basic vapours and the properties of the synthesized film make this precursor a valuable choice to obtain solid, crack-free, highly adhesive and protective coatings. The coating is prepared starting from a Perhydropolysilazane precursor (20% PHPS in n-butyl ether) that allows to achieve high-quality thin-films of silica at room temperature. The obtained films are uncoloured, even in absence of strong heat-treatment. Perhydropolysilazane (PHPS) is a polymer of [-SiH2-NH-SiH2-]n units. When deposited on a soda-lime microscope slide, it reacts with atmospheric moisture (Si-H and Si-NH bonds are hydrolysed to Si-O) and a silica film is produced. The conversion to silica is completed in about 2.5 hours, using vapours of a 10 mol L-1 ammonia solution. The reaction is promoted with the application of a weak heat-treatment (45-50 \ub0C), achievable using as heater a common tungsten filament lamp. The reaction of PHPS with atmospheric moisture produces a migration phenomenon of the mobile ions from the soda-lime glass to the film (in particular sodium, calcium and magnesium). The characteristics of the migration process vary according to the concentration of the precursor solution and the thickness of the film. Laboratory samples have been investigated by optical microscopy and surface techniques: XPS and SIMS. Preliminary evidences, obtained through the laser scanning confocal microscope (LEXT), on the application of such coatings at the surface of ancient stained glass are also discussed

A simple linear time algorithm for the locally connected spanning tree problem on maximal planar chordal graphs

A locally connected spanning tree (LCST) T of a graph G is a spanning tree of G such that, for each node, its neighborhood in T induces a connected sub- graph in G. The problem of determining whether a graph contains an LCST or not has been proved to be NP-complete, even if the graph is planar or chordal. The main result of this paper is a simple linear time algorithm that, given a maximal planar chordal graph, determines in linear time whether it contains an LCST or not, and produces one if it exists. We give an anal- ogous result for the case when the input graph is a maximal outerplanar graph

Perspectives on the regulation of search engine algorithms and social networks: The necessity of protecting the freedom of information

The paper studies how the paradigm of the freedom of information has changed by the advent of the Internet and whether new forms of regulation of the Internet media are necessary. The paper focuses on two different issues: on one side, the importance of the algorithms and of search engines in the field of the press is analysed; on the other side, the central role played by social networks in the spread of news is examined. These phenomena are affecting the world of journalism by impacting on one of the most important element of the constitutional-democratic order: the freedom of information and the press as “watchdog of democracy”. The algorithms developed by search engines decide what type of news we “receive” when we use the search string for a query, and the social networks are going to become the global newsstand of news in the near future. The research question of this paper is whether and how these two phenomena should be regulated according to the Italian paradigm of the freedom of information. In the first part of the paper, in section 2, the innovations and transformations of the world of information that are related to the advent of the Internet are highlighted. Next, in section 3, the constitutional principles of the media sector are briefly analysed, in order to develop a systemic approach to the framing of the new media of the Internet. In the second part, in section 4, the characteristics of search engines and social networks are explored, and the requirement that they are classified as ‘means of distribution of news’ (i.e. as media), with the necessary regulatory consequences, is stressed. In the development of this analysis, comparisons with American doctrine and case law cannot be avoided, because of the remarkable sensitivity in the US to the reality of the Internet and its problems. In this paper a fairly simple solution is proposed concerning the spreading of news by the new media: 1) search engines should show and clarify the algorithms they use to select the news they propose to users; in this way, readers can choose what type of editorial criteria (meaning algorithms) they use, by choosing what type of search engines they use; and 2) social networks should guarantee that fake news on their platforms will be rectified/corrected

Some aspects of Analysis on symmetric spaces and homogeneous trees: from Radon transform to Bergman spaces

The thesis is focused on the Analysis on two classes of non Euclidean spaces: the symmetric spaces of the noncompact type and the homogeneous trees. I first solve in both the settings the problem of the Unitarization of the Radon transform. The last chapter is devoted to the study of the harmonic Bergman spaces on homogeneous trees

Ultrathin iron oxide films on Ru(0001)

