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Journal of Magnetic Resonance

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https://www.readbyqxmd.com/read/28237893/dynamic-nuclear-polarization-via-thermal-mixing-beyond-the-high-temperature-approximation
#1
W Th Wenckebach
Dynamic Nuclear Polarization (DNP) via the mechanism of thermal mixing has proven itself most powerful for the orientation of nuclear spins in polarized targets and hyperpolarization for magnetic resonance imaging (MRI). Unfortunately, theoretical descriptions of this mechanism have been limited to using-at least partially-the high temperature approximation, in which Boltzmann factors are expanded linearly. However, the high nuclear spin polarization required and obtained for these applications does not justify such approximations...
February 20, 2017: Journal of Magnetic Resonance
https://www.readbyqxmd.com/read/28236786/new-resonator-geometries-for-ice-decoupling-of-loop-arrays
#2
Xinqiang Yan, John C Gore, William A Grissom
RF arrays with a large number of independent coil elements are advantageous for parallel transmission (pTx) and reception at high fields. One of the main challenges in designing RF arrays is to minimize the electromagnetic (EM) coupling between the coil elements. The induced current elimination (ICE) method, which uses additional resonator elements to cancel coils' mutual EM coupling, has proven to be a simple and efficient solution for decoupling microstrip, L/C loop, monopole and dipole arrays. However, in previous embodiments of conventional ICE decoupling, the decoupling elements acted as "magnetic-walls" with low transmit fields and consequently low MR signal near them...
February 16, 2017: Journal of Magnetic Resonance
https://www.readbyqxmd.com/read/28226294/extruded-dielectric-sample-tubes-of-complex-cross-section-for-epr-signal-enhancement-of-aqueous-samples
#3
Jason W Sidabras, Richard R Mett, James S Hyde
This paper builds on the work of Mett and Hyde (2003) and Sidabras et al. (2005) where multiple flat aqueous sample cells placed perpendicular to electric fields in microwave cavities were used to reduce the RF losses and increase the EPR signal. In this work, we present three novel sample holders for loop-gap resonators (LGRs) and cylindrical cavity geometries. Two sample holders have been commissioned and built by polytetrafluoroethylene (PTFE) extrusion techniques: a 1mm O.D. capillary with a septum down the middle, named DoubleDee, and a 3...
February 14, 2017: Journal of Magnetic Resonance
https://www.readbyqxmd.com/read/28222392/endor-with-band-selective-shaped-inversion-pulses
#4
Claudia E Tait, Stefan Stoll
Electron Nuclear DOuble Resonance (ENDOR) is based on the measurement of nuclear transition frequencies through detection of changes in the polarization of electron transitions. In Davies ENDOR, the initial polarization is generated by a selective microwave inversion pulse. The rectangular inversion pulses typically used are characterized by a relatively low selectivity, with full inversion achieved only for a limited number of spin packets with small resonance offsets. With the introduction of pulse shaping to EPR, the rectangular inversion pulses can be replaced with shaped pulses with increased selectivity...
February 12, 2017: Journal of Magnetic Resonance
https://www.readbyqxmd.com/read/28219822/ultrafast-acquisition-of-1-h-1-h-dipolar-correlation-experiments-in-spinning-elastomers
#5
Laetitia Rouger, Maxime Yon, Vincent Sarou-Kanian, Franck Fayon, Jean-Nicolas Dumez, Patrick Giraudeau
We show that two widely used 2D solid-state NMR (ssNMR) pulse sequences can be implemented in an ultrafast (UF) manner, and yield 2D spectra of elastomers in a single scan, under magic-angle spinning. UF 2D ssNMR provides an acceleration of one to several orders of magnitude for classic experiments.
February 9, 2017: Journal of Magnetic Resonance
https://www.readbyqxmd.com/read/28232286/t2-selective-%C3%AF-echo-planar-imaging-for-porous-media-mri
#6
Dan Xiao, Bruce J Balcom
The π Echo Planar Imaging (PEPI) method has recently been modified to permit proton density imaging of fluids in porous media with moderate T2 and short T2(∗) signal components. In many applications, it is desirable to discriminate multiple T2 components within each image voxel. T2 selective imaging is explored in this paper through adiabatic inversion as a magnetization preparation with PEPI readout. When prior information of the sample relaxation times is known, responses of different species to broadband adiabatic inversion pulses can be predicted by Bloch equation simulation...
