1,721,262 research outputs found
Comparative study of surface-enhanced Raman scattering (SERS)methodologies for the detection of organic colorants in cultural heritage investigations
No full textIn recent years, the introduction of surface-enhanced Raman spectroscopy (SERS) in the field of cultural heritage investigations has significantly improved the possibilities of successfully identifying organic colorants, a class of artists’ materials that has been widely used in textile dyeing, paintings and other polychrome works of art since antiquity. Over the years, a number of SERS methodologies have been developed by different research groups to be applied to the analysis of dyes, including many types of metal substrates as well as several procedures of sample pretreatment.
In the present work, a comparative study has been carried out to shed light on the main advantages and disadvantages of the most relevant SERS approaches recently introduced in art analysis, namely SERS on Ag nanoparticles produced by laser photoreduction of AgNO3 solutions [Cañamares et al., 2007] and SERS on Ag colloids synthesized by microwave-supported glucose reduction of silver sulfate in the presence of sodium citrate as a capping agent [Leona, 2009]. Experiments on citrate/glucose microwave nanoparticles were conducted both in association with an extractionless HF gas-solid hydrolysis procedure [Leona et al., 2006] and without any pretreatment [Brosseau et al., 2009]. The performances of such methodologies for the ultrasensitive detection of a number of colorants from different supports were evaluated. Results obtained from pure dyes were compared with those achieved on actual samples, i.e. fragments from dyed paper and textiles, as well as lakes and glazes from several works of art. Extraction in HF vapours followed by the deposition of Ag citrate/glucose microwave nanoparticles on top of the sample was found in most cases to be the easiest and most rapid way to obtain high quality spectra. Indeed, such approach allowed us to record well resolved and extremely reproducible SERS spectra with high enhancement factors in less than 10 minutes for the great majority of samples here examined, leading to achieve, for colorants on different supports, a reliable fingerprint within very short times of analysis
Dimensioni e determinanti della qualità della vita. Uno studio sulle differenze di genere
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DEVELOPMENT OF INNOVATIVE ANALYTICAL PROCEDURES FOR THE IDENTIFICATION OF ORGANIC COLORANTS OF INTEREST IN ART AND ARCHAEOLOGY
Full text linkOrganic colorants obtained from natural sources such as plants and insects have been widely used as textile dyes or lake pigments for paintings, sculptures and other kinds of polychrome works of art since ancient times until the second half of the 19th century, when the industrial production of synthetic dyes had begun.
Chemical investigation of such materials is of great interest to art historians, restorers and art conservators. In fact, the analysis of ancient dyes can be of help in revealing what kind of substances were available in particular periods and geographical areas, providing valuable data about the historical context of a work of art, the lifestyle and the technical knowledge reached by a certain population in a given historical age, shedding light on the possible interactions between different cultures as well as the trade routes and commercial transactions which may have allowed the usage of a particular colorant far from its geographical source. Moreover, discovering nature and origin of the coloring substances employed in the production of a work of art can provide precious information regarding its original color and appearance, thus offering new insights into the artist’s choices and original intention, the techniques used and the dates ante quem and post quem the art object was produced, possibly leading to the uncovering of falsifications and forgeries. Furthermore, scientific analysis applied to the study of art materials and, specifically, of pigments and dyes, may contribute to assess suitable conservation and restoration procedures to be applied to paint defects and degraded pigments in works of art of any kind; in fact, time, environmental conditions and several other circumstances unavoidably cause damage and deterioration to art objects and artifacts, which therefore require careful conservation to be safeguarded as important elements of our cultural heritage.
The identification of historical dyes is currently one of the most challenging tasks in the chemical investigation of art materials, for three main reasons. First of all, colorants in works of art and archaeological textiles are usually included in complex matrixes such as paint layers or cloth fibers, where they are present in mixture with other substances, such as binding media or mordants, and in very low concentrations due to their high tinting power. Besides, sampling of art objects is always limited to microscopic fragments, when at all allowed. An additional analytical challenge is posed by the remarkable susceptibility to deterioration of organic materials, which can undergo a number of chemical degradation processes leading to the formation of specimens with a different molecular structure in comparison to the primary organic dye.
Several instrumental techniques, of both chromatographic and spectroscopic type, have been employed for the detection of colorants over the years. In recent times, the great potential of SERS has been appreciated, as the adsorption of the analyte on nanosized metal surfaces, resulting in a significant enhancement of the Raman scattering intensity and strong fluorescence quenching, leads to obtaining a specific fingerprint for many organic substances, markedly reducing the amount of sample that would be otherwise required for analysis. However, on the other hand, SERS poses a whole set of challenges, as only a small number of molecules have been studied so far and the necessity of searchable databases of reference materials is still to be fulfilled; moreover, SERS is not a separation technique, and therefore it often suffers from spectral interferences due to the presence of impurities or matrix components.
