This paper describes the results of measurement of noise levels inside subway cars in eleven cities, namely, Berlin, Copenhagen, Hamburg, London, Madrid, Paris, Rome, New York, Nagoya, Osaka and Tokyo. A noise meter made by Rion Co. (Type NA-02) was used. All data were taken with the C weighting networks, in dB RE O. 0002 microbar. It was comfortable inside the subway cars in Paris (No. I Line), Berlin (a new car), and Tokyo (Hibiya Line), in which sound pressure was on a level of less than 85dB, and measured values averaged about 80dB.
Temperature Dependence of Complex Young's moduli of different practical polymer materials has been measured at the frequency of tens of cps and in the temperature range of -30 +l00°c. `Mean temperature coeffcients' of complex Young's moduli in the neighborhood of room temperature are tabulated. Temperature dependence of resonance frequency and specific response at low frequencies of the plastic diaphragms of stiffness control is discussed as an example. Interrelations between loss tangent and storage modulus or its temperature coefficients are studied in detail. It is shown that apparent activation energy of relaxation time of thermorheologically simple materials can be obtained approximately from the measurement of the ratio of loss tangent to temperature coefficients of storage modulus.
The underwater sounds from the boat driven by hydrojet were compared with those from boats driven by propeller in order to verify whether the hydrojet propulsion system is acoustically suitable for fishing boats. A measurement of underwater and airborne sounds was made in Negishi Bay, Kanagawa Prefecture. It was observed that the overall sound level in the water from the hydrojet boat was about 20 dB lower than that from the propeller boat at an engine speed of 3, 000 rpm and the spectra of the hydrojet boat had little energy at higher frequencies than 1, 000cps in contrast to the spectra of the propeller boat. Considering the experimental results and studies on the auditory sense of fish which are reported in several literature, the hydrojet propulsion system will be acoustically advantageous to fishing boats, although the problem of the difference of the underwater sound between the tested boat and fishing boats in practical service remains to be solved. This propulsion system may be effective when low underwater sound levels are required.
Optical systems have the properties that a relation of Fourier transform exists between the light wave amplitude distributions at the front and back focal planes of a lens of the system and that at the same time multiplication is performed by a simple imaging process, namely by making the first transparency imaged on the second. This paper presents the method of realization, the operational principles and theoretical considerations of the optical correlator which consists of two ultrasonic light modulators and three lenses, taking advantage of the light diffraction by traveling ultrasonic waves and the optical properties described above. Some experimental results are also presented.