tailieunhanh - Acoustic Waves From Microdevices to Helioseismology Part 8

Tham khảo tài liệu 'acoustic waves from microdevices to helioseismology part 8', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 268 Acoustic Waves - From Microdevices to Helioseismology In order to unify CM measurements two distinctive and universal measurement points were established the cochlea s apex for the frequencies of 260 500 1000 and 2000 Hz and the cochlea s base for 4000 and 8000 Hz. Phase in each measuring point is related to phase on apex at 60 dB. Influence of whole-body vibration on inner ear Vibration is one of the most widespread injurious factors in the environment of civilized man Palmer et al. 2000a 2000b . The energy absorbed can have a pathological effect on all the tissues and organs of the body although the consequences of exposure to vibration do not present a uniform clinical picture Jones 1996 Seidel Heide 1986 . Because all machines and vibration devices also produce noise usually the combined effect of the two factors is examined Castelo Branco 1999 . There is a prevalent view that mechanical vibrations exert only a weak additionally traumatic influence on the hearing organ Seidel 1993 . Several experimental investigations into the harmfulness of vibration were carried out on animals Hamernik et al. 1980 1981 . Changes in the hearing organ most often would be found in the hair cells Rogowski 1987 . This made us undertake our own research in the 1990s. In order to determine the impact of long-term general vibration on the inner ear it was necessary to 1 design and built noiseless vibration apparatus 2 subject several groups of animals to general vibration defined by controlled parameters over different periods of time and 3 evaluate selected parts of the organ of hearing using norms based on values derived from a control group. In order to ensure proper experimental conditions . sinusoidal 10 Hz vertical 5 mm shaking a device consisting of an electric impulse generator a power amplifier and an impulse exciter was built fig. 9 . Experiments were carried out on young coloured guinea pigs of both sexes weighing 240-360g. Fifty six animals with the normal .