In this context, the present doctoral thesis work aims to the improvement of pre-existing analytical methods as well as to the development of innovative procedures for the identification of organic dyes of artistic and archaeological interest, with special attention being devoted to SERS. The scientific results here reported are the fruit of a research activity carried out both at Università degli Studi di Milano and in the Department of Scientific Research of the Metropolitan Museum of Art (New York, USA).
First of all, an effective experimental protocol for SERS analyses on silver colloids aggregated by NaClO4 was optimized and a wide spectral database of historical natural colorants was thus assembled, containing among the others the spectra of several dyes never studied before. The SERS procedure developed, in association with complementary analytical investigations of different kind, was then successfully applied to the identification of a yellow dye in ancient wool threads from the Libyan Sahara and to the detection of several colorants in Kaitag textiles, a unique embroidered textile art form from Caucasus.
Work carried out at the Metropolitan Museum of Art comprises a comparative study of the most relevant SERS approaches recently introduced in art analysis: relative merits and drawbacks of HF hydrolysis and non-hydrolysis methodologies were evaluated, and a two-step procedure for the investigation of organic dyes in works of art was proposed. Results obtained from reference dyes were compared with those achieved on samples taken from a number of artworks and ancient objects, including masterpiece oil paintings, musical instruments, archaeological textiles and lake pigments. Watercolors from a historical Winsor & Newton handbook dating to 1887 were then characterized using SERS and ordinary Raman spectroscopies, and a database of original art materials was acquired, to be used for dating as well as in authentication and identification studies. Also, coupling of TLC and SERS was investigated and tested as a promising tool for the separation and identification of the main alkaloid constituents of Syrian rue dye. Finally, a comprehensive Raman study of monobromoindigo, component of the historical colorant Tyrian purple, was performed, together with a detailed assignment of the spectral lines observed by comparison with density functional theory (DFT) quantum mechanical calculations
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Provision of the broadband video conference service via the integration of the IN and B-ISDN paradigms
No full textthis paper deals with the integration between the Intelligent Network (IN) and the B-ISDN for the support of advanced multimedia services. The focus of the paper is the proposal of a new role of the IN that, in a closed interaction with the B-ISDN, furnishes control functionalities to handle complex service configuration. In order to assign such a role, we distinguish different domains of control into the IN architecture and we propose functional models suitable to IN to cooperate for a global service provisioning. Some different options for an IN/B-ISDN interaction are discussed; in particular, architectural issues on the distribution of the IN control logic between the Service Control Function and the Service Switching Function are assessed. Finally we consider an actual multimedia service, the Broadband Video Conference, supported with the proposed approach, and we present some performance aspects
Searchable databases for the identification of organic colorants using surface-enhanced Raman scattering (SERS) : critical evaluation and possible approaches
No full textOrganic colorants have been used for millennia as textile dyes and as pigments for paintings and other kinds of polychrome works of art. Even today, natural and synthetic organic dyes are of great interest in the forensic field as food colorants, ink components and textile dyes. As they are often present in art objects in minute amounts due to their high coloring power, their identification is really challenging.
High-performance liquid chromatography (HPLC) and UV-visible spectroscopy have been routinely employed to detect dyes, but they require sizable samples. During the last few years, a lot of research in this field has been carried out by surface-enhanced Raman scattering (SERS), which has proven to be an extremely effective technique because of its great sensitivity.
Although the development of several micro-invasive analytical procedures has recently expanded the applicability of SERS spectroscopy in the art conservation and forensic fields, the necessity of obtaining a reliable match between spectra from unknowns and reference materials in a fast and convenient way is still to be fulfilled. In this context, the availability of extensive spectral databases as well as the accessibility of library search methods designed to match a query spectrum to the closest library references would significantly increase the spectral recognition rate, making the entire identification process considerably easier.
In the present work, a number of pure colorants, extracts from plants and insects, fragments from dyed paper and textiles, as well as lakes and glazes from several works of art were characterized by FT-Raman, ordinary Raman and SERS spectroscopies in different experimental conditions, and the spectra thus obtained were then used to build a searchable library. Preliminary attempts to classify query spectra against the library clearly showed that the search process is strongly affected by spectral variations which are completely unrelated to the identification goal, such as the amount of fluorescence, the background shape and the signal resolution. Improved results were achieved by searching against a second library, in which all the spectra were subjected to baseline correction and selective exclusion of certain spectral regions. Multivariate analysis methods, such as principal component analysis, will be applied to the spectra acquired thus far and evaluated to further improve the classification process and provide an easy, fast and reliable way to identify unknown dyes
Surface-enhanced Raman spectroscopy (SERS) on silver colloids for the identification of ancient textile dyes
No full textVariations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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