One of the fundamental abilities required in autonomous agents is homing. Natural agents—for instance, desert ants—solve the homing problem mainly by using path integration within an egocentric frame of reference. When employing such a mechanism, compass information for determining direction is necessary, and the precision of the compass will have a crucial effect on the precision of homing. For deriving compass information, certain insects use the pattern of polarized light in the sky that arises due to scattering of sunlight in the atmosphere (polarized light compass). The analysis of skylight polarization is mediated by specialized photoreceptors and neurons in the visual system. Inspired by the insect's polarized light compass, we have constructed a polarization compass that was employed successfully on the mobile robot Sahabot. Three models for extracting compass information from the polarization pattern of the sky were tested. In this article, we describe the navigation system and report results of experiments performed with the Sahabot in one of the natural habitats of the desert ant Cataglyphis in North Africa.

Abstract. Simvastatin, a cholesterol synthesis inhibitor, enhances BMP2 expression in osteoblasts. The purpose of the present study was to examine whether simvastatin stimulates bone regeneration when combined with calcium sulfate as a carrier. Critical-sized bone defects in rat calvaria were treated with calcium sulfate or with combination of 1 mg simvastatin and calcium sulfate. In the combination group, although the least amount of bone formation with intense soft tissue inflammation was observed at 2 and 4 weeks, remarkable bone formation was evident at 8 weeks. Conclusively, the combination of simvastatin and calcium sulfate stimulated bone regeneration in spite of the inflammatory response.

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