1,721,272 research outputs found
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
Quantitative MR T1 measurements with TOWERS: T-One with enhanced robustness and speed
Full text linkT1 mapping can be beneficial for many applications in magnetic resonance imaging. Such applications include sequence optimization, clinical utility and tissue segmentation. However, the methods in the T1 mapping literature proposed to date either take a great deal of time to acquire or suffer from fundamental shortcomings. In addition, if significant motion occurs even once early in the scan, the operator needs to rerun the sequence, which is costly and time-consuming. Therefore, it is desirable to design a sequence that is not only fast, but also reliable to yield a good-quality T1 map, even in the presence of motion. In this study, we propose an EPI-based sequence with an efficient slice reordering scheme introduced relatively recently. The proposed sequence acquires saturation recovery samples that not only help improve estimation accuracy, but also serve as references for estimating motion parameters that will be used for mitigating the effects of motion. Furthermore, the reconstruction parameters are updated in the middle and at the end of the scan, and are used to retrospectively correct for motion. Phantom and in vivo experiments show the promise of the method.Doctor of Philosoph
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
Single scan MR velocity quantification in ROI by alternating velocity encoding gradient pulse polarity between phase encoding steps
Full text linkA single scan phase contrast method for quantifying velocity in a region of interest (ROI) containing flowing spins identified prior to scanning is introduced. k-space coverage involves applying positive velocity encoding gradient pulses in acquiring odd phase encoding lines and negative velocity encoding gradient pulses in acquiring even phase encoding lines or vice versa, effectively under sampling flowing spins by a factor of two. A ghost image due to flowing spins in the ROI is formed. The ghost image is located half a field of view away from the ROI in the phase encoding direction. Prior to image acquisition, the field of view in the localizer image is adjusted so that the subsequent ghost image does not overlap with the object being imaged. Velocity quantification is done using image values in ROI and the ghost image. The proposed method is compared to conventional phase contrast in phantom and in vivo. The proposed method reduces scan time considerably
Effects of chronic hypertension and acute cerebral ischemia on blood-brain barrier permeability, brain water content, and cerebral blood volume using MRI
Full text linkThe process of stroke alters the vascular physiology of the brain. In this dissertation, we have focused on the assessment of cerebrovascular alterations under two ischemic conditions: chronic hypertension with increased cerebral blood perfusion pressure (CPP) and transient focal cerebral ischemia with decreased CPP via the stroke-prone spontaneous hypertensive rats (SHRsp) model and the suture model, respectively. Based on these two models, the temporal evolutions of water content, permeability of BBB and cerebral blood volume (CBV), were monitored using magnetic resonance imaging (MRI). In SHRsp rats, there was no significant water content increase before BBB breakdown, indicating the vasogenic nature of the edema. A weak linear relationship was found between the water content and the permeability to Gd-DTPA during edema development after BBB breakdown, suggesting that the movement of water into brain tissue could have been facilitated by the increase in cerebrovascular permeability to such small molecules as Gd-DTPA. In addition, our results showed that, in SHRsp rats, the occurrence of BBB breakdown was no later than the presence of hemorrhage and the decrease of CBV under the symptoms of weight loss and enlarged ventricles. In a suture model of 90 min occlusion, while BBB permeability followed a biphasic pattern, the water content showed an increasing trend. BBB leakage did not play an important role in water content increase out to at least 6hr after reperfusion. After that, BBB breakdown worsened the edema formation. When permeability was recovered at 24 hr after reperfusion, water content reached its maximal value of the study period. In conclusion, though both chronic hypertension with increased CPP or acute ischemia with decreased CPP can result in BBB breakdown and edema development, the stroke development patterns are different under these two conditions. Our results shed some light on the roles of BBB breakdown in edema formation, may help to evaluate and monitor the effectiveness of therapeutic intervention, and may aid the development of new therapies targeted at maintainance of the BBB
Towards Quantitative Assessment of Human Functional Brain Development in the First Years of Life
Full text linkCharacterizing the developmental process of human brain function is of critical importance not only in gaining insight into its maturing architecture but also in providing essential age-specific information for assessment and monitoring of both normal and abnormal neurodevelopment. The recent development of non-invasive neuroimaging techniques, particularly resting-state functional connectivity magnetic resonance imaging (rfcMRI) has opened a window into very early functional brain development. Together with diffusion tensor imaging (DTI), rfcMRI offers the unique opportunity to tackle a largely unknown area - early functional brain development as well as its structural underpinnings. In this dissertation, both rfcMRI and DTI were utilized to delineate early brain development. Structurally, we found that white matter fiber tracts experience most rapid axonal development as well as myelination in the first year, followed by a much slower but steady growth thereafter. Spatially, the central white matter tracts develop earlier than the peripheral ones. Functionally, by focusing on one of the most salient high-order cognitive networks during the resting condition (absence of any goal-directed tasks) - the default-mode network, our results showed early emergence of this network in neonates, followed by dramatic synchronization during the first year of life and an adult-like architecture in 2yr olds regarding the core regions. Moreover, we found the anti-correlation (competing functions) between the default network and the task positive network is largely mediated by the frontal-parietal control system using both regional and newly designed network-level approaches, shedding light on brain's functional interaction patterns at a network level. Finally, focusing on the whole brain architecture, our results showed interesting patterns of brain's functional organization development. Specifically, the brain's functional architecture develops from more anatomically sensible to more functionally sensible; for the functional hubs, they gradually shift from sensory-related cortices to higher-order cognitive function related cortices. In conclusion, by focusing on neural circuit development at regional, network as well as whole brain levels and coupling with structural elements, our results delineated interesting and important functional circuits growth patterns and may shed light on the potential principles guiding normal early brain functional development
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