Match condition modulating

Figure 2.24. A. One of the pulse sequences for modulating the Hartmann-Hahn match condition by ramping the X-nucleus transmitter amplitude. B. Comparison of H —> C CP for conventional CP (SACP) matched on the centreband and a sideband with RAMP-CP on a sideband of N-t-Boc-alanine showing the very much improved quantitative data for the six equally populated carbon sites. Taken from Metz, Ziliox and Smith (1996) with permission of the copyright owners.

The first of these arises when the long spin-lock pulse acts in an analogous fashion to the last 90" pulse of the COSY experiment so causing coherence transfer between J-coupled spins. The resulting peaks display the usual antiphase COSY peak stmcture and tend to be weak so are of least concern. A far greater problem arises from TOCSY transfers which arise because the spin-lock period in ROESY is similar to that used in the TOCSY experiment (Section 5.7). This may, therefore, also induce coherent transfers between J-coupled spins when these experience similar rf fields, that is, when the Hartmann-Hahn matching condition is satisfied. Since the ROESY spin-lock is not modulated (i.e. not a composite pulse sequence), this match is restricted to mutually coupled spins with similar chemical shift offsets or to those with equal but opposite... 

As pointed out in the preceding section, the first terms (in square brackets) on the righthand sides of these equations are phase modulation effects caused by the spatially static terms in the optical intensity fimction. Notice that, because of the presence of these phase modulations, the initially perfect phase-matching condition (M=0) will be degraded as these waves interact and propagate deeper into the nonlinear meditun. 

Madan et al. [515] have presented the effect of modulation on the properties of the material (dark conductivity and photoconductivity) and of solar cells. They also observe an increase in deposition rate as a function of modulation frequency (up to 100 kHz) at an excitation frequency of 13.56 MHz, in their PECVD system [159]. The optimum modulation frequency was 68 kHz, which they attribute to constraints in the matching networks. Increasing the deposition rate in cw operation of the plasma by increasing the RF power leads to worse material. Modulation with a frequency larger than 60 kHz results in improved material quality, for material deposited with equal deposition rates. This is also seen in the solar cell properties. The intrinsic a-Si H produced by RF modulation was included in standard p-i-n solar cells, without buffer or graded interface layers. For comparison, solar cells employing layers that were deposited under cw conditions were also made. At a low deposition rate of about 0.2 nm/s, the cw solar cell parameters... 

This procedure involves selecting a fluorophore of known lifetime and placing it in the microscope and measuring the phase and modulation depth [11]. Rearranging Eqs. (2.5 and 2.6) allows the expected phase and modulation to be predicted. These may then be used to compute the position of zero phase and the modulation depth of the light source. An advantage of the method is that it may be done under conditions exactly matching those of a sample. 

The simulated C02 fugacity matches the initial reservoir C02 content and indicates that the pH is buffered by C02-calcite equilibrium. Further modelling was carried out using the Geochemists Workbench React and Tact modules with the thermodynamic database modified to reflect the elevated P conditions and kinetic rate parameters consistent with the Waarre C mineralogy. The Waarre C shows low reactivity and short-term predictive modelling of the system under elevated C02 content changes little with time (Fig. 1). 

The ACTMs results depend on the initial conditions and inflow of background concentrations into the computational domain. For meso and local scale AQ simulations, these conditions are usually defined from larger scale forecast results by an interface module that has to match grid and resolution differences and possibly the different chemical reactions schemes employed in the models considered. 

Upper canopy layer The dominant term in the upper canopy is the effect on the sink of the velocity perturbation through the last term of (5.27), r/2Lc [AuCB. Since Ail peaks at the hillcrest, this produces a minimum in Ac there. This effect can be interpreted as the canopy counterpart of the dominant role played by changes in surface stress on a rough hill in modulating the surface flux boundary condition, and thereby Ac, as discussed earlier. Hence, as a result of quite different dynamics, the dominant influences on Ac in the lower and upper canopy layers are in phase leading to a minimum in Ac at the hillcrest. This simple picture is modulated by other effects in the upper canopy layer, however. The eddy flux divergence couples the upper canopy to the shear stress layer above where advection is important at first order (5.26) and within which the contributions to Ac that are caused by canopy dynamics must decay to match the inviscid, streamline convergence effects around z = hi. 

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