Tesis doctoral inédita leída en la Universidad Autónoma de Madrid, Facultad de Ciencias, Departamento de Física Aplicada. Fecha de lectura: 11-07-2014In this dissertation the growth and properties of ultrathin iron oxides lms on ruthenium have been investigated by means of di raction, microscopy and spectroscopy techniques. The systems studied have been prepared in-situ using molecular beam epitaxy and oxygen-assisted molecular beam epitaxy. We begin with the preparation of ultrathin FeO lms following their growth on Ru(0001) by low-energy electron microscopy and scanning tunneling microscopy. After a brief spectroscopic and structural characterization, the role of the experimental parameters, i.e., temperature and oxygen pressure, in the growth mechanism has been discussed. Then, the preparation of a bi-component iron oxide lm on ruthenium has been presented. This system, composed by an FeO wetting layer and perfect magnetite crystals, has been characterized by means of structural and spectroscopic measurements. Focusing on these magnetite crystals, we have shown that selecting adequately the experimental conditions they can maintain their stability even when their thickness is reduced at the nanometer scale. Additionally, we have characterized the magnetic properties of these crystals using synchrotron radiation-based techniques, and we have found that they exhibit well-de ned magnetic domains proving that ferrimagnetism can be retained in these 1 nm thick magnetite lms. Next, the oxidation of this bi-component lm by NO2 has been studied. The chemical transformation of the initially-grown lm takes place producing a di erent bi-component lm, formed by an hematite wetting layer and maghemite crystals. We have been able to propose an oxidation mechanism consisting in a topotactic transformation experienced by the iron cations. Thus, by means of a choice of the experimental parameters, the preparation of di erent bi-component iron oxides in ultrathin lm form on the same substrate can be achieved. Finally, we reported the design and construction of an ultra high vacuum integral lowenergy electron M ossbauer spectrometer aimed at the chemical, structural and magnetic characterization of Fe-containing surfaces. The proposed design together with the optimization procedures have been presented and discussed. The rst results on bicomponent iron oxide lms suggest that this unconventional M ossbauer spectroscopy is suitable for measurements of iron oxide nanostructuresLos óxidos de hierro son considerados materiales prometedores de cara a futuros desarrollos en diferentes campos tecnológicos como la catálisis, la biología, o la microelectrónica. A pesar de ser compuestos ampliamente estudiados, está demostrado que las propiedades de volumen se ven fuertemente modificadas en superficie o afectadas por la reducción de sus dimensiones a escala nanométrica. Para favorecer un correcto desarrollo de los dispositivos en el cual estos materiales están involucrados, es de crucial importancia obtener un conocimiento detallado de cómo las propiedades químico{físicas de los óxidos de hierro dependen de los fenómenos superficiales y de los efectos de baja dimensionalidad. De acuerdo con esto, el objetivo principal del trabajo presentado es el estudio de como se modifican las propiedades de los óxidos de hierro cuando están preparados en capas ultra-delgadas. Inicialmente mediante técnicas de microscopia, espectroscopia y difracción, hemos investigado películas de FeO preparadas mediante la técnica de epitaxia de haces moleculares, tanto estandar como asistida por oxígeno molecular. Hemos detectado que, dependiendo de las condiciones experimentales utilizadas, la morfología de las películas crecidas sobre Ru(0001) se modifica, dejando inalterada la naturaleza químico{física del material. Realizando estudios con microscopía de electrones de baja energía hemos podido investigar y proponer un modelo que describe la dependencia del mecanismo de crecimiento de las películas de FeO con la presión de oxígeno y la temperatura del substrato. En una segunda etapa, hemos crecido películas de óxidos de hierro compuestas de una capa continua de FeO sobre la cual se ha identificado la nucleación de cristales de magnetita. Hemos centrado nuestra atención en los cristales de magnetita y, combinando técnicas de microscopia, espectroscopia y difracción hemos observado como dichos cristales permanecen estables aunque su espesor se mantenga muy próximo a un nanómetro. Ademáss, se han estudiado las propiedades magnéticas de estos cristales nanométricos mediante dicroísmo magnético circular de rayos X, demostrando que el carácter ferrimagnético se mantiene a pesar de ser extremadamente delgados. En una tercera etapa, los cristales de magnetita crecidos sobre una wetting layer de FeO se han expuestos a un gas reactivo (NO2) y se ha estudiado el mecanismo de oxidación utilizando las técnicas mencionadas anteriormente. Se ha detectado que la fase FeO se oxida dando lugar a una wetting layer compuesta por hematita mientras los cristales de magnetita evolucionan formando maghemita. Los distintos procesos de oxidación se han explicado proponiendo un mecanismo topotáctico en el cual están involucrados los cationes de hierro de las diferentes estructuras. En particular, hemos podido describir como selecionando adecuadamente parámetros experimentales es posible preparar una película ultra-delgada de óxidos de hierro de distinta composición sobre el mismo substrato metálico. Finalmente, hemos presentado y discutido la construcción y la puesta en marcha de un espectrómetro Mossbauer para la detección de electrones de baja energía. Dicha técnica basada en el efecto Mossbauer proporciona información químico-física con sensibilidad superficial de nanoestructuras que contengan hierro. Hemos presentados los primeros resultados obtenidos de la caracterización de películas ultra-delgadas de óxido de hierro descrita anteriormente, demostrando así la extrema versatilidad de esta técnica en los estudio de nano-estructuras

