Retinal rods function as accurate photon counters to provide for vision under very dim light. To do so, rods must generate highly amplified, reproducible responses to single photons, yet outer segment architecture and randomness in the location of rhodopsin photoisomerization on the surface of an internal disk introduce variability to the rising phase of the photon response. Soon after a photoisomerization at a disk rim, depletion of cGMP near the plasma membrane closes ion channels and hyperpolarizes the rod. But with a photoisomerization in the center of a disk, local depletion of cGMP is distant from the channels in the plasma membrane. Thus, channel closure is delayed by the time required for the reduction of cGMP concentration to reach the plasma membrane. Moreover, the local fall in cGMP dissipates over a larger volume before affecting the channels, so response amplitude is reduced. This source of variability increases with disk radius. Using a fully space-resolved biophysical model of rod phototransduction, we quantified the variability attributable to randomness in the location of photoisomerization as a function of disk structure. In mouse rods that have small disks bearing a single incisure, this variability was negligible in the absence of the incisure. Variability was increased slightly by the incisure, but randomness in the shutoff of rhodopsin emerged as the main source of single photon response variability at all but the earliest times. Variability arising from randomness in the transverse location of photoisomerization increased in magnitude and persisted over a longer period in the photon response of large salamander rods. A symmetric arrangement of multiple incisures in the disks of salamander rods greatly reduced this variability during the rising phase, but the incisures had the opposite effect on variability arising from randomness in rhodopsin shutoff at later times.

Non-destructive portable techniques for the analysis of cultural heritage items are essential for enhancing our understanding of these objects and providing valuable information for potential restoration interventions. This paper presents a combined use of pulsed thermography, X-ray fluorescence, and Raman spectroscopy to investigate the ancient bronze “Il Togato”, yielding complementary information concerning the techniques used for creating this artefact and its conservation status. Specifically, thermographic analysis has highlighted the presence of many patches of different size used for emending superficial cast defects, weldings used to connect parts separately cast to the main structure, cracks, and defects located in the bronze thickness. On the other hand, XRF provided information on the composition of the gilding which characterises the statue, and supplied an estimate of its thickness through the use of a stratification model. Additionally, Raman spectroscopy has been applied to identify corrosion products. The experimental results presented in the paper provide a comprehensive knowledge of the bronze under investigation and assess the effectiveness of the portable non-destructive techniques employed in the analysis.

In the manufacture of ancient books, it was quite common to insert written scraps belonging to earlier library material into bookbindings. For scholars like codicologists and paleographers, it is extremely important to have the possibility of reading the text lying on such scraps without dismantling the book. In this regard, in this paper, we report on the detection of these texts by means of infrared (IR) pulsed thermography (PT), which, in recent years, has been specifically proven to be an effective tool for the investigation of Cultural Heritage. In particular, we present a quantitative analysis based, for the first time, on PT images obtained from books of historical relevance preserved at the Biblioteca Angelica in Rome. The analysis has been carried out by means of a theoretical model for the PT signal, which makes use of two image parameters, namely, the distortion and the contrast, related to the IR readability of the buried texts. As shown in this paper, the good agreement between the experimental data obtained in the historical books and the theoretical analysis proved that the capability of the adopted PT method could be fruitfully applied, in real case studies, to the detection of buried texts and to the quantitative characterization of the parameters affecting their thermal readability.

On the occasion of the 700th centenary of the death of Dante Alighieri, medium wave infrared imaging analysis of illuminations of the XIV-century code of the Divina Commedia (MS. 1102), hosted in the Biblioteca Angelica in Rome, was performed and discussed. The investigation was carried out by means of thermographic and reflectographic techniques on illuminations where the iconographic representation appeared severely damaged. In particular, through the combined use of both techniques, it was possible to recover the images of the damaged parts of the pictorial layer of the illuminations and of their underdrawings, displaying details of the “lost guardians”, which was useful to reconstruct the conservative history of the precious manuscript.

Pulsed thermography is a well-established method for the non-destructive analysis of cultural heritage items. This technique has been recently applied by the authors of this paper for reading written scraps, used for the making of bookbinding of ancient manuscripts, located between the end papers and the covers. The readability of the hidden text depends on several geometrical, optical and thermal parameters characterizing the typology of paper and the ink employed. To this end, a comprehensive mathematical model was developed by the authors for analyzing the influence of the various involved parameters. In particular, two indices were introduced, namely the signal contrast and the distortion index, used to quantitatively characterize the hidden text readability. Several numerical simulations are reported for assessing the dependence of the contrast and distortion from various parameters appearing in the model. Finally, a preliminary application to the analysis of original books is also presented.