1,720,963 research outputs found
Real-time fluorescence imaging of a heterogeneously catalysed Suzuki?Miyaura reaction
No full textThe palladium-catalysed Suzuki-Miyaura reaction is one of the most important methods for C-C cross-coupling, yet the heterogeneous version of this reaction remains poorly understood. More specifically, the question of whether the reaction occurs on the surface of the catalyst (heterogeneous process) or is promoted by leaching of palladium species in solution (homogeneous phase) is still under debate. Here, we use real-time high spatial resolution microscopy to monitor a palladium-catalysed coupling reaction that produces a highly fluorescent BODIPY dye. We show catalyst migration during the reaction, which we attribute to a dissolution/redeposition mechanism where migrating palladium species become true active sites after attachment to the catalyst support. The observed process is heterogeneous, but the active catalysts (atoms or small clusters) have important mobility, as revealed by the observation of migrating catalytic sites. Our report shows the strength of single-molecule studies for unveiling fundamental mechanisms in heterogeneously catalysed reactions that are otherwise difficult to explore with classical ensemble experiments.There has been a long-standing debate on whether heterogeneously catalysed Suzuki cross-couplings can occur homogeneously due to metal leaching. Here the authors show that while the palladium from the nanoparticle catalyst is mobile during the reaction, the active sites remain heterogeneous in nature
Label-free multiphoton microscopy: Much more than fancy images
Full text linkMultiphoton microscopy has recently passed the milestone of its first 30 years of activity in biomedical research. The growing interest around this approach has led to a variety of applications from basic research to clinical practice. Moreover, this technique offers the advantage of label-free multiphoton imaging to analyze samples without staining processes and the need for a dedicated system. Here, we review the state of the art of label-free techniques; then, we focus on two-photon autofluorescence as well as second and third harmonic generation, describing physical and technical characteristics. We summarize some successful applications to a plethora of biomedical research fields and samples, underlying the versatility of this technique. A paragraph is dedicated to an overview of sample preparation, which is a crucial step in every microscopy experiment. Afterwards, we provide a detailed review analysis of the main quantitative methods to extract important information and parameters from acquired images using second harmonic generation. Lastly, we discuss advantages, limitations, and future perspectives in label-free multiphoton microscopy
A Prevention through Design Approach for the Environmental S&H Conditions and the Ventilation System at an Italian Underground Quarry
Full text linkEven if the number of the Italian underground quarrying operations is steadily growing, in many cases the safety criticalities are somehow underestimated, in spite of the regulations D.Lgs. 81/08 and D.Lgs. 624/96, Italian enforcements of the former European Directives 89/391/EEC, 92/91/EEC and 92/104/EEC. Ventilation system is conceived to face very simplified requirements, whilst critical pollutants or emergency situations are not taken in due consideration. Asides, the ventilation system fault and availability analysis are seldom included in the project. The paper deals with the results of a research work started some years ago at an underground quarry exploited through drift sublevel based on drill and blast technique, to identify criteria suitable to grant effective safety and health -S&H- conditions for the workers operating in the underground in the Prevention through Design approach. Taken into account that the phases for an effective approach to the S&H problems in underground must follow a hierarchic method, in which the risk management should be faced from an effective hazard reduction to a minimum at the sources, and the ventilation should be considered only as a 4th level solution, the possibilities of control at the main pollution sources, i.e. the emission of pollutants due to the rock winning and mucking operations, have been examined. The residual risk was then faced with both the original underground and airways layout definition for a new exploitation development, based on technical and efficiency considerations, and on fire emergency computer simulations. Finally, the paper summarizes the results of an availability analysis of the ventilation system for normal operating conditions, and the emergencies management, on the basis of the results of Hazard Evaluation techniques, particularly Hazard and Operability Analysis and Fault Tree Analysis
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
Variations 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
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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