Design of sustainable agricultural buildings. A case study of a wine cellar in Tuscany, Italy

This research concerns the design of an agricultural building with a high degree of sustainability, located in a farm in the south of the Tuscany region, Italy. The building, intended mainly as a wine cellar, offers innovative construction solutions of high deconstructability and has features of low environmental impact, economic competitiveness and constructive simplicity. In particular, the design of the basement cellar involves the use of gabions and stones for the realization of the foundations, the ground retaining walls and all other bearing walls. A different solution is adopted for the external wall which remains entirely above ground. It is also made by gabions, but it is externally covered with a coat of straw bales and is plastered with clay or lime. The roof-bearing structure is made of steel beams and galvanized steel sheets. A layer of fertile soil is arranged on the roof to form a green roof system. This research aims to spread the design criteria of deconstructable buildings, based on the use of natural materials with low environmental and economic impact. Where it is not possible to employ natural materials, reusable or recyclable materials are used

New solutions for horse shelters to connect to the equestrian paths

A rational and modern network of riding trails involves the building of specific structures for the horses according to the new needs of equestrian tourists. These shelters require appropriate technical models that today cannot be found easily in the Italian or foreign literature. Over the years this gap has led to the development of the practice “do it yourself”, following old techniques of construction, not able to meet the new demands of the market of horse tourism. This research has highlighted two different solutions that can meet the needs of tourists riding today, in accordance with the laws about the construction and the health part. These structures have been designed observing the principles of low impact, low cost, easy installation, complete reuse. Two kinds of structures have been planned. Temporary stay horse shelter: building to put in resting places of interest along the path (historic villages, monasteries, etc.), where it is possible to arrange the horses for a few hours and allow to the riders to make a careful visit of places of interest. Overnight stay horse shelter: structure to put in particular points where horses and riders can spend the night. A new type of horse barn with annexed feed storage and saddle room. The structure is dynamic, due to the possibility to change quickly the position of the horses (max 8 places)

Scalable Byzantine Reliable Broadcast

Byzantine reliable broadcast is a powerful primitive that allows a set of processes to agree on a message from a designated sender, even if some processes (including the sender) are Byzantine. Existing broadcast protocols for this setting scale poorly, as they typically build on quorum systems with strong intersection guarantees, which results in linear per-process communication and computation complexity. We generalize the Byzantine reliable broadcast abstraction to the probabilistic setting, allowing each of its properties to be violated with a fixed, arbitrarily small probability. We leverage these relaxed guarantees in a protocol where we replace quorums with stochastic samples. Compared to quorums, samples are significantly smaller in size, leading to a more scalable design. We obtain the first Byzantine reliable broadcast protocol with logarithmic per-process communication and computation complexity. We conduct a complete and thorough analysis of our protocol, deriving bounds on the probability of each of its properties being compromised. During our analysis, we introduce a novel general technique that we call adversary decorators. Adversary decorators allow us to make claims about the optimal strategy of the Byzantine adversary without imposing any additional assumptions. We also introduce Threshold Contagion, a model of message propagation through a system with Byzantine processes. To the best of our knowledge, this is the first formal analysis of a probabilistic broadcast protocol in the Byzantine fault model. We show numerically that practically negligible failure probabilities can be achieved with realistic security parameters