排序方式: 共有2条查询结果,搜索用时 0 毫秒
1
1.
V.M. Luboshits 《Geophysical Journal International》1987,91(2):349-354
Summary. It is shown that at any orientation of a dipole of direct current at the surface of a uniform anisotropic halfspace there exists a unique critical value ηcr of the "vertical" electric anisotropy η. For η > ηcr not all field lines are closed, and three straight field lines pass through the centre of the dipole. Also there exists a unique value ηeq > ηcr , where equatorial η is equal to zero. If η > ηeq then equatorial ρapp is negative since the electric vector is turned more than through 90° at the equator of dipole, and it is shown that ηcr = 1.79, ηeq = 1.93 if the axis of dipole is directed symmetrically with respect to the axes of anisotropy. Routine observations of variations of ρapp with the aim of earthquake prediction should be carried out taking into account the possibility of great fluctuations on η far from the epicentre of an earthquake. 相似文献
2.
F Otero-Ferrer R Herrera VM Tuset J Socorro L Molina 《African Journal of Marine Science》2015,37(3):395-404
This study represents the first report on seahorses in the Macaronesian islands (North-East Atlantic), determining the spatial and seasonal abundance, population structure and physical appearance of European short-snouted seahorse Hippocampus hippocampus. Animals were surveyed off Gran Canaria Island in two bays, Melenara and Sardina del Norte, within three habitats: rocky bottom, artificial substrata and seagrass. Populations were monitored over a 5-year period (spring 2006–winter 2011) using 15-minute visual fast count (VFC) surveys. Seahorses were characterised by low abundances, small proportions of subadults and roughly equal sex ratios at each site. We aimed to determine whether environmental conditions and geographical position could explain differences in seahorse abundance and population structure between the study sites. Melenara Bay (mean sighting rate = 0.44 individuals VFC–1; SD 0.72) offered protected environments where seahorse distribution varied with substratum type, irrespective of season. Strong hydrodynamic forces in winter affected abundance and size at exposed locations in Sardina del Norte Bay (mean sighting rate=0.21 individuals VFC?1; SD 0.52). Our findings contribute to the scarce available knowledge about this Data Deficient species (IUCN Red List), helping to establish future conservation strategies and management recommendations for the preservation of H. hippocampus populations around Gran Canaria Island and other localities with similar coastal environments. 相似文献
1