Photopyroelectric Investigation of the trans–cis Isomerization Effect on the Nematic- Isotropic Phase Transition of a Liquid Crystalline Azobenzene

Photopyroelectric calorimetry has been applied to the study of the effects of different concentration of photo-induced cis isomeric molecules on the characteristics of the nematic – isotropic phase transition in p,p’-diheptylazobenzene (7AB) samples. The investigations could be carried out by monitoring the behavior of the thermal diffusivity over the phase transition before and during the sample irradiation with UV light of varying intensity. Among other, it is shown that the monitoring of the time dependence of the thermal diffusivity at fixed sample temperature enabled the comparative study of the dynamics of the trans–cis and cis–trans isomeric transitions. It was shown that the increasing cis isomers concentration caused an increase in the fraction of material undergoing the phase transitions and increased the cis–trans conversion rate. Finally, polarization microscopy observations of the sample texture, which could be carried out together with the calorimetric evaluations proved useful for a more comprehensive analysis of the obtained results

Selectively Tunable Luminescence of Perovskite Nanocrystals Embedded in Polymer Matrix Allows Direct Laser Patterning

Cesium lead halide perovskite nanocrystals (NCs) have gained enormous attention as promising light-emitting and light-converting materials. Most of their applications require embedding NCs in various matrices, which is a challenging task due to their low stability, especially in the case of red-emitting CsPbI3 NCs. In this work, a new approach is proposed allowing the formation of red-emitting perovskite NCs by anion exchange induced directly inside a solid polymer matrix using green-emitting CsPbBr3 NCs as templates and iodododecane as an iodine source. Moreover, a simple and efficient route to photo-assisted termination of the anion exchange reaction in the polymer composite after reaching desired optical properties is demonstrated. The findings allow the authors to pattern a thin composite film with an ultrashort UV laser resulting in a selective generation of green- and red-emitting features with a 15 µm resolution

Thermographic Imaging in Cultural Heritage: A Short Review

Over the recent period, there has been an increasing interest in the use of pulsed infrared thermography (PT) for the non-destructive evaluation of Cultural Heritage (CH). Unlike other techniques that are commonly employed in the same field, PT enables the depth-resolved detection of different kinds of subsurface features, thus providing helpful information for both scholars and restorers. Due to this reason, several research activities are currently underway to further improve the PT effectiveness. In this manuscript, the specific use of PT for the analysis of three different types of CH, namely documentary materials, panel paintings–marquetery, and mosaics, will be reviewed. In the latter case, i.e., mosaics, passive thermography combined with ground penetrating radar (GPR) and digital microscopy (DM) have also been deepened, considering their suitability in the open field. Such items have been selected because they are characterized by quite distinct physical and structural properties and, therefore, different PT (and, in some cases, verification) approaches have been employed for their investigations

Thermographic and reflectographic imaging investigations on Baroque paintings preserved at the Chigi Palace in Ariccia

In this work, two different mid-infrared imaging techniques operating in the 3-5 μm spectral range are applied to the study of three paintings on canvas, dating back to the XVII century, preserved at the Chigi Palace in Ariccia (Italy). A combined approach based on the use of pulsed thermography and mid-infrared reflectography is proposed for the analysis of the 'Primavera' by Filippo Lauri and Mario Nuzzi, the 'Ritratto di Mario Nuzzi che dipinge un vaso di fiori' by Giovanni Maria Morandi and Mario Nuzzi and the 'Ebbrezza di Noee' by Andrea Sacchi. The aim is to show how the integrated use of these techniques enables a depth-resolved investigation of the entire layered structure of the paintings, from the surface up to the canvas support. The complementarity of the presented results allows an evaluation of the conservative status of the support and the detection of graphical and pictorial features hidden beneath the surface layer, such as pentimenti, as these features are important for the historical and artistic characterisation of the artefact

Two-Center Black Holes Duality-Invariants for stu Model and its lower-rank Descendants

We classify 2-center extremal black hole charge configurations through duality-invariant homogeneous polynomials, which are the generalization of the unique invariant quartic polynomial for single-center black holes based on homogeneous symmetric cubic special Kaehler geometries. A crucial role is played by an horizontal SL(p,R) symmetry group, which classifies invariants for p-center black holes. For p = 2, a (spin 2) quintet of quartic invariants emerge. We provide the minimal set of independent invariants for the rank-3 N = 2, d = 4 stu model, and for its lower-rank descendants, namely the rank-2 st^2 and rank-1 t^3 models; these models respectively exhibit seven, six and five independent invariants. We also derive the polynomial relations among these and other duality invariants. In particular, the symplectic product of two charge vectors is not independent from the quartic quintet in the t^3 model, but rather it satisfies a degree-16 relation, corresponding to a quartic equation for the square of the symplectic product itself.Comment: 1+31 pages; v2: amendments in Sec. 9, App. C added, other minor refinements, Refs. added; v3: Ref. added, typos fixed. To appear on J.Math.Phy

Structure and stability of traversable thin-shell wormholes in Palatini f(R)f(\mathcal{R}) gravity

