Abstract: The present invention provides a novel liquid crystalline polyester comprising structural units represented by the following general formulae A, B, C and D: ##STR1## where X and Y are each independently H, Cl, Br or an alkyl group having 1 to 4 carbon atoms, the molar ratio of A/B is in the range from 49/1 to 20/30 and that of C/D is in the range from 10/40 to 45/5.

Abstract: In a rear-projection screen comprising a Fresnel lens and a light-diffusing member such as a lenticular lens sheet, a rise angle in a central region of the Fresnel lens is smaller than a rise angle in an intermediate region thereof (e.g., the former is not larger than 3.degree. and the latter is larger than 3.degree. ). The rise angles may preferably gradually increase from the central region of the Fresnel lens toward the intermediate region thereof. The central region of the Fresnel lens may preferably be a region extending within the range of from 1/4 to 1/3 from the middle point of a diagonal of the rear-projection screen. Such a Fresnel lens is effective for improving white uniformity in the intermediate region of the rear-projection screen and eliminating color corn in the central region thereof.

Abstract: A hydraulically actuated tensioner of a toothed belt. A piston slidable with clearance in a cylinder forms front and rear oil-filled chambers communicating through a passage in the piston with a check valve for restricting flow in one direction. A piston rod extending from one end of the piston is urged by a spring, through the front chamber, against a roller to impart tension on the belt. An oil reservoir communicating with the front chamber is enclosed by a spring-biased diaphragm for maintaining the oil pressure in the chambers above atmospheric pressure at all times.

Abstract: Novel 2-oxopyrrolidine compounds represented by the formula ##STR1## wherein R.sup.1 and R.sup.2 are hydrogen or alkyl group, respectively, A is alkylene group or phenyl substituted alkylene group, and B is alkylene group,or a salt thereof, a process for the preparation thereof, and a pharmaceutical agent comprising the compound or salt as an effective component.