Effects of age and mild hearing loss on speech recognition in noise

Using an adaptive strategy, the effects of mild sensorineural hearing loss and adult listeners' chronological age on speech recognition in babble were evaluated. The signal-to-babble ratio required to achieve 50% recognition was measured for three speech materials presented at soft to loud conversational speech levels. Four groups of subjects were tested: (1) normal-hearing listeners less than 44 years of age, (2) subjects less than 44 years old with mild sensorineural hearing loss and excellent speech recognition in quiet, (3) normal-hearing listeners greater than 65 with normal hearing, and (4) subjects greater than 65 years old with mild hearing loss and excellent performance in quiet. Groups 1 and 3, and groups 2 and 4 were matched on the basis of pure-tone thresholds, and thresholds for each of the three speech materials presented in quiet. In addition, groups 1 and 2 were similar in terms of mean age and age range, as were groups 3 and 4. Differences in performance in noise as a function of age were observed for both normal-hearing and hearing-impaired listeners despite equivalent performance in quiet. Subjects with mild hearing loss performed significantly worse than their normal-hearing counterparts. These results and their implications are discussed.     

Some Models for a Hierarchical Manpower System

This paper is an extension of previous work which described a model for a hierarchical manpower system with two grades. The model is first extended to a system with several grades, and then to a system with several types of entrant or in which the type of entrant has changed over time. Finally, a calculation is described which can be used to determine the best mix of qualifications amongst the entrants.     

Synthesis and in vivo activity of some porphyrindione derivatives with potential in photodynamic therapy

A number of synthetic bacteriochlorins were prepared from porphyrindiones. The potential of these compounds as sensitizers for photodynamic therapy was examined using the FANFT-induced urothelial cell carcinoma (AY-27) transplanted into rats. In a number of cases, tumor regression was significant following treatment with both drug and light.     

Modifications in the alditol acetate method for analysis of muramic acid and other neutral and amino sugars by capillary gas chromatography-mass spectrometry with selected ion monitoring

Two alditol acetate methods for the gas chromatographic (GC) analysis of neutral and amino sugars were compared. Following sodium borohydride reduction, one method uses methylimidazole as an acetylation catalyst without prior removal of water or borate salts and the other method uses sodium acetate after removal of borate and water. Depending on the acetylation conditions, muramic acid produced different derivatives. With methylimidazole, reliable derivatization of muramic acid was not possible, although other sugars derivatized reliably. With sodium acetate, all sugars tested were reproducibly derivatized. The utility of the sodium acetate method is shown by the trace GC-mass spectrometric analysis of muramic acid and rhamnose derived from bacterial peptidoglycan-polysaccharide complexes in mammalian tissue.     

The exterior algebra ΛkRn and area minimization

The structure of the exterior algebra Λ^kRⁿ is studied in low dimensions, and consequences are drawn for k-dimensional area-minimizing surfaces in Rⁿ. For a general form ø∈Λ²R⁴, Section 3 gives explicit formulas for the comass 6ø6 and the face of the Grassmannian exposed by ø. Section 4 classifies the faces of the Grassmannian of the 3-planes in R⁶ and hence the associated geometries of area-minimizing surfaces (there are four types). Section 5 establishes an equality involving the comass norm in low dimension and draws implications on when the Cartesian product of area-minimizing surfaces is area-minimizing. New examples of area-minimizing integral currents with singularities follow.