Multi-technique characterization of glass mosaic tesserae from Villa di Teodorico in Galeata (Italy)

Several glass mosaic tesserae were found during the archeological excavations at the Villa di Teodorico in Galeata (Forl\uec-Cesena, Emilia Romagna, Italy), dated to early sixth century AD. This work reports the results of an archeometrical investigation realized through a multi-technique approach on 16 tesserae. The aims of the study were the determination of the glass composition, the characterization of coloring and opacifying agents, and the definition of the technological processes involved. The glass matrix and the dispersed crystallites were characterized in detail through micro-Raman spectroscopy, field emission scanning electron microscopy with energy-dispersive X-ray spectroscopy, and X-ray powder diffraction analyses. Micro-Raman spectroscopy was proven to be very effective in the analysis of complex objects, providing information on the structure and composition of the glass and on the nature of the opacifying agents and the crystalline colorants. UV\u2013visible\u2013NIR diffuse reflectance spectrophotometry with optic fibers was helpful to identify the metal ions used as chromophores. The different hues were obtained by means of dispersed ions as well as crystalline compounds and metal nanoparticles. A large variety of opacifying agents was detected. Results were compared with data of contemporary mosaics within the same geographical area

Cathodoluminescence, Raman and scanning electron microscopy with energy dispersion system mapping to unravel the mineralogy and texture of an altered Ca-Al-rich inclusion in Renazzo CR2 carbonaceous chondrite

An altered fluffy type A Ca-Al-rich inclusion in the CR2 Renazzo carbonaceous chondrite was examined by combined Raman, scanning electron microscopy with energy dispersion system (SEM-EDS) and cathodoluminescence (CL) mapping. Blue CL at 450 nm and orange emission at 600 nm were related to anorthite and calcite, respectively. Raman spectra were highly fluorescent, and only the stronger peaks of anorthite, clinopyroxene and calcite were observed. Raman-induced fluorescence emission was measured using the 632-nm Raman laser source, up to 850 nm, and used to chart the mineral phases. A fluorescence structured peak at 690 nm, split in three subpeaks at 678, 689 and 693 nm, was found; it is likely related to the fluorescence emission of Cr3+ from a fassaitic pyroxene in anorthite. Secondary pyroxene in the Wark–Lovering rim does not show the peak at 690 nm; the different fluorescence emission from the secondary rim and the pyroxene patches within anorthite could be a marker to spot the primary pyroxene. From combined imaging, the events in the altered chondrite could be sequenced. Starting from a pristine assemblage of spinel and melilite, with little fassaite, several alteration episodes occurred. Alteration in secondary anorthite, which could be mapped by the blue CL emission at 450 nm, was followed by alkalization, with rims of sodalite and nepheline, and subsequent formation of secondary clinopyroxene, encircling the inclusion. Widespread calcite alteration, present also in the matrix between chondrules, was the last recorded event

An in-and-out-the-lab Raman spectroscopy study on street art murals from Reggio Emilia in Italy

The street art murals ‘The Big Mother’ by Gola Hundun, the ‘Big Sacral Bird’ by Kenor, the ‘Oriental Carpet” by H101 and “The Economy Subdues You” by Zosen, belonging to the Cooperative Popular Houses of Mancasale and Coviolo in Reggio Emilia (Italy), were investigated by the use of various mobile Raman spectrometers coupled to different lasers and by micro-Raman spectroscopy on selected samples. The study was made necessary by the evident fading of many colours, despite the young age of the paintings, realized in 2010. The first step of the investigation, realized by the on-site campaign, was the identification of the materials, and in particular of the dyes. The main chromophores were identified as polycyclic, monoazo- and disazo- organic pigments, with inorganic compounds as bismuth vanadate (BiVO4) together with the extensive presence of rutile (TiO2). The second step was devoted to the study of the degradation mechanism affecting the colourful layers of the murals. It required the use of laboratory micro-spectrometers and was carried out on a reduced set of samples, selected during the in-situ campaign. This combination of on-site and laboratory Raman spectroscopy allowed the obtaining of the complete identification of the palette used by the different artists in a single day of measurements, in a complete non-destructive day. In addition, it was possible to minimize the number of samples required for the study of the degradation process. Graphical abstract: [Figure not available: see fulltext.

