An optical emission scheme was demonstrated, in which a high-refractive-index waveguide is excited by a traveling electron beam in a vacuum environment. The waveguide was made of Si-SiO 2 layers. The velocity of light propagating in the waveguide was slowed down to 1/3 of that in free space due to the high refractive index of Si. The light penetrated partly into the vacuum in the form of a surface wave. The electron beam was emitted from an electron gun and propagated along the surface of the waveguide. When the velocity of the electron coincided with that of the light, optical emission was observed. This emission is a type of Cherenkov radiation and is not conventional cathode luminescence from the waveguide materials because Si and SiO 2 are transparent to light at the emitted wavelength. This type of emission was observed in an optical wavelength range from 1.2 to 1.6 m with an electron acceleration voltage of 32-42 kV. The characteristics of the emitted light, such as the polarization direction and the relation between the acceleration voltage of the electron beam and the optical wavelength, coincided well with the theoretical results. The coherent length of an electron wave in the vacuum was confirmed to be equal to the electron spacing, as found by measuring the spectral profile of the emitted light.
It is well known that reconstruction for discontinuity of the ossicular chain , without inflammatory disease, has a good prognosis.Eleven cases of congenital ossicular chain malformation without ossicular fixation and 6 cases of ossicular chain injury due to the head trauma or an earpick, were treated surgically . The method of reconstruction and the prognoses, according to short-term and long-term follow up , were studied in these 17 cases.The following results were obtained:1) In almost all cases, the pure tone audiograms were flat or slightly rising types, and the mean air conductive hearing loss was about 60 dB. Only 2 cases showed the falling type with conductive hearing loss. Connective tissue was observed at the incudo-stapedial joint intraoperatively in these two cases.2) Mean hearing improvement was in 31.8 dB in the low frequency region (125, 250, 500 Hz), 22.7 dB in the middle frequency region (500, 1000, 2000 Hz), and 12.9 dB in the high frequency region (2000, 4000, 8000 Hz), within 3 weeks after operation, in all 17 cases.3) No clear changes in hearing level were seen posteroperatively, for the four periods evaluated; 1-3 weeks, 1-3 months, 4-6 months and over 7 months in all cases.4) The cases in whom the reconstruction was performed between the incus and stapes, especially the foot plate of the stapes, showed poor hearing recovery.5) There was no relation between hearing recovery and the prostheses used in reconstructions.However, it was thought that pieces of the patient's own cartilage or bone should be used whenever possible.
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