A datacenter or server farm having servers mounted to blow air at an angle in a hot aisle. The greeting cards have a partially hollowed foam body or one or more cavities in the foam body concealed in the front and back by the planar sheet material which may be pre-cut in the shape of the foam body are decorated consistent with the design of the foam body. The measuring devices have output signals which are suitable as regulating variables for the orientation of the directions on the interaction point, and actuating elements are provided for adjusting and tracking at least one of the directions of either the target jet or the energy beam depending on the output signal of the measuring devices in the manner of a control loop. Moreover, for each packet-optical transport device, the controller controls assignment of individual wavelengths within each channel group so as to balance channel utilization around a center of the spectral range associated with each channel group and to maintain spectral separation of the channels within the channel group. Examples of fluid machinery applications include: wind turbine, water turbine or propulsion turbine arrangements.