When Red Turns Black: Influence of the 79 AD Volcanic Eruption and Burial Environment on the Blackening/Darkening of Pompeian Cinnabar.

It is widely known that the vivid hue of red cinnabar can darken or turn black. Many authors have studied this transformation, but only a few in the context of the archeological site of Pompeii. In this work, the co-occurrence of different degradation patterns associated with Pompeian cinnabar-containing fresco paintings (alone or in combination with red/yellow ocher pigments) exposed to different types of environments (pre- and post-79 AD atmosphere) is reported. Results obtained from the in situ and laboratory multianalytical methodology revealed the existence of diverse transformation products in the Pompeian cinnabar, consistent with the impact of the environment. The effect of hydrogen sulfide and sulfur dioxide emitted during the 79 AD eruption on the cinnabar transformation was also evaluated by comparing the experimental evidence found on paintings exposed and not exposed to the post-79 AD atmosphere. Our results highlight that not all the darkened areas on the Pompeian cinnabar paintings are related to the transformation of the pigment itself, as clear evidence of darkening associated with the presence of manganese and iron oxide formation (rock varnish) on fragments buried before the 79 AD eruption has also been found.

Long-term in situ non-invasive spectroscopic monitoring of weathering processes in open-air prehistoric rock art sites.

In this work, an innovative non-destructive monitoring methodology based on the analysis over time of open-air rock art sites is presented. This approach is based on the combination of in situ spectroscopic and chemometric studies to diagnose and monitor the state of conservation of rock art sites. Data acquired over a period of time by non-invasive analytical techniques such as portable Raman spectrometry (RS) and handheld energy-dispersive X-ray fluorescence (HH-EDXRF) spectrometry are compared to detect physicochemical changes that could affect the rock painting integrity. To demonstrate the applicability of the proposed procedure, three analysis campaigns (between 2013 and 2016) were carried out, analyzing Levantine rock pictographs preserved in the rock shelter of Solana de las Covachas VI (Albacete, Spain; see Electronic Supplementary Material (ESM) Fig. S1). The analyzed areas showed different types of active weathering processes such as gypsum and calcium oxalate formation, giving rise to conservation issues such as painting fading, surface loss, microbial colonizations, and formation of crusts. Results evidence that the proposed methodology can be very useful to monitor chemical changes in the surface of the walls where the rock art is located, thus obtaining crucial information for its preservation and management.

Evaluation of black crust formation and soiling process on historical buildings from the Bilbao metropolitan area (north of Spain) using SEM-EDS and Raman microscopy.

In the present work, several building materials suffering from black crusts and soiled surfaces were evaluated by scanning electron microscopy energy dispersive X-ray spectrometry (SEM-EDS) and micro-Raman spectroscopy. The goal was to examine the elemental and molecular composition, the distribution on the samples, and the morphology of endogenous and exogenous compounds on those black crusts and soiled surfaces. The black crusts were deposited over different building materials such as limestone, sandstone, and brick that constitute a small construction called "malacate" as well as over a limestone substrate of a cemetery gate. Both constructions are dated back to the beginning of the twentieth century. The samples of soiling were taken from the façade of a building constructed in the 1980s. The analytical evaluation allowed in a first stage the determination of the composition and the observation of the morphology of soiling and black crusts. In addition, the evaluation of the compositions of the soiling and black crusts of different grade and formation allowed the assessment of the main weathering phenomena that the buildings have suffered, which were found to be sulfate impact, marine aerosol impact, depositions of metallic particles, crustal particulate matter depositions, carbonaceous particles, biodeterioration, and vandalism.

Retinal cell imaging in myopic chickens using adaptive optics multiphoton microscopy.

Abnormal eye growth induced by visual deprivation can modify the structure and density of the retinal cells. We have used an adaptive optics multiphoton microscope to image photoreceptors (PRs) and ganglion cells (GCs) at different retinal locations in unstained retinas of chicken eyes with about 10D of myopia and their normal-sighted fellow eyes. In all samples, the local averaged inter-PR distance increased with eccentricity. No significant differences in PR density were found between control and myopic eyes. GC density declined in myopic eyes compared to control eyes and the inter-cell distance increased. In normal eyes, the size of the GC cell bodies increased approximately two-fold between the area centralis and the peripheral retina. In myopic eyes, this trend was preserved but the GC bodies were larger at each retinal location, compared to control eyes. Obviously, GC morphology is changing when the retinal area is enlarged in myopic eyes.

Tailor-made three-dimensional hybrid scaffolds for cell cultures.

The construction of the ideal three-dimensional scaffold for cell culture is one of the most intriguing topics in tissue engineering. It has been shown that cells can be cultured on most organic biomimetic materials, which now are losing popularity in favour of novel, hybrid systems. In this study, a series of photosensitive sol-gel hybrid materials, based on silicon-zirconium and silicon-titanium oxides, have been investigated for their suitability in three-dimensional scaffold fabrication. These materials can be structured by two-photon polymerization, a laser-based technique allowing the fabrication of micrometre-size structures with submicron resolution. The work presented here examined the effect of the organic/inorganic composition of the materials on cell behaviour and the establishment of a 'cell-culture friendly' environment. This is vital for cell adhesion, growth and differentiation, as the organic part of the material provides the soft matrix for cell growth, whereas the inorganic component gives the mechanical stability and rigidity of the three-dimensional structures. In addition, the use of femtosecond laser structuring permits the fabrication of a wide range of mechanically stable scaffolds of different sizes and shapes to be tested in terms of cell viability, proliferation and orientation.

Analysis of the chicken retina with an adaptive optics multiphoton microscope.

