Spin transfer coefficients

There is an approximately linear relationship between Rv and spin transfer coefficients determined from electron and nuclear magnetic resonance and neutron diffraction, i.e., a contraction of the unit cell accompanies the transfer of spin from transition metal to the ligands. 

The computation of spin transfer coefficients (f s) and ligand field splittings (A) has been pursued particularly actively for NiFe , starting with the pioneering work of Sugano and Shulman (90). Wachters and Nieuwpoort (91) discuss the... 

Table 4. Spin transfer coefficients for Cr3+ in fluoride and oxide lattices...

Observed spin transfer coefficients for Mn2+ and Fe + are given in Tables 6 to 8 and individual /<, and for Mn2+ and Fe + in oxide and fluoride coordination, derived from the combination of LHFI and neutron data are given in Tables 7 and 8. In addition to the data given in the Tables, the neutron data for Sr2Fe20s... 

Table 6. Spin transfer coefficients for Mn2+ in chalgogenide lattices determined by neutron diffraction...

RELATIONSHIP OF /<, TO FRACTIONAL SPIN TRANSFER COEFFICIENTS FOR SOME TRANSITION METAL IONS... 

Relaxation times, MT ratios, and diffusion properties allow insight into the microstructure of various tissues. Determination of these parameters is possible by recording and analysing of a series of volume selective spectra, even for metabolites with relatively low concentrations in vivo. For recording series of spectra usually one parameter is changeable (e.g., inversion time TI for Ti measurements, echo time TE for T2 measurements, MT preparation for assessment of spin transfer and chemical reaction rates, or diffusion sensitizing gradients for assessment of apparent diffusion coefficients or even diffusion... 

In the 1950s Hickman developed a centrifugal vapor compression evaporator for seawater desalination (53). This device consisted of multiple spinning discs. Seawater sprayed on one side of the disc evaporated, while the centrifugal force removed the residue from the plate surface. The vapor was compressed and returned to the opposite side of the plate, where condensation provided the heat for evaporation and the desired freshwater for recovery. Overall heat transfer coefficients of 18 kW/m2-K are about three times higher than those achieved in steam turbine condensers. 

Unlike correlation spectroscopy based on spin diffusion, the adiabatic version enables, in principle, almost full exchange of magnetization between the two spins. As a result, the entire signal intensity will reside in the cross-peaks. Violation of the adiabaticity is characterized by the appearance of a diagonal peak and can be expected to occur if the rotation sweep is too fast compared to the interaction between spins. While numerical simulations indicate possible linear dependencies of the polarization transfer coefficient on spin coupling and the rate of the sweep over a range of practical values, the validity of this assumption remains to be tested. Here we present a semi-quantitative example of a relayed polarization transfer process. 

The dynamics of the rotor speed can be conveniently analysed and adjusted by feeding a signal from the rotor motion monitor (via an optical fibre) to a console ADC (Fig. 7). The corresponding spectra are shown in Fig. 8. The faster sweep clearly reduces K12, and to a lesser extent K13. Both direct complementary peaks (1-Kmn) and relayed peaks depend on the product of complementary transfer coefficients, and correlate well with the expected influence of the sweep rate variation. The observed relay process can be shorted by proton-driven spin diffusion. Consequently, efficient rotation-speed independent (or carefully synchronized) decoupling is required during the entire mixing period. 

This assumes that a chemical species is penetrating into a static film over a time period of t with a diffusiv-ity in the liquid of D. If it is assumed that the exposure time constant t in the equation is equal to the residence time of the liquid on a spinning disk surface, given by Eq. (6), then the liquid-side mass transfer coefficient LG for diffusion into the film can be estimated as... 

For a spinning disk, the standard model for falling film flow is complicated by the changing thickness and shear as the liquid flows over the disk. An approximation of this to conditions on a spinning disk surface can, however, be made by substitution of Eq. (9) for average liquid-solid surface shear into the above equation for mass transfer. If it is also assumed that the characteristic distance L traveled by the liquid is equal to that of the disk radius then an equation for the liquid-solid mass transfer coefficient ls can be written for an SDR as... 

In order to improve the heat transfer in a reactor, use can be made of gravitational forces. This concept is used in the spinning disc reactor (SDR) as developed at Newcastle University. The reaction mixture flows in a thin layer in axial direction over a rotating disc. A typical heat transfer coefficient is 10 kW/m2K. This reactor however is dedicated for liquid-liquid reactions. Especially condensation reactions can be enhanced by removing the gaseous by-products thus shifting the chemical equilibrium to the right. 

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