February 8, 2017: Journal of Magnetic Resonance
https://www.readbyqxmd.com/read/28213048/low-field-single-sided-nmr-for-one-shot-1d-mapping-application-to-membranes
#7
Patrick Judeinstein, Filippo Ferdeghini, Rodrigo Oliveira-Silva, Jean-Marc Zanotti, Dimitrios Sakellariou
Many single-sided permanent magnet NMR systems have been proposed over the years allowing for 1D proton-density profiling, diffusion measurements and relaxometry. In this manuscript we make use of a recently published unilateral magnet for low-field NMR exhibiting an extremely uniform magnetic field gradient with moderate strength and cylindrical symmetry, allowing for a well-defined sweet spot. Combined with a goniometer, our system is used to characterize precisely the uniformity of its gradient and to achieve micrometric precision 1D profiling, as well as spatially localized relaxometry and diffusometry on thick (∼150μm) membrane samples...
February 8, 2017: Journal of Magnetic Resonance
https://www.readbyqxmd.com/read/28189033/corrigendum-to-multiple-quantum-spin-counting-in-magic-angle-spinning-nmr-via-low-power-symmetry-based-dipolar-recoupling-j-magn-reson-236-2013-31-40
#8
Gholamhasan Teymoori, Bholanath Pahari, Elumalai Viswanathan, Mattias Edén
No abstract text is available yet for this article.
February 8, 2017: Journal of Magnetic Resonance
https://www.readbyqxmd.com/read/28189087/a-ferromagnetic-shim-insert-for-nmr-magnets-towards-an-integrated-gyrotron-for-dnp-nmr-spectroscopy
#9
Herbert Ryan, Jan van Bentum, Thorsten Maly
In recent years high-field Dynamic Nuclear Polarization (DNP) enhanced NMR spectroscopy has gained significant interest. In high-field DNP-NMR experiments (⩾400MHz (1)H NMR, ⩾9.4T) often a stand-alone gyrotron is used to generate high microwave/THz power to produce sufficiently high microwave induced B1e fields at the position of the NMR sample. These devices typically require a second, stand-alone superconducting magnet to operate. Here we present the design and realization of a ferroshim insert, to create two iso-centers inside a commercially available wide-bore NMR magnet...
February 5, 2017: Journal of Magnetic Resonance
https://www.readbyqxmd.com/read/28189995/application-of-geometric-approximation-to-the-cpmg-experiment-two-and-three-site-exchange
#10
Fa-An Chao, R Andrew Byrd
The Carr-Purcell-Meiboom-Gill (CPMG) experiment is one of the most classical and well-known relaxation dispersion experiments in NMR spectroscopy, and it has been successfully applied to characterize biologically relevant conformational dynamics in many cases. Although the data analysis of the CPMG experiment for the 2-site exchange model can be facilitated by analytical solutions, the data analysis in a more complex exchange model generally requires computationally-intensive numerical analysis. Recently, a powerful computational strategy, geometric approximation, has been proposed to provide approximate numerical solutions for the adiabatic relaxation dispersion experiments where analytical solutions are neither available nor feasible...
February 4, 2017: Journal of Magnetic Resonance
https://www.readbyqxmd.com/read/28189994/molecular-dynamics-simulations-of-nmr-relaxation-and-diffusion-of-bulk-hydrocarbons-and-water
#11
Philip M Singer, Dilip Asthagiri, Walter G Chapman, George J Hirasaki
Molecular dynamics (MD) simulations are used to investigate (1)H nuclear magnetic resonance (NMR) relaxation and diffusion of bulk n-C5H12 to n-C17H36 hydrocarbons and bulk water. The MD simulations of the (1)H NMR relaxation times T1,2 in the fast motion regime where T1=T2 agree with measured (de-oxygenated) T2 data at ambient conditions, without any adjustable parameters in the interpretation of the simulation data. Likewise, the translational diffusion DT coefficients calculated using simulation configurations agree with measured diffusion data at ambient conditions...
