Abstract: The invention provides a data recording/reproducing apparatus for recording and reproducing data on and from a disklike recording medium while rotating the disklike recording medium by a spindle motor having ball bearings. In this apparatus, the ratio of the number of revolutions (the frequency of a minimum-frequency vibration component of a non-repeatable vibration) of each ball in the ball bearings, to the number of rotations (the rotational frequency) of the spindle motor is substantially set to 1/n, and servo track writing is performed in synchronism with every n rotations of the spindle motor.

Abstract: A resin composition useful as a matrix resin for a composite material comprises (A) from 30-80% by weight of an amino group-containing unsaturated ester compound obtained by ring-opening addition reacting an epoxy group-containing unsaturated compound (c) with an aromatic polyamine (a) or diamine (b) in an equivalent weight ratio of compound (c) to amino hydrogen atom of polyamine (a) or diamine (b) of from 0.25-0.9:1, (B) from 10-60% by weight of a polyepoxy compound, and (C) from 5-60% by weight of a radically polymerizable cross-linking agent such as p-methyl styrene.

Abstract: A heat-resistant resin composition, comprising (A) 30 to 95% by weight of at least oen unsaturated ester compound selected from the group consisting of (I) unsaturated ester compounds represented by the formula I: ##STR1## wherein R.sup.1 s independently stand for one member selected from the class consisting of ##STR2## wherein R.sup.3 and R.sup.4 independently stand for a hydrogen atom or a methyl group, and a hydrogen atom, and at least one R.sup.1 stands for ##STR3## wherein R.sup.3 and R.sup.4 independently stand for a hydrogen atom or a methyl group, and R.sup.2 s independently stand for an atom or an organic group selected from the class consisting of a hydrogen atom, halogen atoms, a methoxy group, and alkyl groups of 1 to 5 carbon atoms, and m stands for 0 or an integer in the range of 1 to 10, and (II) unsaturated ester compounds represented by the formula II; ##STR4## wherein R.sup.5 s independently stand for one member selected from the class consisting of ##STR5## wherein R.sup.3 and R.sup.