1,721,070 research outputs found
Quantum dot nanoparticles: Properties, surface functionalization, and their applications in biosensoring and imaging
No full textColloidal semiconductor nanocrystals, also known as Quantum Dots (QDs), posses unique properties due to their nanometric size. They have broad absorption spectra and narrow emission bands that are related to the materials used and to their size. QDs represent a new class of fluorescent probes that are gradually substituting traditional organic dyes since they present many advantages compared to them, first of all improved photostability. Furthermore, since QDs have broad absorption spectra, it is possible to excite many QDs using just one wavelength.
Much progress has been made in the last years in the synthesis of QDs, which now can yield highly homogeneous and highly crystalline QDs. Many strategies are also available nowadays to make QDs water soluble and biocompatible, the most common being the ligand exchange and polymer coating. The surface passivation of the QDs to make them water soluble also allows for further functionalization. As an example, if biological ligands are attached to the outer shell of the nanocrystals, they can selectively recognize specific targets. This approach can be exploited for numerous applications, among them biosensoring and imaging. Biosensors are a class of probes developed for biomarkers detection on a real-time or continuous basis in a complex mixture. This easy to use and low cost technique perfectly combines with the optical properties of QD. For example, the high photostability of QDs can allow for continuous monitoring of a signal over time. Furthermore, simultaneous detection of several specific receptors can be also achieved if many QDs with different emission colors are combined into a single structure, effectively behaving as an optical barcode. Optical imaging, in particular fluorescence imaging, is an area where QDs are gaining increasing popularity. Near-infrared wavelengths are of key importance for biological analysis since in this region biological tissues absorb only weakly. Few traditional organic dyes are available for such spectral window and in addition they suffer from photobleaching. On the other hand, QDs can be tuned to the desired emission wavelength by adjusting their composition and size. QDs have been already extensively used for cell imaging in vitro; however, the full potential of QDs can be appreciated only when they are employed in in vivo imaging. The preparation of multicolor probes which are highly stable in biological buffers and can be followed over long periods of time can be achieved by exploiting
the QDs properties. Although just in its infancy, biosensoring and imaging by means of QDs has already proved to be of paramount importance in biomedicine and future developments in QDs synthesis and functionalization will probably yield nano-tools of priceless value for medical application, e.g. for the early detection of diseases, such as in cancer diagnosis. In this chapter, we will try to give to the reader a general overview on the many aspects of QDs, mainly of their physical properties that are relevant for biological applications and on the strategies followed to make them biocompatible. Then the main biological applications of QDs will be reviewed, their implementation in biosensoring and imaging, both in vitro and in vivo, including their exploitation in photodynamic therapy. Finally, we will give an overview on the toxicity issues and on the upcoming new generations of QDs that should solve those issues
Quantitative assessment of myocardial blood flow with SPECT
No full textThe quantitative assessment of myocardial blood flow (MBF) and coronary flow reserve (CFR) may be useful for the functional evaluation of coronary artery disease, allowing judgment of its severity, tracking of disease progression, and evaluation of the anti-ischemic efficacy of therapeutic strategies. Quantitative estimates of myocardial perfusion and CFR can be derived from single-photon emission computed tomography (SPECT) myocardial perfusion images by use of equipment, tracers, and techniques that are available in most nuclear cardiology laboratories. However, this method underestimates CFR, particularly at high flow rates. The recent introduction of cardiac-dedicated gamma cameras with solid-state detectors provides very fast perfusion imaging with improved resolution, allowing fast acquisition of serial dynamic images during the first pass of a flow agent. This new technology holds great promise for MBF and CFR quantification with dynamic SPECT. Future studies will clarify the effectiveness of dynamic SPECT flow imaging
Beyond ultrasound: advances in multimodality cardiac imaging
No full textThe rapid technological evolution accomplished in noninvasive cardiac imaging techniques over the past few decades has provided physicians with a large armamentarium for the evaluation of patients with known or suspected coronary heart disease. Noninvasive assessment of coronary artery calcium or noninvasive coronary angiography may be performed using computed tomography or magnetic resonance imaging. These techniques evaluate the presence of atherosclerosis rather than ischemia. Conversely, nuclear cardiology is the most widely used noninvasive approach for the assessment of myocardial perfusion and function. These techniques coupled with the development of dedicated image fusion software packages to merge data sets from different modalities have paved the way for hybrid imaging. This article provides a description of the available noninvasive imaging techniques in the assessment of coronary anatomy, myocardial perfusion, and cardiac function in patients with known or suspected coronary heart disease
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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