Raman analysis on 18th century painted wooden statues

A micro-Raman investigation on four wooden polychrome sculptures of Jan Geernaert (1704-1777), a Flemish sculptor who worked in Italy in the 18th century, is presented. The statues, representing the Holy Virgin Mary, with the infant Jesus in three of them, were created in the period 1750-1770 and are all made by poplar wood. The purpose of the micro-Raman investigations was to identify the original pigments used in 18th century, after later repainting interventions. In all statues, wood is covered by a groundwork, made by gypsum and animal glue. All pigments were identified, both in the original pictorial cover or in later repainted layers. Pigments were spread on a white lead layer (the so called imprimitura). Attention was particularly focused on the blue colours of the Holy Virgin mantle. In the external repainted layers, Prussian blue (Iron(II,III) hexacyanoferrate(II,III)) was found, together with ultramarine blue, a synthetic pigment, alternative to natural precious lapis lazuli, accessible on or after 1828. In one case, phthalocyanine blue is found, confirming a recent (later than 1930-35) restoration. The original skin colours are obtained by white lead and cinnabar (HgS), while the repainted layers are made by mixing chrome yellow (PbCrO4, synthesized in 1809), zinc yellow (ZnCrO4, 1809), red lead (Pb3O4), ultramarine blue, cinnabar, hematite (Fe2O3), goethite (-FeOOH), calcite (CaCO3) and white lead

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.

Prefronto-cerebellar transcranial direct current stimulation increases amplituded and decreases latency of P3b component in patients with euthymic bipolar disorder

INTRODUCTION: Neurocognitive impairments have been observed in patients with bipolar disorder (BD) even during the euthymic phase of the disease, potentially representing trait-associated rather than state-associated characteristics of the disorder. In the present study, we used transcranial direct current stimulation (tDCS) applied to cerebellar and prefrontal cortices to improve the neurophysiological performances of patients with euthymic BD. METHODS: Twenty-five outpatients with BD underwent open-label prefrontocerebellar tDCS for 3 consecutive weeks. Neurophysiological performances were assessed through the examination of the P3b and P3a subcomponents of P300 event-related potential at baseline and after stimulation. RESULTS: Compared to baseline, P3b component after tDCS showed significantly higher amplitude and shorter latency (latency: Fz P=0.02, Cz P=0.03, and Pz P=0.04; amplitude: Fz P=0.24, Cz P=0.02, and Pz P=0.35). CONCLUSION: In our sample of patients with euthymic BD, concomitant prefrontoexcitatory and cerebellar-inhibitory modulations led to improved brain information processing stream. This improvement may at least partially result from neuroplastic modulation of prefrontocerebellar circuitry activity

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

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