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Spin amplification in solution magnetic resonance using radiation damping
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10.1063/1.2752168
/content/aip/journal/jcp/127/5/10.1063/1.2752168
http://aip.metastore.ingenta.com/content/aip/journal/jcp/127/5/10.1063/1.2752168

Figures

Image of FIG. 1.
FIG. 1.

Using radiation damping to create a sensitive magnetization detector (Ref. 16). The solvent magnetization is inverted along the unstable axis. Any small deviation of away from the axis will generate a radiation damping field that will tilt the solvent magnetization back to the axis. The detector works by utilizing the radiation damping field generated by some dilute solute magnetization to tilt the solvent magnetization away from the axis.

Image of FIG. 2.
FIG. 2.

as a function of the chemical shift difference between solute and solvent for different relative orientations of the solute magnetization with respect to some residual solvent magnetization . In all simulations, , , and . For small , the distribution in is quite small, whereas for larger values of the distribution increases.

Image of FIG. 3.
FIG. 3.

Probability distribution for for different effective solute concentrations . In all simulations, and . In (A), , which gave a resolution in of . In (B), , which gave a resolution in of . The probability distributions peak at later times and become wider with decreasing . Additionally, comparing (B) to (A), the distributions in tend to be peaked at shorter times and are sharper for smaller chemical shift differences due to the fact that the radiation damping field generated by the solute becomes weaker with increasing .

Image of FIG. 4.
FIG. 4.

(A) A selective pulse is first applied to the solute magnetization. Next, a Gaussian gradient of strength and duration winds up the solute magnetization, followed by a time delay of . A broadband 180° pulse is applied in order to invert the solvent magnetization, and another Gaussian gradient of strength and duration are applied in order to crush any residual solvent magnetization arising from imperfect inversion and to rephase the solute magnetization. After the final gradient, the initial conditions of the solute and solvent magnetizations are given in Fig. 1. The diffusion during can effectively attenuate , providing a means to adjust the value of by changing [Eq. (15)]. In (B), same as in (A), but with the addition of a series of bipolar gradients of strength and duration . If , where is an integer, the bipolar gradients can enhance the coupling between the solute and solvent magnetizations via the radiation damping field (Ref. 19).

Image of FIG. 5.
FIG. 5.

The experimental distribution in (A) and (B) phases of the water magnetization for an aqueous acetone solution using the sequence in Fig. 4(a) without the initial selective pulse. Using Eq. (11), and choosing and , the calculated distribution in is plotted (solid line). The calculated distribution gives . The experimentally observed distribution in (for experiments) was . In (B), the phase distribution is essentially scattered randomly over the interval , with the experimentally observed phase distribution being .

Image of FIG. 6.
FIG. 6.

(Color) Experimental distributions for obtained using the pulse sequence in Fig. 4(a) with the selective pulse either centered (A) on the acetone resonance , or (B) centered on the opposite side of the water resonance . The results are summarized in Table I.

Image of FIG. 7.
FIG. 7.

(Color) Experimental distributions for obtained using the pulse sequence in Fig. 4(b) for bipolar gradients applied “on resonance” with respect to the acetone/water shift difference, with giving . The initial selective pulse was either centered (A) on the acetone resonance or (B) at the opposite frequency . The results are summarized in Table II.

Image of FIG. 8.
FIG. 8.

(Color) Experimental distributions for obtained using the pulse sequence in Fig. 4(b) for bipolar gradients applied “off resonance” with respect to the acetone/water shift difference, with giving . The initial selective pulse was either centered (A) on the acetone resonance or (B) at the opposite frequency . The results are summarized in Table III.

Tables

Generic image for table
Table I.

Experimentally observed values of obtained using the pulse sequence in Fig. 4(a) with the selective pulse centered either at (resonant with acetone) or at , for different values of . The experimental distributions are shown in Fig. 6.

Generic image for table
Table II.

Experimentally observed values of obtained using “on resonant" bipolar gradients [pulse sequence in Fig. 4(b)] with the initial selective pulse centered either at (resonant with acetone) or at , for different values of . By choosing the timing of the bipolar gradients to be , the radiation damping field was modulated at a frequency roughly equal to the chemical shift difference between water and acetone . The experimental distributions are shown in Fig. 7.

Generic image for table
Table III.

Experimentally observed values of obtained using an “off resonant" bipolar gradient scheme [pulse sequence in Fig. 4(b)] with the selective pulse centered either at (resonant with acetone) or at , for different values of . By choosing the timing of the bipolar gradient to be , the radiation damping field was modulated at a frequency of , which was less than the chemical shift difference between water and acetone. The experimental distributions are shown in Fig. 8.

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/content/aip/journal/jcp/127/5/10.1063/1.2752168
2007-08-03
2014-04-16
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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Spin amplification in solution magnetic resonance using radiation damping
http://aip.metastore.ingenta.com/content/aip/journal/jcp/127/5/10.1063/1.2752168
10.1063/1.2752168
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