Rotational-echo double resonance of uniformly labeled 13C clusters

The use of rotational-echo double resonance NMR to measure distances from an observed tightly coupled cluster of 13C spins to a distant 15N, 31P, or 19F is practical if 13C chemical shifts and homonuclear 13C-13C isotropic J interactions are refocused by a combination of rotor-synchronized 13C pi and pi/2 pulses. This scheme is illustrated by experiments performed on diluted and recrystallized L-[13C(3),15N]alanine and L-[13C(6),alpha-15N]histidine.     

Stop-consonant recognition for normal-hearing listeners and listeners with high-frequency hearing loss. II: Articulation index predictions

Articulation index (AI) theory was used to evaluate stop-consonant recognition of normal-hearing listeners and listeners with high-frequency hearing loss. From results reported in a companion article [Dubno et al., J. Acoust. Soc. Am. 85, 347-354 (1989)], a transfer function relating the AI to stop-consonant recognition was established, and a frequency importance function was determined for the nine stop-consonant-vowel syllables used as test stimuli. The calculations included the rms and peak levels of the speech that had been measured in 1/3 octave bands; the internal noise was estimated from the thresholds for each subject. The AI model was then used to predict performance for the hearing-impaired listeners. A majority of the AI predictions for the hearing-impaired subjects fell within +/- 2 standard deviations of the normal-hearing listeners' results. However, as observed in previous data, the AI tended to overestimate performance of the hearing-impaired listeners. The accuracy of the predictions decreased with the magnitude of high-frequency hearing loss. Thus, with the exception of performance for listeners with severe high-frequency hearing loss, the results suggest that poorer speech recognition among hearing-impaired listeners results from reduced audibility within critical spectral regions of the speech stimuli.     

Chromatographic Processing Scheme for Continuous Harvesting of rec-Prourokinase from Serum Free Medium Cell Cultures

Continuous perfusion cell culture, using albumin containing medium, offers the potential advantages of higher recombinant Prourokinase (r-ProUK) yields, higher initial product purity and increased throughput compared to batch culture technology using medium supplemented with fetal bovine serum. We have characterized the production of r-ProUK in medium supplemented with a lipid rich bovine serum albumin (Albumax) in a perfusion system. The results of these studies showed that it was necessary to modify the r-ProUK batch recovery scheme to process r-ProUK from a perfusion system. To accommodate large volumes of perfusate harvested over a ten to fourteen day production cycle, cation exchange and hydrophobic interaction chromatography (HIC) resins were identified that had increased product binding capacity, better flow characteristics and wider pH ranges which allowed caustic cleaning. The mobile phase composition, pH and ionic strength were modified to improve r-ProUK yields from the identified resins, and procedures were developed to eliminate r-ProUK degradation products. Strategies were defined for processing continuous harvest, which contained four to seven times the amount of r-ProUK of batch harvests.