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.

Communicating Unexpected and Violent Death: The Experiences of Police Officers and Health Care Professionals

BACKGROUND

The notification of unexpected and violent death represents a challenging experience for police officers and health workers. These professionals are exposed to very intense emotions during this task.

AIM

We aimed to investigate the degree of preparation, and the emotions and attitudes of police officers and health professionals while communicating such a death.

METHOD

An ad hoc online questionnaire was created and disseminated through Qualtrics software. The participants were recruited through the institutional channels of Police, the College of Physicians, the ONG De Leo Fund and the Department of General Psychology of the University of Padua. In this qualitative study, thematic content analysis was used to examine the responses.

RESULTS

A total of 155 individuals participated in the study (44 females, 111 males): 102 individuals were police officers, 23 were doctors and were 30 nurses. Five main themes were identified: (1) how the communication took place; (2) the experiences during the communication; (3) the difficulties encountered; (4) coping strategies, and (5) forms of support. Most communications were performed in person, and most represented an intense emotional experience for the notifiers. There is a generalised lack of specific preparation and training for this practice. The recipient's characteristics (culture of origin, language, age, health conditions, psychological vulnerability) may add to the difficulties of the notification process. Professionals unload their tension by practicing sport, relying on their hobbies or interacting socially. The presence of other colleagues during and after the death notification is usually able to alleviate the burden of the communication.

CONCLUSIONS

Communication modalities can have a profound impact on the recipients and intensify the trauma of the loss; however, they also have the possibility of mitigating it. The notification of a violent and unexpected death remains a difficult and challenging task for the notifier, which is potentially stressful and emotionally charged. The topic is of great relevance and more research should be promoted in this area.

Receiving Notification of Unexpected and Violent Death: A Qualitative Study of Italian Survivors

(1) Background: The loss of a significant person can be especially traumatic when death comes without warning and is due to causes such as suicide, murder and accidents. The way an individual is informed about the loss can affect the way of adapting to the loss and the quality of life of survivors. Communication modalities of the notifier may deeply influence the bereavement process. Aim: The present investigation aimed to explore the experience of those who received communication of such a type of death by a professional figure. (2) Method: Snowball sampling was used to recruit the participants to this qualitative study. Social networks, word of mouth and researchers' acquaintances were used, including clients of the NGO De Leo Fund. A total of 52 Italian people (eight males and forty four females, mean age = 49.44; SD = 14.23) who received notification of the death of a loved one by police officers or by health professionals participated in the study. Deaths involved cases of suicide, murder, road accident and mountain accident. (3) Results: The following four key themes were identified: (a) how the communication took place; (b) reactions; (c) support; and (d) coping strategies. Only 22 participants reported having received clear information about the dynamics of what happened; the rest of the sample obtained only poor or ambiguous information. The majority of participants sought or received informal support from family and friends immediately after notification; however, some participants experienced a total lack of support. The opportunity to see the body of the loved one for the last farewell, when denied, caused discomfort in recipients of the news. (4) Conclusions: Even the impactful notification of a traumatic death such as suicide or road accident can be mitigated by the appropriate behaviour and attitude of notifiers, who should always avoid providing generic or ambiguous information about what happened. The notification process should not end with the simple transmission of the communication, but should also look at the following phases by including referral to supportive networks or bereavement services, aimed at assisting individuals in the immediate aftermath but also in the long term.

Effect of heating/cooling dynamics in the hysteresis loop and tunable IR emissivity of VO2 thin films

We experimentally investigate the semiconductor-to-metal transition (SMT) in vanadium dioxide thin films using an infrared thermographic technique. During the semiconductor to metal phase change process, VO₂ optical properties dynamically change and infrared emission undergoes a hysteresis loop due to differences between heating and cooling stages. The shape of the hysteresis loop was accurately monitored under different dynamic heating/cooling rates. In order to quantify and understand the effects of different rates, we used a numerical modelling approach in which a VO₂ thin layer was modeled as metamaterial. The main experimental findings are interpreted assuming that both the rate of formation and shape of metallic inclusions are tuned with the heating/cooling rate. The structural transition from monoclinic to tetragonal phases is the main mechanism for controlling the global properties of the phase transition. However, our experimental results reveal that the dynamics of the heating/cooling process can become a useful parameter for further tuning options and lays out a macroscopic optical sensing scheme for the microscopic phase change dynamics of VO₂. Our study sheds light on phase-transition dynamics and their effect on the infrared emission spectra of VO₂ thin films, therefore enabling the heating/cooling rate to be an additional parameter to control infrared emission characteristics of thermal emitters. The hysteresis loop represents the phase coexistence region, thus being of fundamental importance for several applications, such as the operation of radiative thermal logic elements based on phase transition materials. For such applications, the phase transition region is shifted for heating and cooling processes. We also show that, depending on the way the phase change elements are heated, the temperature operation range will be slightly modified.

