The Slice

For a given half width at half maximum in the time domain, Ar,.n =2, /, the slice width A decreases with increasing gradient strength G. ... 

Closer examination of equation B 1,14,3 reveals that, after the slice selection pulse, the spin isocln-omats at different positions in the gradient direction are not in phase. Rather they are rotated by i exp jyC. )tind... 

Once a slice has been selected and excited, it is necessary to encode the ensuing NMR signal with the coordinates of nuclei within the slice. For each coordinate (x andy) this is achieved by one of two very closely related means, frequency encoding or phase encoding [1]. In this section we consider the fonner and in the next, the latter. In tlie section after that we show how the two are combined in the most coimnon imaging experiment. 

As before, we note that the resonance frequency of a nucleus at position r is directly proportional to the combined applied static and gradient fields at that location. In a gradient G=G u, orthogonal to the slice selection gradient, the nuclei precess (in the usual frame rotating at coq) at a frequency ciD=y The observed signal therefore contains a component at this frequency witli an amplitude proportional to the local spin density. The total signal is of the fomi... 

There is of course no requirement to confine the slice selection to the z-gradient. The gradients may be used in any combination and an image plane selected in any orientation without recourse to rotating the sample. 

Figure Bl.14.5. J2-weighted images of the propagation of chemical waves in an Mn catalysed Belousov-Zhabotinsky reaction. The images were acquired in 40 s intervals (a) to (1) using a standard spin echo pulse sequence. The slice thickness is 2 nun. The diameter of the imaged pill box is 39 nun. The bright bands...

Figure Bl.14.10. Flow tlirough an KENICS mixer, (a) A schematic drawing of the KENICS mixer in which the slices selected for the experiment are marked. The arrows indicate the flow direction. Maps of the z-component of the velocity at position 1 and position 2 are displayed in (b) and (c), respectively, (d) and (e) Maps of the v- and the y-velocity component at position 1. The FOV (field of view) is 10 nnn. (From [31].)...

The slice thickness is proportional to the wavelengdi of the light and a fiinction of the aperture angle. For X = 0.5 pm, the slice thickness is about 0.25 pm for a = nil. Obviously, the point spread fiinction serves also to... 

The first of these problems involves relative motion between a rigid sphere and a liquid as analyzed by Stokes in 1850. The results apply equally to liquid flowing past a stationary sphere with a steady-state (subscript s) velocity v or to a sphere moving through a stationary liquid with a velocity -v the relative motion is the same in both cases. If the relative motion is in the vertical direction, we may visualize the slices of liquid described above as consisting of... 

Subsequent to stock preparation and proper dilution, the paper furnish usually is fed to the paper machine through one or more screens or other devices to remove dirt and fiber bundles. It then enters a flow spreader which provides a uniform flowing stream and which is the width of the paper machine. The flow spreader, or manifold, discharges the slurry into a headbox, where fiber flocculation is minimised by microturbulence and where the proper pressure head is provided to cause the slurry to flow at the proper velocity through the slice and onto the moving Fourdrinier wire. 

The sliced sheet will still contain large quantities of alcohol and it is necessary to season the sheet at elevated temperatures. This may only take three days at 49°C for 0.010 in (0.025 cm) thick sheet but will take about 56 days for 1 in (2.5 cm) thick blocks. The removal of alcohol, as might be expected, is accompanied by considerable shrinkage. Fully seasoned sheet has a volatile content of 2%, the bulk of which is water but there is some residual alcohol. The sheet may be fully polished by heating in a press between glazed plates under pressure for a few minutes. Because the material is thermoplastic it is necessary to cool it before removal from the press. 

Thus, the net change in mass per unit time in the slice (dx) thick will be... 

The darkest regions in the slices indicate the greatest electron density. The meta form of nitrated chlorobenzene and the para form of nitrated nitrobenzene retain the resonance structure to a much greater degree throughout the extent of the electron density. In contrast, the density in the less-favored conformations becomes more localized on the substituent as one moves outward from the plane of the carbon atoms. 

Place all the ingredients except the soda water and orange slice in a cocktail shaker filled with ice. Shake until the egg white froths. Strain into a Collins glass filled with ice. Top with soda water and garnish with the slice of orange. 

For image slicers, contiguous slices of the sky are re-arranged end-to-end to form the pseudo-slit. In that case it is obvious that the sky can be correctly sampled (according to the Nyquist sampling theorem) by the detector pixels on which the slices are projected in the same way as required for direct imaging. 

Figure 8.5 The slice plots taken at (a) 8 4.52 and (b) 8 3.39 of HOHAHA spectra of 3a-hydroxylupanine.

One approach, and the first to be adopted, is to study transmitter release from slices which have been preloaded with radiolabelled transmitter. In these experiments, drug-induced changes in the release of transmitter is usually monitored using the doublepulse technique. This involves comparing the effects of a test drug on the amount of transmitter released in response to a reference pulse and a second identical test pulse. If all the radiolabelled transmitter that overflows in the effluent is collected, and the amount which remains in the slice at the end of the experiment is also measured, it is possible to calculate not only how much radiolabelled transmitter was originally contained in the slice but also the effects of drugs on fractional release , i.e. the proportion of the store of radiolabelled transmitter which is released by nerve stimulation. As with... 

Modern sensitive chromatographic and voltammetric techniques now make it possible to estimate the release of unlabelled endogenous transmitter from slices of brain tissue (commonly the hippocampus and striatum) or spinal cord (Fig. 4.4). However, whatever analytical method is used, the thickness of the slice is paramount. It is important to maintain the balance between preserving the integrity of the tissue (the thicker the slice, the better) against maintaining tissue viability by perfusion with oxygenated aCSF (the thinner the slice, the better). 

ANSWER That is Lacey et al., Allan North s group. It was published in the Journal of Physiology last year. It was also an abstract in the Society 2 years ago. It is the consequence of that application of the agonists, recording intracellularly in the slice of the dopamine neuron. He gets the same thing by virtue of application of norepinephrine agonists to noradrene-gic slice preparation. That is a conventional way to create a hyperpolarization of the cell, to increase the potassium conductance, and so forth. 

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