February 3, 2017: Journal of Magnetic Resonance
https://www.readbyqxmd.com/read/28167399/adapted-mr-velocimetry-of-slow-liquid-flow-in-porous-media
#12
Li Huang, Gerd Mikolajczyk, Ekkehard Küstermann, Michaela Wilhelm, Stefan Odenbach, Wolfgang Dreher
MR velocimetry of liquid flow in opaque porous filters may play an important role in better understanding the mechanisms of deep bed filtration. With this knowledge, the efficiency of separating the suspended solid particles from the vertically flowing liquid can be improved, and thus a wide range of industrial applications such as wastewater treatment and desalination can be optimized. However, MR velocimetry is challenging for such studies due to the low velocities, the severe B0 inhomogeneity in porous structures, and the demand for high spatial resolution and an appropriate total measurement time during which the particle deposition will change velocities only marginally...
January 27, 2017: Journal of Magnetic Resonance
https://www.readbyqxmd.com/read/28157560/time-domain-shape-of-electron-spin-echo-signal-of-spin-correlated-radical-pairs-in-polymer-fullerene-blends
#13
Alexander A Popov, Ekaterina A Lukina, Leonid Rapatskiy, Leonid V Kulik
Temporal shape of electron spin echo (ESE) signal of photoinduced spin-correlated radical pairs (SCRP) in composite of conductive polymer P3HT and substituted fullerene PCBM is studied in details. ESE signals of radical pairs (RP) P3HT(+)/PCBM(-) are calculated in realistic model, taking into account finite microwave pulse length. Inhomogeneous broadening of resonant lines and interradical distance distribution are included. Experimentally observed ESE time-domain shape was found to contradict predictions of conventional SCRP theory, which would be valid in the case of very fast electron transfer...
January 23, 2017: Journal of Magnetic Resonance
https://www.readbyqxmd.com/read/28183024/high-field-hyperpolarization-exsy-experiment-for-fast-determination-of-dissociation-rates-in-sabre-complexes
#14
Niels K J Hermkens, Martin C Feiters, Floris P J T Rutjes, Sybren S Wijmenga, Marco Tessari
SABRE (Signal Amplification By Reversible Exchange) is a nuclear spin hyperpolarization technique based on the reversible concurrent binding of small molecules and para-hydrogen (p-H2) to an iridium metal complex in solution. At low magnetic field, spontaneous conversion of p-H2 spin order to enhanced longitudinal magnetization of the nuclear spins of the other ligands occurs. Subsequent complex dissociation results in hyperpolarized substrate molecules in solution. The lifetime of this complex plays a crucial role in attained SABRE NMR signal enhancements...
January 21, 2017: Journal of Magnetic Resonance
https://www.readbyqxmd.com/read/28183023/molecular-dynamics-based-selectivity-for-fast-field-cycling-relaxometry-by-overhauser-and-solid-effect-dynamic-nuclear-polarization
#15
Oliver Neudert, Carlos Mattea, Siegfried Stapf
In the last decade nuclear spin hyperpolarization methods, especially Dynamic Nuclear Polarization (DNP), have provided unprecedented possibilities for various NMR techniques by increasing the sensitivity by several orders of magnitude. Recently, in-situ DNP-enhanced Fast Field Cycling (FFC) relaxometry was shown to provide appreciable NMR signal enhancements in liquids and viscous systems. In this work, a measurement protocol for DNP-enhanced NMR studies is introduced which enables the selective detection of nuclear spin hyperpolarized by either Overhauser effect or solid effect DNP...
