Cubic distortion product otoacoustic emissions in young and aged chinchillas exposed to low-frequency noise.

The aim of this study was to examine susceptibility to noise-induced hearing loss in animals with and without age-related hearing loss (AHL), using cubic distortion product otoacoustic emissions (CDPs) to assess the functional status of the outer hair cell (OHC) system. Subjects were young (< or = 3-yr-old) and aged (10- to 15-yr-old) chinchillas. CDP thresholds and input/output (I/O) functions were measured before and after exposure to 95 dB or 106 dB SPL low-frequency noise. The results indicate that (a) aging in the chinchilla is associated with significant elevations of CDP thresholds and depression of CDP I/O functions, (b) noise exposures cause equivalent CDP threshold elevations and amplitude reductions in young animals with normal hearing and older animals with AHL, and (c) CDP threshold and amplitude measures provide information that complements evoked potentials measured from the auditory midbrain.     

Intense sounds may alter the mechanical properties of the cochlear partition

Morphological and structural changes have been observed in various cochlear elements following exposure to intense sounds. Whether these changes are sufficient to locally alter the mechanical properties of the cochlear partition is unknown. Here a psychophysical test for mechanical changes in the partition is developed and applied. Monaural exposures to an intense 1700-Hz tone were preceded and followed by a binaural task in which the subject adjusted the interaural time difference of a 250-Hz tone in order to perceive it as centered inside his head. If the local gradients of mass, stiffness, and/or coupling were altered by the exposure, then the post-exposure settings should contain a time lead toward one ear or the other, depending upon the direction of the mechanical changes. Following exposure to an intense tone, the maximum temporary threshold shift (TTS) is often displaced upward in frequency from the exposure stimulus--an effect widely known as the half-octave shift in TTS. Time leads toward the nonexposed ear in the post-exposure centering task would be in accord with a mechanical-change explanation of the half-octave shift. Settings in this direction were observed with the most intense and longest durations of exposure used, but with less intense or shorter exposures, the post-exposure settings were initially toward the exposed ear. Thus, the psychophysical evidence reported here supports the idea that exposure to intense sounds does produce temporary, local changes in cochlear mechanics, but it fails to provide a simple confirmation of the possibility that these mechanical changes underlie the half-octave shift in TTS.     

The turbulent Alfvénic aurora

It is demonstrated from observations that the Alfvénic aurora may be powered by a turbulent cascade transverse to the geomagnetic field from large MHD scales to small Alfvén wave scales of several electron skin depths and less. We show that the energy transport through the cascade is sufficient to drive the observed acceleration of electrons from near-Earth space to form the aurora. We find that regions of Alfvén wave dissipation, and particle acceleration, are localized or intermittent and embedded within a near-homogeneous background of large-scale MHD structures.     

Anisotropy of Interfaces in an Ordered HCP Binary Alloy

A multiple-order-parameter mean-field theory of ordering on a binary hexagonal- close-packed (HCP) crystal structure is developed, and adapted to provide a continuum formulation that incorporates the underlying symmetries of the HCP crystal in both the bulk and gradient energy terms of the free energy. The work is an extension of the previous treatment by Braun et al. [Phil. Trans. Roy. Soc. Lond. A 355:1787 (1997)] of order–disorder transitions on a face-centered-cubic crystal (FCC) lattice. The theory is used to compute the orientation dependence of the structure and energy of interphase and antiphase boundaries in ordering to the Cd₃Mg and CdMg structures, which are the HCP analogs of Cu₃Au and CuAu structures in FCC. As in the corresponding FCC case, the multiple order parameters do not form a vector. Anisotropy is a natural consequence of the underlying crystal symmetries and the multiple-order-parameter continuum formation presented here. The isotropy transverse to the sixfold axis expected for a scalar order parameter is not found.     

The catalytic enantioselective, protecting group-free total synthesis of (+)-dichroanone

Herein we report the first enantioselective total synthesis of (+)-dichroanone, confirming the absolute configuration of the natural product. This protecting group-free route features the first application of our enantioselective Tsuji allylation in the context of a natural product total synthesis. Additionally, this 11-step preparation of the molecule from commercial material features a novel Kumada-aromatization strategy and a rapid sequence for the conversion of a phenol to a hydroxy-p-benzoquinone.     

The vibration produced by multiple point defects in a rolling element bearing

A model for the high-frequency vibration produced by a single point defect on the inner race of a rolling element bearing under radial load is extended to describe the vibration produced by multiple points defects. The model incorporates the effects of bearing geometry, speed, load distribution, transfer function and the decay of vibration. A comparison of predicted and measured spectra for a bearing with two point defects confirms satisfactory performance of the model.     

Frequency patterns of TTS for different exposure intensities

Temporary threshold shift (TTS) was measured for several different test frequencies following exposure to a 2500-Hz tone. The intensity of the exposure tone was varied from 82 to 97 dB SPL; its duration was 5 or 10 min. In each post-exposure session, TTS was followed for four test frequencies using a method of adjustment. In all cases, the "center of balance" of the TTS pattern moved upward in frequency as exposure intensity increased. This outcome is consistent with the idea of a basalward migration of the traveling-wave envelope with increasing exposure intensity, but the evidence is not unequivocal.