1,721,021 research outputs found
Multiple quantum coherences experiment, simulations and applications
No full textMULTIPLE QUANTUM COHERENCES EXPERIMENT, SIMULATIONS AND APPLICATIONS
ARMAN SAINOVITCH KUSSAINOV
Dissertation under the direction of Professor Daniel F. Gochberg
This dissertation discuses the intermolecular Multilpe Quantum Coherence (iMQC) phenomenon in nuclear magnetic resonance (NMR). This effect originates from the coherent long range dipole-dipole interaction between spins. A short introduction to nuclear magnetic resonance and the CRAZED experiment (the primary method to observe and study iMQC) is given. We perform numerical simulations of the CRAZED experiment, including relaxation processes, instantaneous radio frequency pulses and gradients, as well as phase cycling, phantom positioning, and sample rotation. The signal dependence on the sample
orientation, applied gradient strength and direction, and the underlying sample structure length scale has been determined experimentally and by numerical simulations for two biological tissues: rat sciatic nerve and mice fibrotic liver. The results indicate that the CRAZED signal may provide a unique means for elucidating sample structures at the hundreds of micrometers distance scale
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
Multi-exponential T2 Myelin Water Imaging in Ex-Vivo Rodent Brain at 7T and 15.2T
No full textTo apply MWI techniques to excised, fixed rodent brains, multi-exponential T2 (MET2) data were acquired at high (7T) and ultra-high (15.2T) fields with and without tissue doping with Gadolinium to increase SNR efficiency. From relaxivity measurements, optimal scan parameters are found based on the minimal Cramér-Rao lower bounds (CRLB) of variance of myelin water fraction (MWF). Subsequently acquired MET2 data were analyzed to obtain myelin water fraction (MWF) maps with and without contrast agent at each field strength with various techniques, displaying the potential for MWI in rodent brain in the study of myelin content across whole brain
Development and Characterization of NMR and MRI Methods for Assessment of Tumor Oxygen Consumption
No full textA common feature of invasive cancers is that they have an upregulation of glucose metabolism and reduced oxygen utilization. The overall goal of this research was to develop a 17Oxygen MRI method to access this aberrant tumor metabolism using a T1ρ weighted pulse sequence on a Bruker NMR Spectrometer. An assessment of the reliability of this pulse sequence for quantifying the ratio of concentrations of H217O (necessary for measuring the metabolic rate in vivo) water in 4 pairs of phantoms was preformed. Specifically, we varied the pH and concentration of Gadopentetic acid (Gd-DTPA) (which modulated T1 and T2 profiles) in 4 different combinations to mimic conditions in the tumor microeviorment. We then used the signal decay data collected at a low and high spin lock power and inserted this data into an eqaution. This equation was then used to compute the ratio of concentration between an enriched and unenriched phantom in each of the 4 pairs.
The two -frequency method was able to quantify [H217O] successfully in the phantoms without Gd-DTPA using the fitted signal data but failed to yield the correct result for the raw data. Thus, to further evaluate these approaches we need employ studies at clinical field strengths. Nevertheless, our results suggest that the quantification of H217O is insensitive to pH but sensitive to changes in T1 and T2
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
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
- …
