1,721,048 research outputs found
Dynamics of liquids in confinement : application of Nuclear Magnetic Resonance Relaxometry
No full textPraca "Dynamika cieczy w ograniczonej geometrii - zastosowanie relaksometrii Magnetycznego Rezonansu Jądrowego" opisuje szczegółowo analizę i interpretację dyspersji szybkości relaksacji spin-sieć jonożeli opartych na dwóch cieczy jonowych: Tiocyjanianie 1-etylo-3-metyloimidazoliowym ([EMIM][SCN]) oraz l-butylo-3-metyloimidazoliowym siarczanie oktylu ([BMIM][0cS04]). Mianem jonożeli określa się układy, w których ciecz jonowa została unieruchomiona w stałych matrycach. Dzięki takiemu zabiegowi można je w bezpieczniejszy sposób wykorzystać jak o elektrolity w urządzeniach elektronicznych, bateriach itp. Z perspektywy potencjalnych zastosowań istotna jest jednak znajomość tego, jak fakt uwięzienia cieczy w ograniczeniu geometrycznym wpływa na dynamikę, a pośrednio na przewodnictwo jonowe finalnego produktu. W badaniach zastosowano metodę relaksometrii Magnetycznego Rezonansu Jądrowego (MRJ) typu FFC ("Fast Field Cycling") - tzw. szybkiego przemiatania pola. Technika ta jest unikalną metodą eksperymentalną umożliwiająca zidentyfikowanie mechanizmów i skali czasowej procesów dynamicznych zachodzących w układach molekularnych i jonowych, zarówno stałych, jak i ciekłych. Obserwacja relaksacji jądrowej 'H cieczy jonowych w warunkach swobodnych (czysta ciecz) i warunkach uwięzienia geometrycznego (ciecz umieszczona w matrycy krzemowej) wykazała zmiany dynamiki molekularnej w zależności od rodzaju cieczy jonowej i jej względnej zawartości w porach matrycy. Analiza profili dyspersji szybkości relaksacji spin-sieć 'H w szerokich zakresach częstości Larmora (4 kFlz - 40 MFIz) oraz dla szerokiego zakresu temperatur (223 - 253 K dla [EMIM][SCN] oraz 243 - 303 K dla [BMIMJIOCSO4]) pozwoliła na rozróżnienie i charakterystykę różnych mechanizmów dyfuzji jonów cieczy jonowych w szerokiej skali czasowej. Dogłębna analiza zależności dyspersyjnych szybkości relaksacji spin-sieć opierała się na dopasowaniu modelu zawierającego przyczynki do całkowitej relaksacji wynikające z fluktuacji oddziaływań dipol-dipol modulowanych przez dynamikę translacyjną i rotacyjną jonów. Dzięki różnej zależności funkcyjnej od częstotliwości Larmora, wkłady te można jednoznacznie rozdzielić i określić czasy korelacji charakteryzujące dany proces. Parametry opisujące procesy dyfuzji translacyjnej i rotacyjnej otrzymane dla cieczy w postaci swobodnej wykorzystano jak o punkt odniesienia do opisu zmienionej dynamiki jonów w warunkach ograniczenia geometrycznego. Wyróżniono dwie główne frakcje cieczy jonowej: znajdującą się w centrum poru, której dynamika była zbliżona do dynamiki czystej cieczy, oraz znajdującą się bliżej powierzchni matrycy krzemowej. Wyznaczono parametry charakteryzujące dynamikę: czasy korelacji oraz względne współczynniki dyfuzji, a ich zmienność z temperaturą opisano zależnością Vogel-Fulcher-Tammann. Jednym z istotniejszych wniosków pracy jest to, że pomimo oddziaływania z powierzchnią krzemową i efektów sterycznych dynamika translacyjna dla wszystkich badanych układów zachowuje trójwymiarowy charakter.The thesis "Dynamics of liquids in confinement - the application of Nuclear Magnetic Resonance Relaxometry" describes in detail the analysis and interpretation of the spin-lattice relaxation rate dispersion of ionogels based on two ionic liquids: l-ethyl-3-methyIimidazolium thiocyanate ([EMIM][SCN]) and I-butyl-3-methylimidazolium octyl sulphate ([BMIM][0 cS0 4 ]).The ionogel is a solid system within which the ionic liquid has been immobilized. Thanks to such solidification, they can be used in a safer way as electrolytes in electronic devices, batteries, etc. From the applicational point of view, it is important to know how the confinement affects the liquid dynamics and, indirectly, the ionic conductivity of the final product. The technique used for the research was Fast Field Cycling Nuclear Magnetic Resonance (FFC NMR) Relaxometry. This is a unique experimental method that allows to identify the mechanisms and time scale of dynamic processes in molecular and ionic systems, both solid and liquid. Observation of 1H nuclear relaxation of ionic liquids in free state (bulk liquid) and in confinement (liquid entrapped in silica matrices) revealed changes in molecular dynamics depending on the type of ionic liquid and its relative content within the pores of the matrix. Analysis of 1H NMR spinlattice relaxation rate dispersion profiles in broad Larmor frequency range (4 kHz - 40 MHz) and temperature range (223 - 253 K for [EMIM][SCN] and 243 - 303 K for [BMIM][0 cS0 4 ]) allowed to distinguish and characterize different mechanisms of ion diffusion taking place in different timescales. An