1,720,984 research outputs found
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Evaluation of the Light Emission Kinetics in Luciferin/Luciferase-Based In Vivo Bioluminescence Imaging for Guidance in the Development of Small Animal Imaging Study Design
Get PDFBioluminescence imaging (BLI) is gaining acceptance as a small animal imaging modality useful for visualizing cellular and molecular activity in vivo, and especially for evaluating tumor development and efficacies of treatments. Various studies have validated the technique for a number of purposes, including the quantification of tumor burden; however, many basic questions have not been investigated whose answers may ultimately impact the conclusions drawn from the results. Primarily, consideration of the impact of BLI emission kinetics has not been rigorously addressed. This study provides information on the effects of different routes of luciferin substrate injection on the BLI kinetic profile, including time to peak emission, magnitude of peak emission, and emission decay characteristics. This study also presents for the first time the use of subcutaneous (s.c.) luciferin injection and the use of s.c. luciferin injection followed by continuous s.c. infusion (s.c.i.) for establishment of stable BLI light emission. Further, results are presented of the kinetic profile changes associated with 1) inhaled and injected anesthesia; and 2) ambient air heating on mouse core temperature. The study demonstrated substantial differences in the peak light emission with i.v. providing the highest, with s.c., s.c.i. and i.p yielding 30% or less of the light emission of the i.v. route. The correlations between tumor burden and BLI light emission were moderately strong (R>0.75) for each administration route, but at varying times following injection, providing information for establishment of optimal image start times. Surprisingly, ambient cooling of the animal while under anesthesia yielded peak light emissions of up to 100% higher than those obtained when ambient air heating was used to maintain mouse core temperature. Finally, guidelines are presented to aid investigators in development of BLI study design to give due consideration to luciferin administration routes, anesthesia protocol, and animal temperature maintenance
Noninvasive Assessment of Tumor Hypoxia Using MRI in Clinical and Preclinical Tumor Models
No full textTumor oxygenation influences response to radiation and plays important roles in malignant progression, angiogenesis and metastasis. While methods are available to quantitatively map pO2 dynamics in preclinical studies, new techniques are needed to noninvasively characterize tumor hypoxia and response to interventions in patients. Blood Oxygen Level Dependent (BOLD) MRI based on T2* contrast induced by deoxyhemoglobin concentration [dHb] is sensitive to tumor vascular oxygenation and blood flow. Meanwhile TOLD (Tissue Oxygen Level Dependent) MRI is sensitive to tissue oxygenation based on the shortening of the tissue water T1 due to molecular oxygen [O2]. In this study, I investigate the utility of BOLD and TOLD to evaluate tumor hypoxia in response to breathing hyperoxic gas in rats and test the feasibility of such measurements in patients.
All MRI experiments were performed on either a 4.7T small animal Varian or a 3T clinical Philips scanner. Variation in BOLD and TOLD signal response observed in two syngeneic prostate tumor models: Dunning R3327-AT1 and -HI, with respect to oxygen and carbogen breathing were compared with quantitative change in pO2 measured using Fluorocarbon Relaxometry using Echo Planar Imaging for Dynamic Oxygen Mapping (FREDOM). In addition, BOLD and TOLD MRI measurements were used to predict radiation treatment outcome following a single dose of 30 Gy. BOLD MRI was also assessed in cervical cancer patients in response to breathing oxygen (15dm3/min). Two sequences were tested, multiple-shot EPI and multi echo gradient echo, to allow comparison.
Significant correlations were found between BOLD and TOLD MRI and quantitative pO2 measurements for both oxygen and carbogen breathing. However, both gases had similar effect on modulating tumor hypoxia with no significant difference observed. The AT1 tumors showed a correlation between tumor growth delay for the animals breathing O2 during radiation and pre-irradiation TOLD responses to oxygen challenge. Finally, BOLD MRI at 3T was feasible for examining the potentially valuable biomarker of oxygenation seen in cervical cancer. Further parameters such as vascular perfusion and permeability based on DCE, cellularity based on diffusion, and TOLD response to oxygen challenge may also be readily incorporated into a dynamic evaluation
Dynamic Magnetic Resonance Imaging for Tumor Prognosis
No full textBreast and prostate cancers are the most common non-smoking cancers among American women and men. Radiotherapy and chemotherapy in conjunction with surgery are the most common treatment protocols in the clinic. However, a lot of experimental and clinical studies have shown that tumor hypoxia and the microcirculation play a very important role in cancer progression and therapy. There is strong evidence that hypoxic cells are one of the major reasons for failure to control tumors with conventional radiotherapy and chemotherapy. Several approaches (hyperthermia and carbogen inhalation), which improve tumor oxygenation during radiotherapy and chemotherapy, have been used in clinical trials. There is increasing demand for tumor prognostic information in the clinical setting. So far, increasing clinical data have indicated that poorly oxygenated tumors have poor prognosis. To better understand the underlying tumor physiological mechanisms, it is very important to develop novel non-invasive approaches to accurately assess tumor microcirculation and oxygenation for further therapy planning. However, these parameters have been extremely difficult to assess in routine clinical practice and have therefore not been easily integrated in to general patient care. With development of MRI the non-invasive technique, BOLD (Blood Oxygenation Level Dependent) contrast MRI, has been widely used for neuroscience research to detect brain activations. Because deoxyhemoglobin (dHbO2) is paramagnetic and oxyhemoglobin (HbO2) is non-magnetic, the change of concentration of deoxyhemoglobin and oxyhemoglobin can cause a Bulk Magnetic Susceptibility (BMS) change and the T2* signal response during MR imaging. Here, I applied this technique to assess tumor physiological characteristics. In order to study the BOLD mechanism, I designed a phantom system and built it for in-vitro study. Since inhalation of oxygen could cause variation in the blood flow and oxygenation, and BOLD MRI is sensitive to both these factors, it becomes very important to explore the correlation between the BOLD response and these two factors. Considering the different vascular orientation, the angle between vessel and the static magnetic field (B<sub.0) could be further analyzed in phantoms. The phantom study showed that contribution of oxygenation was much higher than that of flow to the BOLD signal. Interestingly, a signal decrease was observed in extra-vessel region accompany increasing intra-vessel oxygenation. The DCE (Dynamic Contrast Enhanced) and BOLD MRI have been compared in the animal experiments and the clinical setting. The experimental pre-clinical results showed that tumor sublines with different vascular development showed different DCE and BOLD regional response. This correlation between DCE and BOLD in regional response indicated the potential value of BOLD technique in tumor physiological research
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe 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
Tumor radio-sensitivity assessment by means of volume data and magnetic resonance indices measured on prostate tumor bearing rats
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