Abstract: Amorphous silicas having a crystalline appearance, at least two surfaces in symmetric relation, a length of about 1 to about 500.mu. and a thickness of about 50 A to about 1.mu., the length being at least about 10 times the thickness, the amorphous silicas being in the form of primary particles, secondary particles, aqueous dispersions of the particles and shaped bodies.

Abstract: Amorphous silicas having a crystalline appearance, at least two surfaces in symmetric relation, a length of about 1 to about 500.mu. and a thickness of about 50 A to about 1.mu., the length being at least about 10 times the thickness, the amorphous silicas being in the form of primary particles, secondary particles, aqueous dispersions of the particles and shaped bodies.

Abstract: A pickup tube structure comprises an image pickup tube and a yoke assembly mounted on the pickup tube. The yoke assembly includes a magnetic shield in a specific arrangement with respect to the axis of the pickup tube, as well as beam focusing and deflecting coils. The shield is shaped in a cylindrical form with an almost linear joint portion placed in parallel with the tube axis. The angle between the plane including the joint portion and the tube axis and the plane including the direction of the magnetic field for the beam horizontal deflection and the tube axis is not smaller than about -30.degree. and is not larger than about +30.degree..