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We investigated forward masking in 21 gerbils as a function of age (5-47 months) using 400ms maskers at 40dB SPL and a 20ms, 2.85kHz probe presented 2.5ms after the masker. Elevated thresholds for the unmasked probe were only observed in animals older than 3 years. Unmasked thresholds showed no significant age-dependent hearing loss in animals below 3 years of age. In these animals without peripheral hearing loss, we found a significant age-dependent increase of masker-induced threshold shift. A regression analysis revealed that threshold shift increased from 23dB in 1 year old gerbils to 37dB in 3 year old animals. Increased forward masking in these animals with no sign of peripheral hearing loss points to a central processing deficit.

Age-dependent hearing loss has been well documented in gerbils exceeding 2 years of age using physiological methods (e.g. [Mills et al. (1990) Hear. Res. 46, 201-210]). We determined behavioral thresholds for broad-band noise and pure-tone pulses in gerbils as a function of age. Contrary to expectations based on previously published physiological data, we found no significant (broad-band noise and 10 kHz) or only a very small hearing loss (7 dB at 2 kHz) in 30-36-month-old animals. In animals over 3 years of age we observed an increased spread of thresholds and threshold shifts exceeding 20 dB in some individuals. Behavioral thresholds of old gerbils from two breeding colonies (University of Regensburg and Medical University of South Carolina) were similar. Data from individual animals where thresholds were determined physiologically and behaviorally indicate that results from auditory brainstem response measurements show no shift at 18 months while subsequent measurements at 28-29 months revealed age-dependent threshold shifts of 10-15 dB. In contrast, thresholds determined by behavioral methods in these same individuals at 31-33 months of age remained stable.

Synopsis This paper reviews the status of experiments bearing on the band structure of semiconductors, with particular reference to germanium and silicon. The situation in n-Ge is especially clear, as both cyclotron resonance and magnetoresistance experiments show that the energy surfaces at the bottom of the conduction band are prolate spheroids oriented along the [111] directions in k-space; the spheroids are highly anisotropic, with a mass ratio of about 15:1. In p-Ge the two isotropic lines in cyclotron resonance suggest that the band edge is at the center of the Brillouin zone; the multiplicity is explained by spin-orbit splitting. It appears that this model may account, qualitatively for the remarkable infra-red absorption of p-Ge, but it seems to be difficult to explain transport data. From magnetoresistance and from cyclotron resonance it is found that the energy surfaces in n-Si are prolate spheroids directed along [100] axes, while the structure of p-Si is like p-Ge.

A theory is given that accounts qualitatively for the observations of thin and thick domain walls in ferroelectric and ferroelastic crystals, with special reference to the 90° walls in BaTiO 3 and to the 180° walls in GMO.

The linearized Landau-Ginzburg equation is used to calculate H c3 for a cylindical cavity in a type II material H c3 exhibits oscillations as a function of the cavity radius R when R is if the order of the coherence length. H c3 increase to the Saint-James and De Gennes limit for large R .

An explanation is given for the long time delay in the formation of gamma phase EHD in germanium. The Cerenkov radiation of phonons by moving alpha drops at velocity mach 0.2–0.3 is calculated to be the controlling process in the time delay.

Many realizations of infinitely adaptive crystal structures have been reported recently. It is shown that the elastic energy associated with the forced coherent registration of two types of lattice planes gives a long range repulsive interaction that can account for the observations.

We consider the Kroemer experiments on explosive instabilities in EHD in Ge in the light of an extension of the Altukhov theory to encompass general values of ωτ and of the ratio of drop radius to rf penetration depth. We suggest that the drops were heated above their critical temperature, but by a monotonic path.

If a band edge has N equivalent minima in the Brillouin zone, it is possible consistent with the exclusion principle to place 2 N identical electrons in the same molecular orbital. This theorem suggest the possible stability of exciton molecular complexes, (exc) 8 in Ge and (exc) 12 in Si.