Abstract: The material silicon carbide possesses not just extraordinarily good thermal, chemical and mechanical properties, as a result of an adjustable porosity it is also possible to apply the material in conditions with difficult tribological relationships. As the porosity influences not only the friction between two workpieces, but also the rigidity of a material, a careful selection of pore diameter, number of pores per unit volume of material and the distribution of the pores in the material is necessary. According to the invention, with a porosity of the sintered silicon carbide body of 2 to 12 vol. %, comprised of non-communicating closed pores, evenly distributed in the material, the pores are spherical and have a nominal diameter of from 10 ?m to 48 ?m.

Abstract: In the permeable structure, which is built up of sheets, continuous channels are arranged in rows and between the rows of channels are formed flow spaces which at opposite sides are bounded bit cover plates. In the flow spaces (4) at least two successive transverse bridges (6) are arranged on the same level, the transverse bridges (6) in at least half of the sheets having a different length (B) and the channels (1) extending essentially perpendicular to the flow spaces (4).

Abstract: In the heat exchanger module, produced by stacking sheet cards provided with openings and subsequently joining the individual cards of the card stack, each sheet card (2) or group of sheet cards of the stack is arranged rotated about a common axis by an angle .alpha. of between 0.degree. and 30.degree. with respect to the preceding sheet card (2) or group of sheet cards, the openings (3) forming helical channels (4).

Abstract: In the board of ceramic material for the construction of permeable structures, the board has three rows of holes which extend parallel to one another and are arranged symmetrically to the axis of symmetry. Three recesses of differing length are arranged between the rows of holes. The recesses intersect the board edge, the longest and one of the two shorter ones opening out at the same board edge and the shortest being opposite the second longest. The webs remaining between the recesses or the recess and the board edge have a length of 25%.+-.0 to 6% in relation to the length of the board determined by the direction of the rows of holes. The boards are stacked in succession to form various layers of the plate heat exchanger as the holes of the stacked boards form continuous channels and the recesses form shallow channels which extend substantially transversely to the continuous channels.

Abstract: A pair of cylinders is rotated in synchronism; each cylinder has a mark on its periphery and the marks are to be moved to angular coincidence. A train of counting pulses is derived from a train of timing pulses which controls the drive of one of the cylinders; when a signal is generated as the mark of this cylinder passes a fixed point, this counting pulse train is applied to a forward-reverse counter to make it count backwards from a reference value. As soon as the signal indicative of the passage of the mark on the other cylinder is generated, the counting pulse train is cut off and a pulse train derived from it but of stepped-down pulse frequency, is applied to the counter to make the same count forward to the reference value. During the forward counting, and until the reference value is reached again, the train of counting pulses is modified by adding or suppressing timing pulses, until the next signals from the one and the other cylinder indicate angular coincidence of the marks.

Abstract: A chess game is provided having a hexagonal board having alternate sides constituting bases for respective of three participants. Polygonal fields are provided on the board in the form of triangles, quadrilaterals or hexagons. These fields extend between the three bases and occupy at least substantially all of the board. Three like sets of men correspond to the bases, and include a king, queen, two bishops, two castles, two knights, a plurality of pawns and a cardinal, which is still movable after the corresponding king is checkmated. There may be provided an extra pawn in each set, and there may also be provided an identifying field or ring to place under or encircle a checkmated king. The cardinal and queen are entitled to similar moves. The cardinal may not conquer men from sets of other participants. The cardinal has social-political characteristics, and it is arranged that this man can be conquered only under difficult circumstances or not at all.