Spin bunching

Fig. 9.13 Time evolution of the NFS intensity for various temperatures around the HS-LS transition of [Fe(tpa)(NCS)2]. The measurements were performed at 1D18, ESRF in hybrid-bunch mode. The left-hand side shows measurements in the transition region performed with decreasing temperature and the right-hand side with increasing temperature. (The spectral patterns at comparable temperatures do not match due to hysteresis in the spin-transition behavior). The points give the measured data and the curves are results from calculations performed with CONUSS [9, 10]. The dashed line drawn in the 133 K spectmm represents dynamical beating. (Taken from [41])...

It is very difficult to describe coherence transfer using the vector model. To understand it we will need to expand our theoretical picture to include product operators. Product operators are a shorthand notation that describes the spin state of a population of spins by dividing it into symbolic components called operators. You might wonder why you would trade in a nice pictorial system for a bunch of equations and symbols. The best reason I can give is that the vector model is useless for describing most of the interesting NMR experiments, and product operators offer a bridge between the familiar vectors and the more formal and... 

As shown in Fig. 3, the decay time 7 of the FID is related to the half-width of the Lorentzian peak. The quantity 1/7 gives a measure of the rate at which the My component decays due to randomization of the bunched individual magnetic moments on the precessional cone. This dephasing involves no energy change and is caused by spin-spin... 

Figure 2.9. Following a 90° pulse, the individual spin vectors bunch along the y-axis and are said to possess phase coherence.

Figure 5.27. Net transverse magnetisation is produced from the bunching of individual magnetic moments which gives rise to an observable NMR signal. These spins are said to posses phase coherence, and because only single-quantum spin transitions (a <-> ) ate involved in generating this state, it is termed single-quantum coherence.

David Foley, a former town planner, decried Plum Creek s dark hints that a denial of its proposal would spell doom for the forest and the region. You could almost admire their audacity if the consequences weren t so devastating.. . . Plum Creek thinks we re a bunch of rubes who just fell off the turnip truck. When you make sense, you don t need battalions of attorneys, spin doctors, and fixers. When you re a straight shooter, you don t need bamboozlement and not-so-subtle threats. ... 

Fig. 127. Self-consistent mean-field calculations of periodic stmctuies in Ho. Each circle represents the magnitude and direction of the ordered moment in a specific plane, relative to the size of the moment at absolute zero (lO/tg), indicated by the length of the horizontal lines. The orientation of moments in adjacent planes is depicted by the positions of the neighbouring circles, (a) The 12-layer zero-spin-slip structure at 4K. The open circle in the centre indicates the ferromagnetic component in the cone structure (b) the 11-layer one-spin-slip structure at 25 K. The bunched pairs of moments are disposed asymmetrically with respect to the easy axis in the vicinity of the spin slip (after Jensen and Mackintosh 1992).

One of the things we discovered was that there were some subtle differences in the surface characteristics of each version. Sometimes this was helpful, as it made easier to attach the foam knee pad to the board, and sometimes it was not. We also began to notice differences in their durability. In an attempt to quantify this, my boss and I hooked up a bunch of samples behind his car, and we drove around the parking lot for 15 min or so, towing the boards behind us, and doing everything we could to make them tumble and spin and bounce and collide. While there was no alcohol involved— and no animals were harmed in the testing—we did have a lot of fiia And we were also able to determine which materials had the best durability. 

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