The individual feathers in the skin of a developing chicken embryo are arranged in a precise array within a series of so-called 'tracts'. The images above show nascent feather buds in the legs of embryos at 8–9 days of incubation. Buds are added sequentially across the forming feather tract, as shown by the range of developmental stages in the image at top left. (In all three upper images, buds...

at the boundary between jurassic and cretaceous, because of late kimmerian movements, the sea ragressed from many areas of north and cantral iran, and many continental areas rose, which included a number of differentiated basins. the boundary between jurassic and cretaceous in these parts of iran is usually marked by a big diastem or by red, clastic and evaporitic sediments. the whole or part o...

This paper treats the problem of the merging of formations, where the underlying model of a formation is graphical. We first analyze the rigidity and persistence of metaformations, which are formations obtained by connecting several rigid or persistent formations. Persistence is a generalization to directed graphs of the undirected notion of rigidity. In the context of moving autonomous agent f...

Multi-agent formations have been recently the subject of many studies. An important operational challenge, largely unaddressed in the literature, is to ensure that functionality of the formation is retained should agents be lost through misadventure, mission reassignment, and so on. In the context of sensor networks, it is also important to allow for the loss of multiple sensors as the low qual...

Marine transgressions or microbial precipitation: What was the controlling factor of continental margin iron formation deposition? Introduction Iron formations, which can be found around the world today, have great importance as sources of iron and manganese ore, clues about the evolution of life on Earth, and even hints at possible life on Mars (Weber et al., 2006). Precambrian iron formations...

SUMMARY Low permeability, high retention capacity and self-sealing ability are advantageous characteristics that attributed to argillaceous rocks. In contrast, other properties of clay, such as internal heterogeneities, strong attenuation anisotropic behaviour, pose major challenges for underground exploration techniques. Although with regard the storage nuclear waste, seismic in itself is grea...