Study of triacylglycerol polymorphs by nuclear magnetic resonance: effects of temperature and chain length on relaxation parameters

2008 ◽  
Vol 46 (6) ◽  
pp. 550-557 ◽  
Author(s):  
M. Adam-Berret ◽  
C. Rondeau-Mouro ◽  
A. Riaublanc ◽  
F. Mariette
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Chain Length ◽  
Resonance Effects ◽  
Relaxation Parameters ◽  
Effects Of Temperature ◽  
Nuclear Magnetic

Frequency cycling for compensation of undesired off-resonance effects in surface nuclear magnetic resonance

Geophysics ◽  
2016 ◽  
Vol 81 (4) ◽  
pp. WB33-WB48 ◽  
Author(s):  
Denys Grombacher ◽  
Mike Müller-Petke ◽  
Rosemary Knight
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Larmor Frequency ◽  
Forward Model ◽  
Resonance Excitation ◽  
Entire Volume ◽  
Resonance Effects ◽  
Aquifer Properties ◽  
The Impact ◽  
Nuclear Magnetic

To produce reliable estimates of aquifer properties using surface nuclear magnetic resonance (NMR), an accurate forward model is required. The standard surface NMR forward model assumes that excitation occurs through a process called on-resonance excitation, which occurs when the transmit frequency is set to the Larmor frequency. However, this condition is often difficult to satisfy in practice due to the challenge of accurately determining the Larmor frequency within the entire volume of investigation. As such, in situations where an undesired offset is present between the assumed and true Larmor frequency, the accuracy of the forward model is degraded. This is because the undesired offset leads to a condition called off-resonance excitation, which impacts the signal amplitude, phase, and spatial distribution in the subsurface, subsequently reducing the accuracy of surface NMR estimated aquifer properties. Our aim was to reduce the impact of an undesired offset between the assumed and true Larmor frequency to ensure an accurate forward model in the presence of an uncertain Larmor frequency estimate. We have developed a methodology where data are collected using two different transmit frequencies, each an equal magnitude above and below the assumed Larmor frequency. These data are combined, through a method we refer to as frequency cycling, in a manner that allow the component well-described by our estimate of the Larmor frequency to be stacked coherently, whereas the component related to the presence of an undesired offset is combined destructively. In synthetic and field studies, we have determined that frequency cycling is able to mitigate the influence of an undesired offset providing more accurate estimates of aquifer properties. Furthermore, the frequency-cycling method stabilized the complex inversion of surface NMR data, allowing advantages associated with complex inversion to be exploited.

scholarly journals Effects of temperature on Rb and 129Xe spin polarization in a nuclear magnetic resonance gyroscope with low pump power

AIP Advances ◽  
2017 ◽  
Vol 7 (11) ◽  
pp. 115101 ◽  
Author(s):  
Linlin Chen ◽  
Binquan Zhou ◽  
Guanqun Lei ◽  
Wenfeng Wu ◽  
Yueyang Zhai ◽  
...  
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Pump Power ◽  
Magnetic Resonance ◽  
Spin Polarization ◽  
Effects Of Temperature ◽  
Nuclear Magnetic

The Nuclear Magnetic Resonance Spectra of Compounds Related to DDT. I. Non-Aromatic Protons

1965 ◽  
Vol 19 (5) ◽  
pp. 150-154 ◽  
Author(s):  
Norman E. Sharpless ◽  
Robert B. Bradley
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Chemical Shift ◽  
Chain Length ◽  
Structural Changes ◽  
Coupling Constants ◽  
Limiting Behavior ◽  
Nuclear Magnetic Resonance Spectra ◽  
Magnetic Resonance Spectra ◽  
Nuclear Magnetic

The nuclear magnetic resonance spectra of a series of compounds related to DDT have been studied as they are influenced by ring or aliphatic substituents or by aliphatic structural changes The chemical shift of the benzylic or α proton follows the Hammett equation for ring substituents and the Taft variation of this equation for aliphatic substituents. Alkoxy substituents on the ring show alternation of chemical shift of the —OCH2— group protons with chain length and limiting behavior of the terminal methyl group with chain length. Dehydrochlorination of o,p-DDD produces cis-trans isomers. Coupling constants are shown to be influenced by ring substitution, particularly ortho chlorine.

Fluorine Nuclear Magnetic Resonance Shielding inp-Substituted Fluorobenzenes. The Influence of Structure and Solvent on Resonance Effects

1963 ◽  
Vol 85 (20) ◽  
pp. 3146-3156 ◽  
Author(s):  
Robert W. Taft ◽  
Elton. Price ◽  
Irwin R. Fox ◽  
Irwin C. Lewis ◽  
K. K. Andersen ◽  
...  
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Resonance Effects ◽  
Nuclear Magnetic
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