305,132 research outputs found
Mobility of sodium ions in agarose gels probed through combined single- and triple-quantum NMR
Full text linkFunder:
http://dx.doi.org/10.13039/501100001659
Deutsche Forschungsgemeinschaf
Pseudo rotary resonance relaxation dispersion effects in isotropic samples
Full text linkEnhanced transverse relaxation near rotary resonance conditions is a well-documented effect for anisotropic solid samples undergoing magic-angle spinning (MAS). We report transverse signal decay associated with rotary resonance conditions for rotating liquids, a surprising observation, since first-order anisotropic interactions are averaged at a much faster timescale compared with the spinning frequency. We report measurements of 13C and 1H signal intensities under spin lock for spinning samples of polybutadiene rubber, polyethylene glycol solution, and 99.96 % D2O. A drastic reduction in spin-lock signal intensities is observed when the spin-lock frequency matches 1 or 2 times the MAS rate. In addition, oscillations of the signal are observed, consistent with a coherent origin of the effect, a pseudo rotary resonance relaxation dispersion (pseudo-RRD). Through simulations, we qualitatively describe the appearance of pseudo-RRD, which can be explained by time dependence caused by sample rotation and an inhomogeneous field, the origin of which is an instrumental imperfection. Consideration of this effect is important for MAS experiments based on rotary resonance conditions and motivates the design of new MAS coils with improved radio frequency (RF)-field homogeneity
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
Windowed cross polarization at 55 kHz magic-angle spinning
Full text linkCross polarization (CP) transfers via Hartmann-Hahn matching conditions are one of the cornerstones of solid-state magic-angle spinning NMR experiments. Here we investigate a windowed sequence for cross polarization (wCP) at 55 kHz magic-angle spinning, placing one window (and one pulse) per rotor period on one or both rf channels. The wCP sequence is known to have additional matching conditions. We observe a striking similarity between wCP and CP transfer conditions when considering the flip angle of the pulse rather than the rf-field strength applied during the pulse. Using fictitious spin-1/2 formalism and average Hamiltonian theory, we derive an analytical approximation that matches these observed transfer conditions. We recorded data at spectrometers with different external magnetic fields up to 1200 MHz, for strong and weak heteronuclear dipolar couplings. These transfers, and even the selectivity of CP were again found to relate to flip angle (average nutation)
Great Offset Difference Internuclear Selective Transfer
Full text linkCarbon–carbon dipolar recoupling sequences are frequently used building blocks in routine magic-angle spinning NMR experiments. While broadband homonuclear first-order dipolar recoupling sequences mainly excite intra-residue correlations, selective methods can detect inter-residue transfers and long-range correlations. Here, we present the great offset difference internuclear selective transfer (GODIST) pulse sequence optimized for selective carbonyl or aliphatic recoupling at fast magic-angle spinning, here, 55 kHz. We observe a 3- to 5-fold increase in intensities compared with broadband RFDR recoupling for perdeuterated microcrystalline SH3 and for the membrane protein influenza A M2 in lipid bilayers. In 3D (H)COCO(N)H and (H)CO(CO)NH spectra, inter-residue carbonyl–carbonyl correlations up to about 5 Å are observed in uniformly 13C-labeled proteins
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
Author, publisher and bookseller : a tripartite synergy in Nigerian book industry
Full text linkThis work is about the roles of Author, Publisher and Bookseller in Book development in
Nigeria. The paper started by delving into the history of Book Publishing in Nigeria after
which it proceeded by defining who an author, a publisher, and a bookseller is and
expatiated on the indispensable roles of these key actors in Nigerian Book Industry and in
the emerging Information Society. Furthermore, the various constraints to book
development were identified while the paper advised on how the Book Industry can be
further promoted in Nigeria. However, the paper concluded and made recommendations
on how the Book sector can help in enhancing scholarship in the country
[Report to Chief J. E. Curry, by an unknown author #2]
No full textReport to Chief J. E. Curry, by an unknown author. The report contains a list of officers who gave depositions to the United States Attorney
[Report to Chief J. E. Curry, by an unknown author #1]
No full textReport to Chief J. E. Curry, by an unknown author. The report contains a list of officers who gave depositions to the United States Attorney
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