This short animation shows the process of NMR excitation in the laboratory and the rotating frame, as well as the dephasing that occurs from field inhomogeneity and the formation of the Hahn spin echo. Please credit (c)2010 Mark Cohen (mscohen@ucla.edu) during re-use.
From:markcat3t
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[U. of Ottawa NMR Facility Blog] Excitation Profiles for Shaped Pulses
Excitation Profiles for Shaped Pulses
Shaped pulses are very commonly used for selective excitation and nonselective inversion in a large number of NMR pulse sequences. The frequency domain excitation profile of a radio frequency pulse is the Fourier transform of the time dependent pulse shape and determines the width, uniformity and phase of the frequency spectrum excited. Since time and frequency are reciprocals of one another, short rf pulses have very wide excitation profiles and long rf pulses have very narrow selective excitation profiles. In a previous BLOG post the excitation...
nmrlearner
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01-21-2011 03:31 AM
[NMR paper] Transverse dephasing optimized solid-state NMR spectroscopy.
Transverse dephasing optimized solid-state NMR spectroscopy.
Related Articles Transverse dephasing optimized solid-state NMR spectroscopy.
J Am Chem Soc. 2003 Nov 19;125(46):13938-9
Authors: De Paëpe G, Giraud N, Lesage A, Hodgkinson P, Böckmann A, Emsley L
It is shown how coherence lifetimes in solid-state NMR experiments can be controlled. New decoupling schemes are introduced which actively optimize dephasing times, providing increases of up to a factor of 2 with respect to the best existing schemes. The new schemes are implemented in...
nmrlearner
Journal club
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11-24-2010 09:16 PM
[U. of Ottawa NMR Facility Blog] Gradient Spin Echoes for Selective Excitation
Gradient Spin Echoes for Selective Excitation
Shaped excitation pulses can replace the non-selective hard pulses typically used in a one-pulse measurement to achieve selective excitation. Another method of achieving selective excitation is the gradient spin echo using a selective 180° pulse. This technique is demonstrated in the figure below. http://4.bp.blogspot.com/_5wBTR2kKTqA/S_UxeG5oXdI/AAAAAAAAAzc/BHWef-Tse7s/s400/grad_spin_echo.jpgA non-selective hard 90°x pulse is first given followed by a pair of identical pulsed field gradients sandwiching a soft selective 180° pulse about the y...
nmrlearner
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08-21-2010 08:15 PM
[U. of Ottawa NMR Facility Blog] The Dephasing Power of Pulsed Field Gradients
The Dephasing Power of Pulsed Field Gradients
Pulsed field gradients are used in many modern NMR measurements to select specific coherence pathways and eliminate (or at least minimize) the need for time consuming pulse and receiver phase cycles. The gradients are most often used in conjunction with spin echos such that unwanted coherences can be dephased and the desired coherences can be rephased. They are also used to measure diffusion constants or collect DOSY data. It is instructive to examine the magnetization vectors in the active volume of an NMR tube as a function of the gradient...
Introductory NMR & MRI: Video 06: Spin echoes, CPMG and T2 relaxation
Introductory NMR & MRI: Video 06: Spin echoes, CPMG and T2 relaxation
http://i.ytimg.com/vi/B2HMAJQJ7ok/default.jpg
Introductory NMR & MRI: Video 06: Spin echoes, CPMG and T2 relaxation
Paul Callaghan gives an introduction to NMR and MRI. This is the 6th video of a 10 episode series produced by Magritek Ltd.
From: magritek
Views: 7207
http://gdata.youtube.com/static/images/icn_star_full_11x11.gif http://gdata.youtube.com/static/images/icn_star_full_11x11.gif http://gdata.youtube.com/static/images/icn_star_full_11x11.gif...
nmrlearner
NMR educational videos
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08-18-2010 01:38 AM
dipolar dephasing and T2
is dipolar dephasing one of the contributing mechanisms to T2 or they are different ? Thanks
NMR Excitation, Dephasing and Spin Echoes
Linear Mode