Communication: Optically induced decoupling of the smectic-A and nematic order parameters at the AN phase transition in phototropic liquid crystals

In the present work, by means of the photopyroelectric calorimetric investigations in liquid crystal/naphtopyran (NP) molecule mixtures, the effect of the photoisomerization of NP by UV light on the critical behavior of specific heat could be studied over the smectic-nematic phase transition. It is shown that the UV light irradiation of the sample can shift the critical exponent from a non-universal value typical of the non-irradiated mixture to one close to that of the 3D-XY universality class, predicted for such a transition. This witnesses the optically triggered reduction of the coupling between the smectic and nematic order parameters responsible for the deviation from the XY-like behavior. A tentative explanation is provided based on the weakening of the order parameter coupling caused by the NP molecules entering the smectic layers following the UV light illumination.

Sensitivity to Heavy-Metal Ions of Unfolded Fullerene Quantum Dots

A novel type of graphene-like quantum dots, synthesized by oxidation and cage-opening of C60 buckminsterfullerene, has been studied as a fluorescent and absorptive probe for heavy-metal ions. The lattice structure of such unfolded fullerene quantum dots (UFQDs) is distinct from that of graphene since it includes both carbon hexagons and pentagons. The basic optical properties, however, are similar to those of regular graphene oxide quantum dots. On the other hand, UFQDs behave quite differently in the presence of heavy-metal ions, in that multiple sensitivity to Cu2+, Pb2+ and As(III) was observed through comparable quenching of the fluorescent emission and different variations of the transmittance spectrum. By dynamic light scattering measurements and transmission electron microscope (TEM) images we confirmed, for the first time in metal sensing, that this response is due to multiple complexation and subsequent aggregation of UFQDs. Nonetheless, the explanation of the distinct behaviour of transmittance in the presence of As(III) and the formation of precipitate with Pb2+ require further studies. These differences, however, also make it possible to discriminate between the three metal ions in view of the implementation of a selective multiple sensor.

Simultaneous calorimetric and polarization microscopy investigations of light induced changes over phase transitions in a liquid crystal-napthopyran mixture

We have studied the specific heat and the thermal conductivity in a 4-(n-octyl)-4'-cyanobiphenyl liquid crystal (LC)-photochromic molecules mixture, before, during, and after the photo-activation of the dispersed photochromic molecules, over both the smectic A-nematic and the nematic-isotropic phase transitions. The evaluation of the specific heat has enabled the determination of the changes of the phase transition characteristics induced by the photochromic molecules photoisomerization, while that of the thermal conductivity could be used to monitor the modifications induced in the average LC molecular orientation. The polarization microscopy imaging of the sample texture constituted a valuable support for the interpretation of the obtained thermal conductivity results.

Trace gas analysis from glazes by means of a compact photothermal deflection spectroscopy apparatus

A portable photothermal deflection spectroscopy apparatus for accurate analysis of gas mixtures containing volatile organic substances is presented. The main technical aspects of the photothermal deflection cell, and of the gas sampling equipment are discussed in details. Finally, we present a straightforward industrial application of the apparatus concerning the qualitative and quantitative analysis of the gas emissions from thermal treatment of ceramic glazes.

Dual beam differential photopyroelectric setup for broadband thermal effusivity investigation of glass transitions in polymers

The behaviour of the thermal effusivity squared over the glass transition in polystyrene is measured over a considerable frequency range using a novel dual beam front detection photopyroelectric configuration, which ensures a very effective processing of the obtained signal. This has enabled the detection of the very small changes taking place in such a parameter, despite the non-favourable sensitivity conditions due to the large mismatch between the thermal effusivities of the pyroelectric transducer and of the sample. The effect of the thermal contact resistance between the sample and the pyroelectric detector is also considered and discussed.

Study of the smecticA-hexaticB phase transition in homeotropic single domain samples of 65OBC liquid crystal by photopyroelectric calorimetry

The smecticA-hexaticB phase transition was studied in a homeotropic single domain sample and in a non-aligned sample of n-hexyl-4'-n-pentyloxybiphenyl-4-carboxylate liquid crystal compound to probe the effect of different amount of defects on the phase transition. The specific heat, the thermal diffusivity and the enthalpy exchange were monitored over the transition and, at the same time, polarization microscopy observations could be carried out. The transition during the first cooling run was found to be accompanied by a considerably larger defect annealing in the non-aligned sample than in the homeotropic one, but the critical behaviour of the specific heat remained substantially the same.

