Abstract: An improved apparatus and method for absorbing solar energy, the apparatus providing a sealed envelope having a transparent upper panel with a solar energy absorbing panel thermally isolated against convective and conductive heat losses by a partial vacuum in the sealed envelope. The transparent panel has an upwardly extending curvilinear surface which increases its strength characteristics against the pressure differential between the ambient and the partial vacuum inside the envelope. Support structure is also provided in conjunction with the apparatus to place the periphery of the transparent panel under constriction to compensate for tensile stresses imposed thereon by the pressure differential. The inside surface of the transparent panel and the absorber panel are selectively coated with an infrared reflective surface to reflect and reduce losses of infrared radiation emitted by the absorber panel.

Abstract: Reconstruction of the three-dimensional fluid velocity vector field in a moving medium from a set of measurements of the acoustic propagation time between a multiplicity of transmitter and receiver locations on a stationary boundary surface. The inversion of the integrals relating the acoustic propagation path to the propagation time measurements is effected by linearization and discrete approximation of the integrals and application of an algebraic reconstruction technique (ART). The result of the process is to obtain the X, Y, and Z components of the fluid velocity vector at every point within a region bounded by a surface containing the acoustic transducers. Since this technique does not require the presence of scattering centers or the optical transparency of the medium, it may be applied in many cases (i.e., turbid, opaque, or chemically pure media) where Doppler or optical (e.g., laser holography) methods fail.

Abstract: Pulses of acoustic energy are transmitted from a plurality of different directions through a plane of interest, or a number of adjacent planes of interest, of a body to be examined. The body may be biological or non-biological. Time-of-flight of the pulses is measured for individual paths through the body, and from the data thus obtained the spatial distribution of the acoustic velocity through the plane or planes within the body is reconstructed using a mathematical reconstruction technique. The velocity values thus obtained, which are uniquely determinative of the acoustic index of refraction at each point, have diagnostic value, and they can further be displayed by means of a cathode ray tube or other imaging device to provide an image of the internal structure along each plane. The disclosed technique has the advantage of being highly independent of acoustic attenuation and reflections occurring along the paths.