We study the structure and stability of traversable wormholes built as (spherically symmetric) thin shells in the context of Palatini $f(\mathcal{R})$ gravity. Using a suitable junction formalism for these theories we find that the effective number of degrees of freedom on the shell is reduced to a single one, which fixes the equation of state to be that of massless stress-energy fields, contrary to the general relativistic and metric $f(R)$ cases. Another major difference is that the surface energy density threading the thin-shell, needed in order to sustain the wormhole, can take any sign, and may even vanish, depending on the desired features of the corresponding solutions. We illustrate our results by constructing thin-shell wormholes by surgically grafting Schwarzschild space-times, and show that these configurations are always linearly unstable. However, surgically joined Reissner-Nordstr\"om space-times allow for linearly stable, traversable thin-shell wormholes supported by a positive energy density provided that the (squared) mass-to-charge ratio, given by $y=Q^2/M^2$, satisfies the constraint $1<y<9/8$ (corresponding to overcharged Reissner-Nordstr\"om configurations having a photon sphere) and lies in a region bounded by specific curves defined in terms of the (dimensionless) radius of the shell $x_0=R/M$.Comment: 10 pages, revtex4-1 style. v2: some minor corrections, version accepted for publication in Phys. Rev.

Effect of X-ray and artificial aging on parchment

In this study, the employment of the X-ray irradiation as bioremediation method to treat parchment has been deeply investigated. In particular, the effect of the irradiation doses on the structural stability of collagen, the main constituent of parchment, has been evaluated on a series of modern parchment samples by means of different opto-thermal and spectroscopic techniques in order to obtain the dose-dependent effect of irradiation on collagen. Moreover, the long-term behavior of the irradiated parchment has been considered by analyzing the same series of samples after being hygrothermally artificially aged. Characterizations by light transmission analysis, Fourier transform infrared spectroscopy and the ultraviolet-visible-near infrared (UV-Vis-NIR) reflectance one have been performed for the identification of the radio-induced effect on the parchment structure even in a dose range much wider than the need for sterilization. The obtained results have proved the safeness of the method in the short and long term confirming the applicability of this emerging procedure

Evaluation of the irradiation treatment effects on ancient parchment samples

In this work, the effect of X-ray irradiation as a disinfection treatment in original ancient parchment samples, belonging to a discarded book cover of a 16th-century archival register, has been evaluated. Specifically, the bacterial and fungal species isolated from the book cover have been characterized and then irradiated with increasing doses of X-rays with the aim to evaluate the effectiveness of the antimicrobial protocol on the isolated microorganisms. The deterioration effects induced by the X-ray treatment as well as the natural aging on the collagen matrix of the parchment sample have been tested by employing several techniques, namely, Light Transmission Analysis, Fiber Optic Reflectance Spectroscopy, Attenuated Total Reflectance-Fourier Transformed Infrared spectroscopy, UV Resonant Raman spectroscopy and Atomic Force Microscopy. The results reveal that the irradiation treatment applied to our ancient parchment samples deteriorated by biological attack and other naturally occurring phenomena, possibly associated with inappropriate conservation conditions, does not seem to induce further damage factors even when large doses of irradiation are employed. The X-rays-based disinfection treatment effects are limited on the collagen support and this confirms the potential of this method in mass disinfection of library and archival materials

Remote and contactless infrared imaging techniques for stratigraphical investigations in paintings on canvas

AbstractIn the analysis of complex stratigraphical structures like painted artefact, infrared (IR) techniques can provide precious information about elements hidden under superficial layers of the artwork, such as pictorial features and structural defects. This paper presents a novel complementary use of reflectographic and thermographic techniques for the survey of three baroque paintings, preserved at the Chigi Palace in Ariccia (Italy). First, the IR-ITR laser scanner prototype has been used for the preliminary and remote near-IR reflectographic survey of the areas where the canvas was located. The resulting map was then used for planning the thermographic and mid-IR reflectographic studies, focusing the analyses on the most interesting areas of one of the paintings, called "La Primavera". The combination of the three imaging techniques revealed several details not visible by the naked eye, such as restored lacunas and pentimenti, demonstrating the validity and complementarity of the proposed combined methodologies

Tailoring surface properties, biocompatibility and corrosion behavior of stainless steel by laser induced periodic surface treatment towards developing biomimetic stents

Laser-Induced Periodic Surface Structures (LIPSS) holds great potential for regenerative biomedicine. Creating highly precise LIPSS enables to generate biomimetic implant surfaces with improved properties. The present study focuses on the fabrication and investigation of laser-treated stainless steel samples with applied linear LIPSS patterns with grooves made by means of a picosecond laser system using wavelengths of 1064 nm and 532 nm. To investigate properties of the laser-treated surfaces and to understand the basics of cell-surface interactions between the LIPSS and human Umbilical Cord Mesenchymal Stem Cells (UCMSC), flat stainless steel samples with various applied nanopatterns were used. Such LIPSSs demonstrated higher surface roughness, good biocompatibility, lower wettability and higher corrosion resistance compared to the untreated (polished) spec-imens. The surface roughness of laser-treated samples was in microscale that enabled adhesion and migration of endothelial cells, thus increasing the likelihood for endothelialisation. This thereby could reduce the chances for the development of Late Stent Thrombosis (LST) and In-Stent Restenosis (ISR). Furthermore, laser textured surfaces demonstrated an environment supportive for cell attachment, proliferation and alignment with the nanogroves. Therefore, application of the biomimetic nanopatterns could help to overcome frequent post-surgery complications after the stent implantation