Power gradient

Field programming is the ability to run voltage, current, or power gradients, and it is another feature that is often useful. Although field gradients are not common, they have been used to slow down the migration of an analyte of interest prior to fraction collection. In addition, field... 

After the advent of MR systems with powerful gradient hardware, dynamic scans with a repetition rate of at least one image or image stack per 2 s have become possible. By use of such sequences it has become feasible to visualize the transit of a bolus of paramagnetic or superparamagnetic contrast agent through the brain (Moseley et al. 1990 Rosen et al. 1990). For DSC, the bolus is injected intravenously. 

In order to accommodate these requirements, we have designed and built a one dimensional, high power gradient set. With an efficiency of 1.5 G/cm/A, we can achieve a maximum gradient strength of 300 G/cm with a Techron 8710 power supply. Extensive water cooling allows us to maintain the temperature under 17°C with a maximum sustained current of 140 A. 

For the average core outlet temperature of 500°C, the coolant outlet temperature ranges from about 385 to 602°C. Most of the relatively cold outlet coolant comes from the outer regions of the core. This is due to the power to flow rate mismatches in the outer fuel assemblies which are caused by the large power gradient within the horizontal plane of the outer fuel assemblies. 

P is the critical exponent and t denotes the reduced distance from the critical temperature. In the vicinity of the critical point, the free energy can be expanded in tenns of powers and gradients of the local order parameter m (r) = AW - I bW ... 

The method has severe limitations for systems where gradients on near-atomic scale are important (as in the protein folding process or in bilayer membranes that contain only two molecules in a separated phase), but is extremely powerful for (co)polymer mixtures and solutions [147, 148, 149]. As an example Fig. 6 gives a snapshot in the process of self-organisation of a polypropylene oxide-ethylene oxide copolymer PL64 in aqueous solution on its way from a completely homogeneous initial distribution to a hexagonal structure. 

The integral of the temperature gradient of the spectral power density from wavelength Xl to X2, is readily calculable using the Planck radiation law (5). Constant emissivity is assumed for equation 3. 

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