Formal opticianry training is offered in community colleges and a few colleges and universities. In 1993, there were about 40 programs. Of these, 23 were accredited by the Commission on Opticianry Accreditation and awarded 2-year associate degrees in ophthalmic dispensing or optometric technology.
A teething ring, for use by a child, comprising an outer ring, an inner hub, and spokes radially connecting the outer ring and inner hub. The outer ring is made of a material suitable for aiding a teething child such as a semi-hard rubber or plastic, and is selectively dipped in a material most suitable...
Piston rings for engines with relatively low to medium piston speeds are generally made from cast iron. The rather brittle nature of cast iron is the reason why rings sometimes break under stress. If piston rings are made of steel this will not occur-eg many modern engines now use exotic materials.As speeds rise rings become thinner and have to work a lot harder, so manufacturers move to more durable materials which are outside of the scope of this article.f piston rings are made of steel this will not occur-eg many modern engines now use exotic materials. As speeds rise rings become thinner and have to work a lot harder, so manufacturers move to more durable materials which are outside of the scope of this article.