Comodulation detection differences using noise-band signals

In a variant of the standard paradigm employed to study comodulation masking release (CMR), a narrow noise band was used as a signal in the presence of "cue" bands which had either the same or different temporal envelopes. The number of cue bands present ranged from zero to four; when there were two or four cue bands, they were either all presented at the same overall level or the spectral profile was "scrambled" in a haphazard manner. Different noise samples were presented within and across trials. The result was in the opposite direction from the standard CMR outcome; that is, better performance was obtained when the envelopes of the cue band(s) were uncorrelated with those of the signal band than when they were correlated. These comodulation detection differences (CDDs) ranged from a decibel or two up to 10-12 dB in different conditions, and were generally larger the more cue bands present. Standard CMR conditions, which were run as controls, revealed that the detectability of a tonal signal does not increase as the number of cue bands is increased from one to four-an outcome which differs from those obtained in profile analysis experiments. The data taken with the equal-level and the scrambled-level cues differed little in both the CDD and the CMR conditions. All noise bands were 100 Hz wide, and approximately 250 ms in duration. The signal band in CDD and the masker band in CMR were centered at 2500 Hz. The psychophysical procedure was two-interval forced choice.     

Vibrational modes and infrared absorption of interstitial oxygen in silicon

A quasi-linear Si₂O molecule model (QLMM) is suggested from an analysis of the configuration and the interactions of an isolated oxygen atom with its neighbor silicon atoms. The vibrational modes are assigned and the infrared absorption spectra are calculated in detail with the model. The theoretical results are in reasonably good agreement with reported experimental values. This agreement shows that for the analysis of the vibrational modes of the interstitial oxygen atom in silicon crystals it is not necessary to consider the coupling of the molecule with the rest of the lattice. The interaction of the oxygen atom with its six second-nearest silicon atoms only causes the level separation of the ₂ mode and the formation of the fine structure.     

Many-body effects in nuclei

A correction to nuclear structure calculations due to the finite lifetime of the excited states of a nucleus entails many-body effects of different nature. The analytical structure, as well as the results of numerical calculations, are given and discussed.Presented at the symposium Mesons and Light Nuclei, Bechyn, Czechoslovakia, May 27–June 1, 1985.     

On the multiplicative group generated by a dense sequence of integers

The subgroup of the positive rationals, generated by a sequence of upper density , has index essentially not exceeding ^–1.In honor of the seventieth birthday of Professor E. HlawkaPartially supported by N.S.F. Contract No. DMS-8500949.     

A two-stage nonlinear cochlear model possesses automatic gain control

A model of the cochlea is explored using as stimuli two simultaneously presented sinusoids of equal amplitude. The model consists of two stages: a linear bandpass filter, followed by a reservoir-type representation of the hair-cell/nerve-fiber complex. Fast Fourier transforms of the model's output were computed. While the amplitudes of the individual response components were strongly nonlinear functions of intensity, the ratio of the magnitudes of the response components at the frequencies of the two stimulating sinusoids was found to be nearly equal, over a wide intensity range, to the ratio of the amplitudes which those stimulating sinusoids possessed at the output of the filter. Thus the reservoir stage exerts "automatic gain control".     

Confusion effects with sinusoidal and narrow-band noise forward maskers

In some forward-masking conditions, signal thresholds may be elevated by the listener's inability to distinguish the signal from the preceding masker. In this study, such "confusion" effects are investigated for both sinusoidal and narrow-band noise forward maskers combined with sinusoidal signals of varying duration. Results for the sinusoidal maskers show effects of off-frequency listening for brief signals and possibly small effects of confusion for longer signals. Results for the narrow-band noise maskers show a marked influence of confusion over a wide range of signal durations. This range is in good agreement with that predicted from previous work with "pulsing" maskers [D. Neff, J. Acoust. Soc. Am. 78, 1966-1976 (1985)]. These results suggest that studies using narrow-band noise forward maskers or studies of psychophysical suppression should include direct tests for confusion effects in key conditions.     

Al2O3-supported Fe?Ni catalysts for CO hydrogenation, I. Catalytic properties

CO conversion to hydrocarbons at various reaction temperatures and atmospheric pressure has been investigated on alumina-supported Fe, Ni and Fe–Ni catalysts. Maxima of activity and selectivity were obtained in hydrocarbon formation as a function of Fe content in the samples, which corresponds to a certain stoichiometry of metallic components.     

Effect of the atomic number of the support on space-charge buildup in electron-irradiated dielectric films

A study is made of the effect of the atomic number z_s of the support on the charging of thin dielectric films irradiated with 50-keV electrons at beam densities of 10^–5–10^–4 A·m². It is shown that at larger z_s the ratio between the charge-injection and pair-production rate increases, producing a higher space-charge buildup efficiency. The maximum charge increases with the current density, while is not affected. It is found that the charging process is associated with a spacecharge current.Translated from Izvestiya Vysshikh Uchebnkh Zavedenii, Fizika, pp. 14–18, No. 1, January, 1986.     

Vacuum polarization by a Coulomb center and strong magnetic field. modification of Coulomb's law

The proper time method is used to examine the effect of polarization of the electron-positron vacuum on the nature of the interaction of a charged particle with the field of a nucleus and a magnetic field. It is shown that the interaction of an electron with a nucleus becomes anisotropic in the presence of a magnetic field. The dielectric constants of the vacuum and the effective charge of the Coulomb center are calculated.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 38–45, November, 1986.