Recognition of moving objects using feature signatures

An important application of machine vision systems is the recognition of known three-dimensional objects. A major difficulty arises when two or more objects project the same or similar two-dimensional image, often resulting in misclassification and degradation of system performance. The changes in images which result from the motion of objects provide a source of three-dimensional information which can greatly aid the classification process, but this three-dimensional analysis is computationally complex and subject to many sources of error. This work develops a methodology which utilizes the information derived from the apparent changes in object features over time to facilitate the recognition task, without the need to actually recover the three-dimensional structure of the objects under view. The basic approach is to generate a ``feature signature' by combining the feature measurements of the individual regions in a long sequence of images. The static information in the individual frames is analyzed along with the temporal information from the entire sequence. These techniques are particularly applicable in situations where static image processing methods cannot discriminate between ambiguous objects. Two example implementations are presented to illustrate the application of the techniques of object recognition using motion information.     

Structural and kinetic studies on ligand binding in wild-type and active-site mutants of penicillin acylase

Penicillin acylase catalyses the condensation of Calpha-substituted phenylacetic acids with beta-lactam nucleophiles, producing semi-synthetic beta-lactam antibiotics. For efficient synthesis a low affinity for phenylacetic acid and a high affinity for Calpha-substituted phenylacetic acid derivatives is desirable. We made three active site mutants, alphaF146Y, betaF24A and alphaF146Y/betaF24A, which all had a 2- to 10-fold higher affinity for Calpha-substituted compounds than wild-type enzyme. In addition, betaF24A had a 20-fold reduced affinity for phenylacetic acid. The molecular basis of the improved properties was investigated by X-ray crystallography. These studies showed that the higher affinity of alphaF146Y for (R)-alpha-methylphenylacetic acid can be explained by van der Waals interactions between alphaY146:OH and the Calpha-substituent. The betaF24A mutation causes an opening of the phenylacetic acid binding site. Only (R)-alpha-methylphenylacetic acid, but not phenylacetic acid, induces a conformation with the ligand tightly bound, explaining the weak binding of phenylacetic acid. A comparison of the betaF24A structure with other open conformations of penicillin acylase showed that betaF24 has a fixed position, whereas alphaF146 acts as a flexible lid on the binding site and reorients its position to achieve optimal substrate binding.