On the structural integrity of the spinel block in the β"-alumina structure.
The β''-alumina structure is examined in detail and an analysis is presented of the three-dimensional integrity of the lattice. The layer structure that is responsible for the very high sodium conduction rate is the specific focus. Rigid layers that are derived from the cubic spinel structure are interleaved by more open honeycomb pathways where rapid ion diffusion takes place. The three-dimensional rigidity of the spinel block in this structure makes it possible to accurately quantify the conduction layer thickness based only on the hexagonal unit-cell dimensions, as suggested originally by Harbach [(1983), J. Mater. Sci. 18, 2437-2452]. His calculation is tested rigorously against the many single-crystal structure determinations that have been made on the β''-alumina family compounds and excellent correlation is found.
X-Ray and23Na NMR Investigations on Na+– and Na+/La3+–β″-Al2O3Crystals
Abstract The structure of a Na+/La3+–β″-Al2O3crystal (degree of exchange ξ = 80%) has been investigated by conventional single crystal X-ray diffraction methods at room temperature. The lanthanide ions occupy eightfold ccordinated mO (9d) as well as sevenfold coordinated BR sites (6c). Remaining Na+ions were found exclusively in BR positions.23Na NMR measurements were performed at room temperature before and after the exchange procedure. Two distinct23Na signals differing in angular dependence of the second order quadrupole resonance shifts were recorded for the pure Na+–β″-Al2O3crystal whereas in the case of the doped isomorph only one signal was detected. The23Na NMR signals were assigned to the two possible positions for the Na+ions in the conduction planes.
LABORATORY AND FIELD TESTING OF SEED SPACING UNIFORMITY FOR SUGARBEET PLANTERS
Five planter configurations were evaluated for seed spacing uniformity at three field speeds using a seed 
location method in the field and a laboratory method involving an opto-electronic sensor system. Planter seed spacing 
uniformity was described using the Coefficient of Precision (CP3) measure. Results showed that CP3 measures 
determined using the laboratory test method were significantly different from those determined using the field test method. 
This indicated the laboratory test method cannot be used to predict planter seed spacing uniformity in the field. Seed 
spacing uniformity determined in laboratory tests was higher than, or equal to, seed spacing uniformity determined in 
field tests. This indicated the laboratory test method may be useful to screen out planters or planter units with poor 
uniformity of seed metering. Field testing of the planters that perform well in laboratory tests must be conducted to 
adequately determine the seed spacing uniformity of those planters in the field. Results from laboratory and field tests 
could be useful in determining areas for improvement of planters or planter units.