Abstract: A method of causing an observer to get an three-dimensional impression of a scene from a two-dimensional representation thereof is disclosed. The observers movements, in particular the movements of his head and/or eyes are monitored and means are provided by which, depending on these movements, two-dimensional representations uniquely associated with each position of the head and/or eyes are displayed on a screen. According to the invention, the display means represent the relative parallactic displacements between all the objects in the scene relative to a predetermined fixation point in the scene.

Abstract: A method for the prevention of arcing in a spark erosion process, in which a pulse-shaped voltage is applied across an electrode and a workpiece, which voltage has a first predetermined value during a variable ignition retarding period determined by the process parameters, and on the termination of this ignition retarding period a discharge takes place between the electrode and the workpiece, resulting in the flow of a pulse-shaped current and in the voltage dropping in absolute sense to a second value determined by the process. The method comprises the additional steps of determining whether the voltage pulse satisfies a predetermined criterion and discontinuing voltage pulses failing to satisfy this criterion.

Abstract: The invention relates to a laminate composed of two, three, four or more aluminum-containing metal sheets. The metal sheets, which may for instance be of an aluminum alloy, are bonded together by means of adhesive layers. In the adhesive layers, which are of a thermohardening material, there are embedded poly-paraphenylene terephthalamide threads. These threads are provided in the form of yarns made up of endless filaments and lie in a practically straight line in the adhesive which substantially consists of a thermohardening material. The adhesive layers contain the threads in an amount of 20 to 80% by weight.

Abstract: The invention relates to a laminate composed of two, three, four or more metal sheets. The metal sheets, which may for instance be of an aluminum alloy, are bonded together by means of adhesive layers. In the adhesive layers there are embedded poly-paraphenylene terephthalamide or carbon threads having a high modulus of elasticity. In the unloaded state of the laminate in its entirety there is a compressive stress in the range of 0 to 200 or 300 N/mm.sup.2 in each metal sheet and a tensile stress in each layer with threads. The material according to the invention is in the first place meant for use in the field of aircraft or spacecraft engineering. However, it also may with advantage find application in various other fields of engineering where high demands are made on static, dynamic fatigue properties and damage tolerance.