Abstract: An optical module includes a mounting board, an optical element, an optical fiber having an optical axis, the optical fiber inserted in the mounting board to align the optical axis with the optical element, and a positioning mark provided to position the optical element on the mounting board. The mounting board has a groove provided in the middle of the mounting board and extending in a direction of the optical axis of the optical fiber, the groove enclosing the optical fiber when inserted. The groove has a vertical wall which is perpendicular to the direction of the optical axis and confronts a leading edge of the optical fiber when inserted. The positioning mark is located adjacent to an internal edge of the groove where the vertical wall is provided on the mounting board.

Abstract: An optical module includes a mounting board, an optical element, an optical fiber having an optical axis, the optical fiber inserted in the mounting board to align the optical axis with the optical element, and a positioning mark provided to position the optical element on the mounting board. The mounting board has a groove provided in the middle of the mounting board and extending in a direction of the optical axis of the optical fiber, the groove enclosing the optical fiber when inserted. The groove has a vertical wall which is perpendicular to the direction of the optical axis and confronts a leading edge of the optical fiber when inserted. The positioning mark is located adjacent to an internal edge of the groove where the vertical wall is provided on the mounting board.

Abstract: cDNA clones containing the entire genome of Japanese encephalitis virus (JEV) were used to produce infectious, recombinant JEV particles with diverse virulence properties. Certain viruses retained the immunogenicity of JEV, but lacked the ability to cause encephalitis. The mutation associated with this loss of neurovirulence was localized to a nucleotide substitution in the codon encoding the 138th amino acid of the envelop protein, resulting in a mutation of an acidic amino acid to a basic amino acid. Attenuated viruses containing this mutation form the basis of a greatly improved, molecularly defined vaccine for the prevention of Japanese encephalitis in humans.

Abstract: A wavelength stabilized light source includes a laser diode which emits a laser beam of a wavelength of 1.56 .mu.m. A second-harmonic generator generates a second-harmonic light of the laser beam. The second-harmonic light enters a resonator which includes a resonance cell in which .sup.87 Rb atoms are filled. A phase-modulated microwave is irradiated on said resonator. The reasonator outputs a double resonance signal when the wavelength of the second-harmonic light is equal to a resonance wavelength of .sup.87 Rb and the frequency of the microwave is equal to a transition frequency of .sup.87 Rb. A first control circuit controls the microwave so that the frequency of the microwave is equal to the transition frequency. A second control circuit controls the laser diode so that the wavelength of the second-harmonic light is equal to the resonance wavelength of .sup.87 Rb. Thereby, the wavelength of the emitted laser beam is stabilized at 1.56 .mu.m.

Abstract: A cesium oscillator includes a cesium beam tube, and an oscillator circuit which generates an oscillation signal of a frequency to be supplied to the cesium beam tube. A frequency control circuit including a sweep circuit and a feedback loop circuit continuously varies the frequency of the oscillation signal. The frequency of the oscillation signal is continuously varied two times when the frequency of the oscillation signal is to be adjusted. A hold circuit holds the highest signal level of the resonance signal supplied from the cesium beam tube when the frequency control circuit continuously varies the frequency of the oscillation signal first. A control circuit controls the frequency control circuit so as to stop continuously varying the frequency when a signal level of the resonance signal obtained by continuously varying the frequency of the oscillation signal by the frequency control circuit for the second time becomes equal to the highest signal level held by the hold circuit.

Abstract: A method for detecting and determining a volatile or volatilizable substance in an aqueous solution or liquid and an apparatus employed for this method are disclosed. The volatile component, vaporized from the solution through a water repellent and gas permeable membrane, is brought into contact with a dried or partially dried transparent film-like color developing carrier which is provided adjacent to the membrane, and the determination is carried out by the degree of color-change of the carrier. The apparatus comprises a cover plate with sample holes, a membrane, a color developing carrier, and a cover plate with observation windows. The members are fitted tightly together to form a single composite layer.