in-depth analysis of the frequency dependence of spin-lattice relaxation rate was based on the model with the total relaxation rate decomposed into contributions that stem from the fluctuation of the dipole-dipole interactions modulated by the translational and rotational dynamics of the ions. Due to different functional dependence on the Larmor frequency, these contributions can be separated and the correlation times characterizing the given process can be determined. Parameters describing the translational and rotational diffusion processes obtained for liquids in a free form were used as a reference point to describe the dynamics of ions altered due to geometric confinement. Two main fractions of the ionic liquid were distinguished: first one located in the center of the pore, the dynamics of which was similar to the dynamics of the pure liquid, and the fraction of liquid closer to the surface of the silica matrix. Correlation times and relative diffusion coefficients have been determined, as well as their temperature dependence according to the Vogel-Fulcher-Tammann relationship. One of the most important conclusions of the work is that despite the interaction with the silica surface and the steric effects, the translational dynamics for all studied systems retains its three-dimensional character
Spektroskopia elektronowego rezonansu spinowego dla kompleksów metali przejściowych w roztworach i deutronowa spektroskopia rezonansu jądrowego : analogie opisu teoretycznego
No full textNMR Relaxometry Across Time: From Early Insights to Emerging Directions
Get PDFNuclear magnetic resonance (NMR) relaxometry has evolved from early theoretical insights into a dynamic and versatile analytical technique capable of probing molecular and ionic motion across diverse fields. Rooted in the foundational work by many different scientists (e.g., Bloch, Purcell, Torrey, Hahn, Bloembergen, Pound, and Solomon, just to name a few), relaxometry has progressed through pivotal advancements such as Redfield's theory and the development of time-domain (TD) and fast field-cycling (FFC) methodologies. While the former enables rapid, low-cost analysis of relaxation time distributions, widely applied in soft matter and quality control, the latter provides frequency-resolved nuclear magnetic resonance dispersion (NMRD) profiles that capture dynamic processes across multiple timescales, revealing deeper insights into molecular interactions in heterogeneous systems. Recent innovations in instrumentation have expanded the applicability of relaxometry. Moreover, its integration with modalities such as diffusimetry and imaging has opened new routes for spatially resolved and multimodal analyses. Applications now span materials science, biomedicine, and environmental studies. In polymers and porous media, relaxometry reveals segmental dynamics and surface interactions; in biological tissues, NMRD profiles differentiate healthy from pathological states, offering diagnostic potential. Emerging applications include contrast agent development, soil hydration analysis, microplastic detection, and wastewater monitoring. This paper offers a comprehensive overview of the field's historical trajectory, methodological advancements, and expanding application landscape. Emphasis is placed on the synergy between TD and FFC-NMR approaches and the ongoing transition toward portable, real-time, and multimodal relaxometric systems. NMR relaxometry is poised to become a mainstream tool in diagnostics, materials characterization, and environmental monitoring
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
R1 dispersion contrast at high field with fast field-cycling MRI
No full textContrast agents with a strong R1dispersion have been shown to be effective in generating target-specific contrast in MRI. The utilization of this R1field dependence requires the adaptation of an MRI scanner for fast field-cycling (FFC). Here, we present the first implementation and validation of FFC-MRI at a clinical field strength of 3 T. A field-cycling range of ±100 mT around the nominal B0field was realized by inserting an additional insert coil into an otherwise conventional MRI system. System validation was successfully performed with selected iron oxide magnetic nanoparticles and comparison to FFC-NMR relaxometry measurements. Furthermore, we show proof-of-principle R1dispersion imaging and demonstrate the capability of generating R1dispersion contrast at high field with suppressed background signal. With the presented ready-to-use hardware setup it is possible to investigate MRI contrast agents with a strong R1dispersion at a field strength of 3 T
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
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