159 research outputs found
A branched covering of degree of the sphere with a completely invariant indecomposable continuum
We construct a branched covering of degree of the sphere having a
completely invariant indecomposable continuum . The existence of such an
object is not known for rational maps of the sphere
The growth rate inequality for Thurston maps with non hyperbolic orbifolds
Let be a continuous map of degree , , and let
denote the number of fixed points of . We show that if is a
Thurston map with non hyperbolic orbifold, then either the growth rate
inequality holds for or
has exactly two critical points which are fixed and totally invariant
Study of the effects of salt crystallisation on degradation of limestone rocks
Salt crystallization is widely recognized as a cause of deterioration of porous building materials. In particular, the crystallization pressure of salt crystals growing in confined pores is found to be the main cause for damage. The aim of this study is to better understand the degradation of porous rocks induced by salt crystallisation and correlate such processes with the intrinsic characteristics of materials. With this intend, an experimental salt weathering simulation has been carried out on two limestones widely used in the Baroque architecture of eastern Sicily. A systematic approach including petrographic, porosimetric and colorimetric analyses, was used to evaluate the correlation among salt crystallisation, microstructural and chromatic variations of limestone. Results showed a quite different resistance of the two limestones to salt damage, and this was found to be strongly dependent on their pore structure and textural characteristics
Comparative study of protective coatings for the conservation of Urban Art
Contemporary mural paintings are complex artworks for several reasons, including the heterogeneity of the materials used to make them, and the different types of substrate on which the painting layers can be applied. Currently we are focused on a technical-scientific research aimed to solve the issues related to the long-term care and maintenance of murals, by evaluating the performance of several protective coatings applied on these artworks. This paper deals with a preliminary experimentation aimed to: (a) study the interaction of antigraffiti products on common synthetic paints; (b) test the effectiveness and efficiency of several commercial products used as antigraffiti; (c) define of the best procedure to remove vandalism spray from a coated surface, without damaging the underlying painting layers. Tests have been carried out on laboratory specimens and the performances of different antigraffiti agents have been evaluated by optical and electron microscope observations, as well as by colorimetric measurements
Archaeometric approach for the study of mortars from the underwater archaeological site of Baia (Naples) Italy: Preliminary results
This work was aimed to evaluate the features of mortar samples taken from the underwater
archaeological area of Baia (Naples, Italy), an important site, where the remains of the
ancient Roman city of Baiae and Portus Iulius are submerged after bradyseism events, started
from 4th century AD. Several architectural structures are still preserved into the submerged
environment, such as: luxurious maritime villas, imperial buildings, private houses, thermae,
tabernae and warehouses. In particular, some samples were collected from the masonry walls
belonging to a building of the underwater area called Villa a Protiro. A first archaeometric
approach has been applied to analyse twelve archaeological mortars samples in order to define:
textural features, chemical composition and raw materials used for their production. For
this purpose different analytical methods were used, such as, polarizing optical microscope
(POM) and scanning electron microscopy (SEM-EDS).This work was financially supported by
national national research project “COMAS”
(Planned COnservation, “in situ”, of underwater
archaeological artifacts), funded by the Italian
Ministry of Education, Universities and
Research (MIUR).Peer reviewe
New insights to assess the consolidation of stone materials used in built heritage: the case study of ancient graffiti (Tituli Picti) in the archaeological site of Pompeii
Tituli Picti are an ancient form of urban graffiti very common in the archaeological site of Pompeii (Naples, South—Italy). They are generally made of red pigments applied on walls of Campanian ignimbrite. This paper deals with a scientific investigation aimed to their conservation. This is a challenging task since it requires a multidisciplinary approach that includes restorers, archaeologists and conservation scientists. The study has provided suggestions on the proper way to conserve Tituli Picti over time. In the present work, several specimens of Campanian ignimbrite were painted with red earth pigment; lime and Arabic gum have been used as binders as well. Such painted stones were treated with three consolidants: a suspension of reactive nanoparticles of silica, ethyl silicate and an acrylic microemulsion. Treated and untreated specimens were subjected to thermal aging, artificial solar radiation and induced crystallization decay. It has been assessed the colorimetric variations induced by treatments. Moreover, the micromorphologic features of the consolidated surfaces have been highlighted by means of electron microscope observations. The scotch tape test allowed to compare the superficial cohesion induced by the three used products. According to the results, ethyl silicate seems to represent the most successful product
Polyphenols and ischemic stroke: Insight into one of the best strategies for prevention and treatment
Ischemic stroke (IS) is still among the leading causes of death and disability worldwide. The pathogenic mechanisms beyond its development are several and are complex and this is the main reason why a functional therapy is still missed. The beneficial effects of natural compounds against cardiovascular diseases and IS have been investigated for a long time. In this article, we reviewed the association between the most studied polyphenols and stroke protection in terms of prevention, effect on acute phase, and rehabilitation. We described experimental and epidemiological studies reporting the role of flavonols, phenolic acid, and stilbens on ischemic mechanisms leading to stroke. We analyzed the principal animal models used to evaluate the impact of these micronutrients to cerebral blood flow and to molecular pathways involved in oxidative stress and inflammation modulation, such as sirtuins. We reported the most significant clinical trials demonstrated as the persistent use of polyphenols is clinically relevant in terms of the reduction of vascular risk factors for IS, such as Atrial Fibrillation. Interestingly, different kinds of polyphenols provide brain protection by activating different pathways and mechanisms, like inducing antithrombotic effect, such as Honokiol. For this reason, we discussed an appropriate integrative use of them as a possible therapeutic alternative against stroke
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