January 21, 2017: Journal of Magnetic Resonance
https://www.readbyqxmd.com/read/28152435/nmr-spin-lock-induced-crossing-slic-dispersion-and-long-lived-spin-states-of-gaseous-propane-at-low-magnetic-field-0-05t
#16
Danila A Barskiy, Oleg G Salnikov, Alexey S Romanov, Matthew A Feldman, Aaron M Coffey, Kirill V Kovtunov, Igor V Koptyug, Eduard Y Chekmenev
When parahydrogen reacts with propylene in low magnetic fields (e.g., 0.05T), the reaction product propane develops an overpopulation of pseudo-singlet nuclear spin states. We studied how the Spin-Lock Induced Crossing (SLIC) technique can be used to convert these pseudo-singlet spin states of hyperpolarized gaseous propane into observable magnetization and to detect (1)H NMR signal directly at 0.05T. The theoretical simulation and experimental study of the NMR signal dependence on B1 power (SLIC amplitude) exhibits a well-resolved dispersion, which is induced by the spin-spin couplings in the eight-proton spin system of propane...
January 21, 2017: Journal of Magnetic Resonance
https://www.readbyqxmd.com/read/28135589/longitudinal-gradient-coils-with-enhanced-radial-uniformity-in-restricted-diameter-single-current-and-multiple-current-approaches
#17
Javier A Romero, Gabriela A Domínguez, Esteban Anoardo
An important requirement for a gradient coil is that the uniformity of the generated magnetic field gradient should be maximal within the active volume of the coil. For a cylindrical geometry, the radial uniformity of the gradient turns critic, particularly in cases where the gradient-unit has to be designed to fit into the inner bore of a compact magnet of reduced dimensions, like those typically used in fast-field-cycling NMR. In this paper we present two practical solutions aimed to fulfill this requirement...
January 21, 2017: Journal of Magnetic Resonance
https://www.readbyqxmd.com/read/28157561/indirect-detection-of-infinite-speed-mas-solid-state-nmr-spectra
#18
Frédéric A Perras, Amrit Venkatesh, Michael P Hanrahan, Tian Wei Goh, Wenyu Huang, Aaron J Rossini, Marek Pruski
Heavy spin-1/2 nuclides are known to possess very large chemical shift anisotropies that can challenge even the most advanced magic-angle-spinning (MAS) techniques. Wide manifolds of overlapping spinning sidebands and insufficient excitation bandwidths often obfuscate meaningful spectral information and force the use of static, low-resolution solid-state (SS)NMR methods for the characterization of materials. To address these issues, we have merged fast-magic-angle-turning (MAT) and dipolar heteronuclear multiple-quantum coherence (D-HMQC) experiments to obtain D-HMQC-MAT pulse sequences which enable the rapid acquisition of 2D SSNMR spectra that correlate isotropic (1)H chemical shifts to the indirectly detected isotropic "infinite-MAS" spectra of heavy spin-1/2 nuclides...
January 18, 2017: Journal of Magnetic Resonance
https://www.readbyqxmd.com/read/28119215/novel-methodology-for-accurate-resolution-of-fluid-signatures-from-multi-dimensional-nmr-well-logging-measurements
#19
Vivek Anand
A novel methodology for accurate fluid characterization from multi-dimensional nuclear magnetic resonance (NMR) well-logging measurements is introduced. This methodology overcomes a fundamental challenge of poor resolution of features in multi-dimensional NMR distributions due to low signal-to-noise ratio (SNR) of well-logging measurements. Based on an unsupervised machine-learning concept of blind source separation, the methodology resolves fluid responses from simultaneous analysis of large quantities of well-logging data...
January 12, 2017: Journal of Magnetic Resonance
https://www.readbyqxmd.com/read/28110117/an-adaptive-method-for-determining-an-acquisition-parameter-t0-in-a-modified-cpmg-sequence
#20
Donghui Xing, Yiren Fan, Jianfei Hao, Xinmin Ge, Chaoliu Li, Yufeng Xiao, Fei Wu
The modified CPMG (Carr-Purcell-Meiboom-Gill) pulse sequence is a common sequence used for measuring the internal magnetic field gradient distribution of formation rocks, for which t0 (the duration of the first window) is a key acquisition parameter. In order to obtain the optimal t0, an adaptive method is proposed in this paper. By studying the factors influencing discriminant factor σ and its variation trend using T2-G forward numerical simulation, it is found that the optimal t0 corresponds to the maximum value of σ...
January 9, 2017: Journal of Magnetic Resonance
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