The structure and organization of the chicken retina has been investigated with an adaptive optics multiphoton imaging microscope in a backward configuration. Non-stained flat-mounted retinal tissues were imaged at different depths, from the retinal nerve fiber layer to the outer segment, by detecting the intrinsic nonlinear fluorescent signal. From the stacks of images corresponding to the different retinal layers, volume renderings of the entire retina were reconstructed. The density of photoreceptors and ganglion cells layer were directly estimated from the images as a function of the retinal eccentricity. The maximum anatomical resolving power at different retinal eccentricities was also calculated. This technique could be used for a better characterization of retinal alterations during myopia development, and may be useful for visualization of retinal pathologies and intoxication during pharmacological studies.

Multiphoton microscopy of ex vivo corneas after collagen cross-linking.

PURPOSE: To investigate changes in the morphology of the corneal stroma after collagen cross-linking (CXL) treatment in bovine and porcine eyes using a nonlinear microscope providing both two-photon excitation fluorescence (TPEF) and second harmonic generation (SHG) corneal images. METHODS: Freshly enucleated eyes were imaged using a tomographic nonlinear imaging method that was highly suitable to track temporal changes in corneal structures. CXL (riboflavin instillation plus UV irradiation) was applied on the enucleated eyes using similar protocols as in the clinic. A set of eyes without treatment were measured to be used as control. RESULTS: In control corneas, SHG images showed a regular distribution of lamellae across the stroma that appeared stable for at least 6 hours postmortem. CXL changed the collagen distribution pattern showing some abnormal structures. TPEF revealed a large reduction in corneal thickness in CXL corneas immediately after treatment. The changes in the distribution of collagen bundles appeared also in corneas treated with riboflavin only, but not followed by UV irradiation. SHG tomography also revealed a partial recovery of the corneal thickness with time. CONCLUSIONS: Nonlinear microscopy (in both tomographic and regular XY imaging configurations) was used to study spatial and temporal changes in the cornea during and after CXL on intact ocular globes. SHG imaging showed changes in the morphology of anterior corneal stroma after CXL. Regular collagen patterns turned into random distributed structures with thicker bundles at some localized areas. This might be a consequence of the corneal thickness decrease as a result of riboflavin-dextran instillation.

Ultra-low shrinkage hybrid photosensitive material for two-photon polymerization microfabrication.

Investigations into the structuring by two-photon polymerization of a nonshrinking, photosensitive, zirconium sol-gel material are presented. This hybrid material can be photostructured even when it contains up to 30 mol % of zirconium propoxide (ZPO); by varying the material's inorganic content, it is possible to modify and tune its refractive index. The introduction of ZPO significantly increases the photosensitivity of the resulting photopolymer. The fabricated three-dimensional photonic crystal structures demonstrate high resolution and a clear band-stop in the near-IR region. In contrast to common practice, no additional effort is required to precompensate for shrinkage or to improve the structural stability of the fabricated photonic crystals; this, combined with the possibility of tuning this material's optical, mechanical, and chemical properties, makes it suitable for a variety of applications by two-photon polymerization manufacturing.

Laser-induced breakdown spectroscopy (LIBS) in archaeological science--applications and prospects.

Laser-induced breakdown spectroscopy (LIBS) has emerged in the past ten years as a promising technique for analysis and characterization of the composition of a broad variety of objects of cultural heritage including painted artworks, icons, polychromes, pottery, sculpture, and metal, glass, and stone artifacts. This article describes in brief the basic principles and technological aspects of LIBS, and reviews several test cases that demonstrate the applicability and prospects of LIBS in the field of archaeological science.

Developmentally regulated expression and functional role of alpha 7 integrin in the chick embryo.

Integrin alpha 7 beta 1 is a specific cellular receptor for laminin. In the present work, we studied the distribution pattern of the alpha 7 subunit by immunofluorescence and immunoprecipitation and the role of the integrin by blocking antibodies in early chick embryos. alpha 7 immunoreactivity was first detectable in the neural plate during neural furrow formation (stage HH5, early neurula, Hamburger & Hamilton 1951) and its expression was upregulated in the neural folds during primary neurulation. The alpha 7 expression domain spanned the entire neural tube by stage HH8 (4 somites), and was then downregulated and confined to the neuroepithelial cells in the germinal region near the lumen and the ventrolateral margins of the neural tube in embryos by the onset of stage HH17 (29 somites). Expression of alpha 7 in the neural tube was transient suggesting that alpha 7 functions during neural tube closure and axon guidance and may not be required for neuronal differentiation or for the maintenance of the differentiated cell types. alpha 7 immunoreactivity was strong in the newly formed epithelial somites, although this expression was restricted only to the myotome in the mature somites. The most intense alpha 7 immunoreactivity was detectable in the paired heart primordia and the endoderm apposing the heart primordia in embryos at stage HH8. In the developing heart, alpha 7 immunoreactivity was: (i) intense in the myocardium; (ii) milder in the endocardial cushions of the ventricle; (iii) intense in the sinus venosus; (iv) distinct in the associated blood vessels; and (v) undetectable in the dorsal mesocardium of embryos at stage HH17. Inhibition of function of alpha 7 by blocking antibodies showed that alpha 7 integrin-laminin signaling may play a critical role in tissue organization of the neural plate and neural tube closure, in tissue morphogenesis of the heart tube but not in the directional migration of pre-cardiac cells, and in somite epithelialization but not in segment formation in presomitic mesoderm. In embryos treated with alpha 7 antibody, the formation of median somites in place of a notochord was intriguing and suggested that alpha 7 integrin-laminin signaling may have played a role in segment re-specification in the mesoderm.