Performance analysis of a simple roof cooling system with irrigated soil and two shading alternatives

The use of passive cooling on roofs holds a significant unfulfilled potential in hot-arid regions. In this study, the contribution of a watered soil with two types of shading for roof cooling was assessed. Two test cells of approximately 4 m² in area and 2.5 m high were monitored during the summer season. Both cells were covered with a 16-cm layer of soil. One was untreated while the other was watered and shaded consecutively by means of an overhead shading mesh and a layer of lightweight gravel. Temperature profiles were measured across the section of each roof, from the top surface of the soil to the ceiling inside the chamber, and embedded heat flux plates were also used to evaluate the cooling effect. A comparison of the two shading strategies demonstrated that while the mesh provided more cooling over a daily cycle, the daytime cooling potential, which is crucial in a desert climate, was higher with lightweight gravel.     

Optimally isotropic Laplacian operator

Laplacian operators used in the literature for digital image processing are not rotationally invariant. We examine the anisotropy of 3x3 Laplacian operators for images quantized in square pixels, and find the operator which has the minimum overall anisotropy.     

Digital straight lines and convexity of digital regions

It is shown that a digital region is convex if and only if every pair of points in the region is connected by a digital straight line segment contained in the region. The midpoint property is shown to be a necessary but not a sufficient condition for the convexity of digital regions. However, it is shown that a digital region is convex if and only if it has the median-point property.     

Relaxation: evaluation and applications

Probabilistic relaxation labeling processes are iterative parallel schemes that use contextual information to reduce local ambiguities. The behavior of these processes can be described by examining the rates of change and entropies of the probability vectors at each iteration. Examples are given comparing three relaxation processes as applied to several basic image analysis tasks.     

The Max Roberts Operator is a Hueckel-Type Edge Detector

Hueckel's edge detector finds the best-fitting ideal step edge to a given picture neighborhood by expanding the neighborhood and step edge in terms of a set of nine basis functions. A very simple case of this approach uses a 2 × 2 neighborhood and three basis functions. This case is solved explicitly using elementary methods. The magnitude of the best-fitting step edge for the neighborhood AB CD turns out to be the Roberts operator max (|A - D|, |B - C|).     

Blob detection by relaxation

A blob is a compact region lighter (or darker) than its background surrounded by a smoothly curved edge. Blobs can be detected using cooperating relaxation processes to enhance their interior and edge probabilities. A discussion of the processes working independently and together is given. The use of a pyramidal relaxation structure, the use of the closedness of contours as an additional information source, and the extension of cooperating relaxation processes to a time sequence of images are also discussed.     

High frequency performance of Si/sub 1-x/Ge/sub x//Si/sub 1-y/Ge/sub y//Si/sub 1-x/Ge/sub x/ HBTs

The results of a theoretical study of the performance of high speed SiGe HBTs is presented. The study includes a group of SiGe HBTs in which the Ge concentration in the base is 20% higher than that in the emitter and collector (i.e. y=x+0.2). It is shown that the composition dependences of f/sub T/ and the F/sub max/ are non-monotonic. As the Ge composition in the emitter and collector layers is increased, f/sub T/ and f/sub max/ first decrease, then remain constant and finally increase to attain their highest values.<>