Hidden Text Detection by Infrared Thermography / Anwendung der aktiven Infrarotthermographie (IRT) zur Erfassung von verdeckten Texten / Utilisation de la thermographie infrarouge (IRT) pour détecter des textes cachés

We present an opto-thermal approach based on the use of active infrared thermography (IRT) for the study of texts hidden inside the bookbinding structure of ancient books. In particular we focus our investigation on the detection and characterization of texts on paper scraps, belonging to earlier handwritten or printed leaves, used for the making of bookbindings and lying between the end papers and the cover. A qualitative description of the physical mechanisms allowing the identification of texts is proposed and a comparative analysis of the results obtained by means of different IRT experimental configurations is presented. The results show that active IRT can be a very useful tool for the detection and the identification of underlying texts whose reading can provide useful information on the specific history of ancient books.

Invited review article: Photopyroelectric calorimeter for the simultaneous thermal, optical, and structural characterization of samples over phase transitions

The study of thermophysical properties is of great importance in several scientific fields. Among them, the heat capacity, for example, is related to the microscopic structure of condensed matter and plays an important role in monitoring the changes in the energy content of a system. Calorimetric techniques are thus of fundamental importance for characterizing physical systems, particularly in the vicinity of phase transitions where energy fluctuations can play an important role. In this work, the ability of the Photopyroelctric calorimetry to study the versus temperature behaviour of the specific heat and of the other thermal parameters in the vicinity of phase transitions is outlined. The working principle, the theoretical basis, the experimental configurations, and the advantages of this technique, with respect to the more conventional ones, have been described and discussed in detail. The integrations in the calorimetric setup giving the possibility to perform, simultaneously with the calorimetric studies, complementary kind of characterizations of optical, structural, and electrical properties are also described. A review of the results obtained with this technique, in all its possible configurations, for the high temperature resolution studies of the thermal parameters over several kinds of phase transitions occurring in different systems is presented and discussed.

Simultaneous characterization of optical and thermal parameters of liquid-crystal nanocolloids with high-temperature resolution

We report on the high-temperature resolution measurements of the optical and thermal parameters of a liquid-crystal-silica nanoparticle colloid, as well as its video inspection, simultaneously performed in an upgraded photopyroelectric calorimeter. Over the nematic-isotropic coexistence region, the determined nematic correlation length, obtained from turbidity measurements, showed the characteristic two-step nematic nucleation process previously reported only for the specific heat.

Strain effects at the hexatic-B-smectic-A transition in the 65OBC liquid crystal

We have studied the hexatic-B-smectic-A (HexB-SmA) transition in n -hexyl- 4'-n -pentyloxybiphenyl-4-carboxylate (65OBC) by means of a high-resolution ac photopyroelectric (PPE) calorimetric technique. A procedure for the interpretation of the PPE data, which allows the detection of an internal heating source due to strain annealing and/or latent heat, has been applied. We have found that the strain present in the sample depends on the kinetics of formation of the smectic phase once the sample is cooled from the isotropic one. The strain field keeps memory of this kinetics and can be only partially annealed on decreasing the temperature or cycling it around the Hex-SmA transition. A reversible ordering-disordering process has been found at T(c) and has been explained in terms of the competition between the order parameter variation with temperature and the constraints imposed by the disorder. The results confirm that the transition has a weakly first-order character with a specific heat critical exponent that disagrees with the available theoretical predictions. Our data show the importance of the disorder in 65OBC and we tried to clarify what would be the consequence of this result in theoretical modeling devoted to solving the puzzle of the HexB-SmA transition in this compound.

Dynamics of nematic liquid crystal with quenched disorder in the random dilution and random field regimes

By means of specific heat spectroscopy, we have studied the dynamics of nematic 8CB nucleated, in the presence of random disorder, as the temperature is lowered across the isotropic to nematic phase transition such that the crossover region of random dilution to random field regimes of disorder strength is explored. We show, in terms of frequency dependence, hysteretic behavior, and aging effects, that the out-of-equilibrium properties of the nematic nucleated in the random disorder regime are strongly reminiscent of the bulk material while the one grown in the random field regime shows a glassy behavior with aging leading to slower dynamics. The aging effect has been explained in terms of strain relaxation in analogy with observations in other soft glassy colloidal systems.