Southeast drought conditions have accentuated the demand for irrigation in the face of restricted water supply. For allocating this supply, Georgia held an auction for withdrawing irrigated acreage. This auction withdrew 33,000 acres from irrigation, resulting in a physical estimate of a 399 acre-feet daily increase in water flow. The actual reduction is driven by crop distributional changes on the basis of economic substitution and expansion effects. In contrast to the physical estimates, an econometric model that considers these effects is developed. The differences between the physical and econometric models result in an increase in the estimate of water savings of around 19% to 24%.

Topics relevant to modeling and control of mobile wheeled robots with a differential drive are discussed by assuming a motion that is planar and free from lateral and longitudinal slippages, and by taking into account dynamic and kinematic properties of the vehicle. Based on the concept of geometric path-tracking, a controller is designed that is a memoryless function of the lateral, heading, and velocity path-tracking offsets. If these offsets are kept small and the assigned tracking velocity is constant, then this controller may be given a linear, time-invariant and decoupled PID (Proportional + integral + derivative) structure.

The use of T7 RNA polymerase to prepare large quantities of RNA of a particular sequence has greatly facilitated the study of both the structure and function of RNA. Generally, it has been believed that the products of this technique are highly homogeneous in sequence, with only a few noted exceptions. We have carefully examined the transcriptional products of several tRNAs that vary in their 5′ end sequence and found that, for those molecules that begin with multiple, consecutive guanosines, the transcriptional products are far from homogenous. Although a template beginning with GCG showed no detectable 5′ end heterogeneity, two tRNA templates designed to have either four or five consecutive guanosines at their 5′ ends had more than 30% of their total transcriptional products extended by at least one untemplated nucleotide at their 5′ end. By simply reducing the number of consecutive guanosines, the heterogeneity was reduced significantly. The presence of this 5′ end heterogeneity in combination with the 3′ end heterogeneity common to T7 transcriptions results in a mixture of RNA molecules even after rigorous size purification.