Abstract: End-capping an aromatic diamine or a precursor formed by reaction of an aromatic diamine with an aromatic dianhydride with difluoromaleic anhydride yields prepolymers which thermally cure at temperatures from about 150.degree. to about 200.degree. C. to form polymers which display long-term thermal stability at temperatures up to 300.degree. C. and more.

Abstract: A gas laser having a bandwidth which substantially exceeds the normal doppler bandwidth. To this end the lasing beam is made to propagate at an angle to the direction of flow of the stream of lasing gases. The gases should move at a supersonic speed so that the normal doppler bandwidth of the laser is shifted up or down in frequency by a predetermined amount. By utilizing two or more gas flows at different angles to each other, the normal amplification band of the laser medium can be shifted up and down in frequency by different amounts to obtain an overall bandwidth on the order of 1 - 2 gigahertz (ghz).

Abstract: Various antenna systems are disclosed which generate a shaped beam having a substantially Gaussian distribution substantially without sidelobes. The antenna system consists of basic subarrays consisting of seven or nine radiating elements arranged respectively in a circle with a central element or in the form of a square. The radiating elements are fed in phase but the power applied to each element and the spacing is so selected that due to interference the sidelobes substantially disappear. More complex antenna arrays to form different beam shapes may be formed from the two basic subarrays.