Abstract: A blade assembly for a walk-behind trencher is described. The trencher includes a restraining bar which is affixed to the roller boom and which extends horizontally over the roller boom/digging chain assembly. When rotation of the digging chain is disengaged and the roller boom digger, including the retraining bar, is placed essentially horizontal position, the front end of the backfill blade assembly is mounted on the restraining bar and the rear end of the backfill blade assembly is releasably affixed to the side of the trencher. The trencher itself, after digging a trench, can raise the roller boom to which the restraining bar is attached to a horizontal position, the backfill blade assembly can be quickly installed and the trencher can then be positioned so as to drive over the trench pushing dirt from the side of the trench back into it. A stabilizing bar is longitudinally adjustable so that the backfill blade assembly can be used with differing roller boom lengths.

Abstract: A frequency selective surface devise is described. The device separates or combines two channels by using two or three spaced layers of resonant elements which may be loops or tripoles and which are coupled and which have interactive effects between layers such that the relatively broad transmission and reflection bands characteristic of resonant elements are modified by reinforcement of multiple reflection between the layers in the manner of a Fabry-Perot etalon effect in order to increase the sharpness of the transition of the transmission and reflection bands and thereby to permit combination or separation of closely spaced channels.

Abstract: A prefabricated outer wall structure with stress rupture resistance comprising a plurality of outer wall elements, each outer wall element comprising a wall component formed of an inner unit and a plurality of fixing components, in which the inner unit has a ladder slot and its outer surface is adhered to an outer decorative wall unit by means of adhesive in a manner that at least a retention slot is defined between the ladder slot and the outer decorative wall unit with an U-plate is placed within the retention slot; and each fixing component is connected to at least a hook plate corresponding to the U-plate in the wall component, while an end of the fixing component is secured to a construction structure so that the wall component is tightly secured to the construction structure.