Static gradient

The D-T2 experiments were performed [51] for a Berea sandstone sample at a proton Larmor frequency of 1.74 MHz and a static gradient of 13 G cm-1. The sample was first vacuum saturated with brine, then centrifuged when immersed in oil resulting in a saturated mixture of oil and water. A D-T2 map was obtained using FLI, shown in Figure 2.7.5. The T2 and D distributions were obtained by... 

Neutrophils may move at speeds of up to 20 /tm min-1 in response to chemoattractants such as denatured proteins, lipids, peptides or C5a. Movement may be defined either as chemokinesis, which is generalised (non-directional) locomotive activity, or as chemotaxis, which is orientation and directional migration up a concentration gradient. A concentration difference at opposite ends of the cell of only 1% is sufficient to activate such directional movement. However, neutrophils do not respond chemotactical-ly to static gradients of chemoattractants, and both temporal and directional changes in chemoattractant concentrations are required. 

M.D. Hurlimann, L. Burcaw, and Y.-Q. Song, Quantitative characterization of food products by two-dimensional D-T2 and T1-T2 distribution functions in a static gradient, J. Colloid Interface Sci., 297, 303-311 (2006). 

D. A vertical sieve tube has a static gradient in the absence of flow and due to gravity of -0.01 MPa m-1. The gradient leading to flow would be either -0.01 MPa m-1 (upward) or -0.03 MPa m-1 (downward). Thus, Jv is either half that in B, namely, 0.3 m hour-1 upward, or 0.9 m hour-1 downward. 

The Hahn and the stimulated echo are used to study molecular self-diffusion in fluids with field gradients which are active during the pulse sequence [Cal2, Karl, Kiml, Stil]. These gradients can be static [Hahl] or pulsed [Stel]. For a static gradient of known magnitude G the self-diffusion constant D can be determined from the amplitude Hahn echo as a function of the echo time t [Hahl, Carl],... 

Fig. 8.4.2 Proton multi-quantum spectra (bottom) of an adamantane phantom (top) without (a) and with (b) application of a static gradient of 48 mT/m. Evolution time and phase of the preparation pulse sequence were incremented in 32 steps of 0.1 p,s and 2 r/32, respectively. Only even-order multi-quantum coherences were detected. The signals from orders 8 through 14 are also displayed on an expanded scale. The multi-quantum spectra demonstrate the increase in the spatial resolution of the two cylinders with increasing coherence order p. Adapted from [Garl] with permission from the American Physical Society.

Fig. 5.5. The magic-echo excitation The durations indicated by a are spin-lock pulses with nominal flip angles of multiples of 360°. The magic echo forms after 6t. Static gradients can be applied during the windows marked by Go, while rf gradients may be effective during G,.

In the case of gradient elution the low flow rates required a considerable reduction of the retardation volume between static gradient mixer and column head and photodiode... 

Zielinski, L.J. and Huerlimann, M.D. 2005. Probing short length scales with restricted diffusion in a static gradient using the CPMG sequence. J. Magn. Reson. 172 161-167. 

SGSE, static gradient spin-echo PGSE, pulsed gradient spin-echo. 

Figure 2 Plots of the calculated normalized echo intensity in the absence of relaxation and diffusion for the ODD sequence (top, circles) and the EVEN sequence (bottom, triangles) versus echo number following a train of 90° pulses. The first echo intensity is the same for each sequence and is governed only by T2 in the absence of diffusion. Subsequent echoes have contributions from T,. The EVEN repeating pattern has two points up and two points down for 90°. Reproduced with permission from Bain AD and Randall EW (1996) Spin echoes in static gradients following a series of 90 degree pulses. Journal of Magnetic Resonance A123 49-55.

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