Techno-economic analysis of a solar thermal plant for large-scale water pasteurization

Water pasteurization has the potential to overcome some of the drawbacks of more conventional disinfection techniques such as chlorination, ozonation and ultraviolet radiation treatment. However, the high throughput of community water systems requires energy-intensive processes, and renewable energy sources have the potential to improve the sustainability of water pasteurization plants. In case of water pasteurization by solar thermal treatment, the continuity of operation is limited by the intermittent availability of the solar irradiance. Here we show that this problem can be addressed by a proper design of the plant layout, which includes a thermal energy storage system and an auxiliary gas boiler. Based on a target pasteurization protocol validated by experiments, a complete lumped-component model of the plant is developed and used to determine the operating parameters and size of the components for a given delivery flow rate. Finally, we report an economic analysis of the proposed plant layout, which allows its optimization for different scenarios based on two design variables, namely the solar multiple and the duration of the thermal energy storage. Based on the analyzed cases, it is found that the proposed plant layouts may yield a unit cost of water treatment ranging from ≈32 EUR-cents m−3 to ≈25 EUR-cents m−3

Techno-economic analysis of a solar thermal plant for large-scale water pasteurization

Water pasteurization has the potential to overcome some of the drawbacks of more conventional disinfection techniques such as chlorination, ozonation and ultraviolet radiation treatment. However, the high throughput of community water systems requires energy-intensive processes, and renewable energy sources have the potential to improve the sustainability of water pasteurization plants. In case of water pasteurization by solar thermal treatment, the continuity of operation is limited by the intermittent availability of the solar irradiance. Here we show that this problem can be addressed by a proper design of the plant layout, which includes a thermal energy storage system and an auxiliary gas boiler. Based on a target pasteurization protocol validated by experiments, a complete lumped-component model of the plant is developed and used to determine the operating parameters and size of the components for a given delivery flow rate. Finally, we report an economic analysis of the proposed plant layout, which allows its optimization for different scenarios based on two design variables, namely the solar multiple and the duration of the thermal energy storage. Based on the analyzed cases, it is found that the proposed plant layouts may yield a unit cost of water treatment ranging from ≈32 EUR-cents m-3 to ≈25 EUR-cents m-3

Large-scale modelling of neuronal systems

The brain is, without any doubt, the most complex system of the human body. Its complexity is also due to the extremely high number of neurons, as well as the huge number of synapses connecting them. Each neuron is capable to perform complex tasks, like learning and memorizing a large class of patterns. The simulation of large neuronal systems is challenging for both technological and computational reasons, and can open new perspectives for the comprehension of brain functioning. A well-known and widely accepted model of bidirectional synaptic plasticity, the BCM model, is stated by a differential equation approach based on bistability and selectivity properties. We have modified the BCM model extending it from a single-neuron to a whole-network model. This new model is capable to generate interesting network topologies starting from a small number of local parameters, describing the interaction between incoming and outgoing links from each neuron. We have characterized this model in terms of complex network theory, showing how this learning rule can be a support for network generation

High-pressure Raman spectroscopy on low albite

The pressure dependence of the Raman spectrum of low albite, NaAlSi3O8, has been investigated from 0.0001 to 10.4 GPa, at room temperature, on a single crystal compressed hydrostatically in a diamond anvil cell. The Raman vibrational features move to higher wavenumbers \u3c5i with increasing pressure, due to the decrease in the unit-cell volume corresponding to a drastic shrinkage of the framework. The slopes \u394\u3c5i/\u394P of the four investigated bending modes (i.e. at 478, 507, 578 and 815 cm 121, at 0.0001 GPa) show evident changes at ~6.5 and ~8.5 GPa. This behaviour may be ascribed, in the absence of phase transitions, to the evolution of the compressional mechanisms at the atomic scale found in previous high-pressure studies on albite (mainly by X-ray diffraction), through a model based on tilts of rigid tetrahedra. The Raman data of this study allowed also to bracket the pressure range in which the occurrence of the first change in the compressional behaviour was found by X-ray diffraction

Aging of PLS-glass: Study of the alteration phenomena.

The wood ash-based glass (PLS, potash-lime-silica), employed for medieval cathedral windows in Northern Europe since 1000 A.D., is particularly sensitive to the alteration phenomena. Three PLS medieval-like glass were produced with different K2O content and characterized by FT-IR and Raman spectroscopy. Aging experiments were carried out by sulfuric acid and water, checking, in this last case, the pH over time. The weight loss and the alteration layer thickness were measured and the interacting solutions were analyzed through AAS. Raman maps were recorded on the altered glass cross sections. Changes in the glass network structure were observed and the presence of neo-formation products was determined

High-pressure Raman spectroscopy of Ca(Mg,Co)Si2O6 and Ca(Mg,Co)Ge2O6 clinopyroxenes

In situ high-pressure Raman spectra were collected on four pyroxenes, with composition CaCoSi2O6, CaMgSi2O6, CaCoGe2O6 and CaMgGe2O6, up to P = 7.6 and 8.3 GPa for silicates and germanates, respectively. The peak wavenumbers \ucf\u85i increase almost linearly with pressure; the slope d\ucf\u85i/dP is more pronounced for the modes at higher wavenumbers, and higher in germanates than in silicates. No phase transition or change in the compressional behaviour was observed within the investigated P-range. The strong dependence of the peak position with pressure of the high energy stretching modes is due to the high sensitivity of the vibrational frequencies probed by Raman spectroscopy to subtle changes in the tetrahedral deformation, which are overlooked by single-crystal X-ray diffraction