Calculations of Mott elastic scattering cross section of electrons for most elements of the periodic table up to element number 94 in the energy range 20 eV–20 keV have been performed. The Dirac equation transformed to a first-order differential equation was solved numerically. The influence of the choice of atomic potential on the scattering factor was studied in comparison to a simple muffin-tin approximation of the atomic potential in solids. The application of calculated cross sections to a conventional Monte Carlo model for electron scattering using modified Bethe equation is described and results concerning the electron backscattering for different atomic potentials are compared.

Empirical forms have been found for the total and differential elastic scattering cross sections for electron/atom scattering. The cross sections are valid over the range 0.1–30 keV and across the periodic table. The empirical forms of the cross sections are derived from trends in tabulated Mott scattering cross sections. The form of the total cross section is similar to a previously published cross section and is based on the screened Rutherford cross section. The fit to the differential Mott cross sections is decomposed into two parts, one part being of the same mathematical form as the screened Rutherford cross section σR, and the second part being an isotropic distribution σI. These two mathematical forms were chosen because they give a straightforward generation of random scattering angles. The screened Rutherford part of the differential scattering cross section is first fitted to the half-angle of the Mott cross sections. This fit of the differential screened Rutherford is in turn reduced to a fit of the screening parameter alone over energy and atomic number. The screened Rutherford part of the cross section is highly peaked in the forward scattering direction and needs to be balanced by the isotropic distribution. The ratio of the total cross sections (σR/σI) between the screened Rutherford part of the differential scattering cross section and the isotropic part of the distribution is then fitted to give the same ratio of forward to backscattered currents as the tabulated Mott differential cross sections. Using this dual form of the scattering cross section for the differential cross section, and the previously (independently) fitted total cross section, the backscattering coefficients for normal incidence are calculated. The two equations describing the differential cross section, one for the Rutherford screening parameter and one for the ratio σR/σI, are simplified to remove redundant parameters, and then fitted to the backscattering coefficients calculated directly from the tabulated Mott cross sections. A straightforward expression for the differential cross section was found to give backscattering results covering all the major trends with energy and atomic number compared to the backscattering coefficients calculated using tabulated Mott cross sections.

Vowel identification was tested in quiet, noise, and reverberation with 20 normal-hearing subjects and 20 hearing-impaired subjects. Stimuli were 15 English vowels spoken in a /b-t/context by six male talkers. Each talker produced five tokens of each vowel. In quiet, all stimuli were identified by two judges as the intended targets. The stimuli were degraded by reverberation or speech-spectrum noise. Vowel identification scores depended upon talker, listening condition, and subject type. The relationship between identification errors and spectral details of the vowels is discussed.

Empirical forms for electron/atom scattering cross sections predict backscattering factors that compare well with those calculated using tabulated Mott data from 0. 1 to 30keV. The form of the empirical total cross section is similar to the screened Rutherford cross section. The fit to the tabulated differential Mott cross sections is decomposed into two parts, one part being of the same mathematical form as the screened Rutherford cross section (0R), and the second part being an isotropic distribution (ao). The ratio of the total cross sections (oR/Oj) between the screened Rutherford part of the differential scattering cross section and the isotropic part of the distribution, is fitted to give the same ratio of forward to backscattered currents as the tabulated Mott differential cross sections. The three equations, one for the total elastic cross section and two equations describing the differential cross section, one for the Rutherford screening parameter and one for the ratio aR/O,, give backscattering results covering all the major trends with energy and atomic number compared to the backscattering coefficients calculated using tabulated Mott cross sections. However, agreement with experiment is poor for some well 94-26694

The relationship between relative intensity of transition segments and identification of diphthongs has been investigated. In the first experiment, synthesized stimuli were used. The stimuli differed in the amount of attenuation of the transition segment which ranged from 0 to 15 dB. It was expected that [diphthong in text] responses would be obtained for stimuli with attenuated transitions. The stimuli were tested in quiet, noise, and reverberation with ten normal-hearing and seven hearing-impaired subjects. For the stimulus with the most attenuated transition, the normal-hearing subjects gave no [diphthong in text] responses and the hearing-impaired subjects gave only 20% [diphthong in text] responses in quiet. However, in noise, both groups of subjects gave 70% [diphthong in text] responses and in reverberation, the normal-hearing subjects gave 95% and the hearing-impaired subjects gave 90% [diphthong in text] responses. Generally, less transition attenuation was needed for the hearing-impaired than for the normal-hearing subjects to give [diphthong in text] responses. These findings indicated that identification errors in noise and reverberation for naturally produced diphthongs might be related to the intensity of their transition segments. In the second experiment, naturally produced diphthongs [diphthongs in text] from the Nábĕlek et al. [J. Acoust. Soc. Am. 92, 1228-1246 (1992)] study were spectrally analyzed. There were 30 different tokens for each diphthong. The results of the analyses indicated significant correlations between the number of identification errors for these diphthongs made by either normal-hearing or hearing-impaired subjects and the relative intensities of the F2 transition segment. In both noise and reverberation there were fewer errors for the diphthong tokens characterized by high intensity F2 transitions.