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61.
62.
Y Qhaji B Jansen van Vuuren I Papadopoulos CD McQuaid 《African Journal of Marine Science》2015,37(3):345-351
The Wild Coast in south-eastern South Africa is strongly influenced by the warm, southward-flowing Agulhas Current. This current has a significant impact on dispersal in the coastal biota of the region, and facilitates high levels of connectivity among populations. However, it is not known how the region's high-velocity hydrology affects genetic population structure in endemic estuarine species, populations of which are frequently isolated from the sea. Here, we compared genetic structure in two estuarine crabs of the family Hymenosomatidae. Both are presumed to have low dispersal potential, but they differ in terms of their life histories. Hymenosoma longicrure has abbreviated larval development and can complete its entire life cycle within estuaries, whereas Neorhynchoplax bovis is a direct developer that lacks planktonic larvae. Using DNA sequence data from the mitochondrial COI gene and the intron of the nuclear ANT gene, we found that levels of genetic structure differ considerably between the species. Depending on the genetic marker used, H. longicrure is genetically homogeneous (COI) or displays low levels of genetic structure and minor evidence of recruitment near natal sites (ANT). In contrast, connectivity in N. bovis is much lower, as this species has a unique combination of alleles at each site, indicating that recruitment is mostly local. These results support previous findings suggesting that even a short larval dispersal phase is sufficient to maintain high levels of connectivity and prevent genetic divergence among populations. 相似文献
63.
D. N. Asimakopoulos C. G. Helmis K. H. Papadopoulos J. A. Kalogiros P. Kassomenos M. Petrakis 《Meteorology and Atmospheric Physics》1999,70(1-2):97-110
Summary According to past experience, the nearly stagnant conditions caused by the presumed equilibrium between the Saronikos Gulf
sea breeze and an opposing synoptic flow is identified as the principal mechanism leading to high pollution episodes in Athens
during the summer. However, previous experimental work has not examined in detail the interaction of the sea breeze flow with
the opposing background flow. In this context, recent experimental work covering the basic key-locations of the Athens Basin
focused on the inland propagation of the southerly sea breeze from the coast to the northern part of the basin mainly under
moderate northerly background wind. During this campaign, a network of four meteorological stations established along the
Athens Basin and a high range acoustic sounder at the centre of Athens operated over a two months time period in the summer
of 1993. In addition, tethered balloon flights in the centre of Athens and on a sea vessel about 15 km offshore were employed
during an experimental day with moderate opposing background wind. The results from this experimental campaign include the
documentation of the sea breeze delay and its intensity as a function of a sea breeze index and features of the vertical structure
of the sea breeze over land as well as over sea.
Received March 20, 1998 Revised October 12, 1998 相似文献
64.
A. F. Velegrakis E. Oikonomou A. Theocharis M. B. Collins H. Kontoyiannis V. Papadopoulos G. Voulgaris T. Wells E. Balopoulos 《Progress in Oceanography》1999,44(4):1131
Internal waves have been detected on ERS-1 SAR images obtained during late summer over the eastern Cretan Straits, an area characterised by complex regional physiography, bottom topography, flow regime and stratification patterns of the upper part of the water column. Analysis of the imaged characteristics of the internal waves has revealed a strong diversity in form, propagation direction and type of sea surface modulation, which indicates various mechanisms of generation. Analysis of the currents recorded over the area shows that, although semi-diurnal tidal currents are present, these are of low magnitude in comparison with the overall flow and, therefore, tidal forcing is unlikely to be a major process in the generation of the imaged internal waves. In addition, a well-defined front has been identified within the Rhodes Strait. This front is considered to be the surficial manifestation of the Asia Minor Current, which is a strong and persistent large-scale circulation feature of the Eastern Mediterranean. 相似文献
65.
Dimitris Papadopoulos Michael Herty Volker Rath Marek Behr 《Computational Geosciences》2011,15(4):737-753
A shape reconstruction method for geophysical objects by temperature measurements is presented which uses adjoint equations
and a level set function approach. Temperature is measured on subdomains, e.g., representing boreholes. This information is
used to reconstruct the shape of the geophysical layers. For this purpose, shape optimization techniques are applied. The
method uses a representation of the layers by a so-called level set function. The evolution of this level set function is
then used to determine the optimal shape. The “speed” of the evolution is computed using adjoint equations. Synthetic examples
demonstrate the use of the inverse method and its behavior in different configurations. 相似文献
66.
We obtain thex - p
xPoincare phase plane for a two dimensional, resonant, galactic type Hamiltonian using conventional numerical integration,
a second order symplectic integrator and a map based on the averaged Hamiltonian. It is found that all three methods give
good results, for small values of the perturbation parameter, while the symplectic integrator does a better job than the mapping,
for large perturbations. The dynamical spectra are used to distinguish between regular and chaotic motion. 相似文献
67.
We construct a 2D-dynamical model in order to study the motion in a galaxy with a double nucleus. Numerical calculations show that the majority of high energy stars, near the double nuclear region, are on chaotic orbits. On the contrary, low energy stars are on chaotic orbits only near massive nuclei while, for less massive nuclei, the motion is regular. Using a semi-numerical approach we explain the chaotic scattering of orbits near each nucleus. The high values of the velocities near the dense nuclei are also explained. Computation of the LCEs indicates a very high degree of chaos. The results derived from our double nucleus dynamical model are compared with models with single ones. Our outcomes are in satisfactory agreement with observational data for the double nucleus system . 相似文献
68.
C. Emdad Haque Dale Dominey-Howes Nuray Karanci Gerassimos Papadopoulos Ahmet Yalciner 《Natural Hazards》2003,29(3):307-308
Editorial Introduction
Editorial 相似文献69.
C. Estournel V. Zervakis P. Marsaleix A. Papadopoulos F. Auclair L. Perivoliotis E. Tragou 《Continental Shelf Research》2005,25(19-20):2366
Observations of dense water formation on the shelf of the Gulf of Thermaikos (North Aegean) are presented, based mainly on continuous monitoring of temperature and currents, during the winter of 2001–2002, at an instrumented mooring and a CTD survey carried out in early February 2002. A 2.5-month realistic simulation, corresponding to the period of observation, was performed to investigate the processes of dense water formation and cascading. The simulation is first compared to the main characteristics of the dense water, time variation of bottom temperature and spatial distribution of the dense water on the shelf. Subsequently, the simulation is used (a) to show that the formation of dense water takes place within the semi-enclosed Thessaloniki Bay and (b) to explain the intermittence of cascading out of the bay in relation to wind variations. The pathways of the dense water through the shelf are investigated with an emphasis on the role of the bottom slope and friction in the Ekman layer. The export of dense water towards the open sea occurs primarily along the slope bounding the western coast. 相似文献
70.
Tatyana Novikova Gerassimos A. Papadopoulos Vassilios Karastathis 《Natural Hazards》2007,40(3):537-552
In the present paper we analyze the effect of local geology on ground motion by means of numerical calculations (numerical
models) using total (TS) and effective stress (ES) methods. These numerical calculations have been applied to the site of
Itea, Corinth Gulf, which was chosen based on liquefaction susceptibility criteria and field inspection. Data from seismic
refraction experiments and cone penetration test N-values as well as selected records of ground motion in nearby areas were
used to construct the input file for the numerical model. By means of␣dynamic analysis such characteristics of ground motion
as acceleration time histories, response spectra, and amplification function were evaluated. A one-dimensional soil amplification
effect was clearly shown. Liquefaction probability at the Itea site was predicted based on the safety factor and the calculation
of the induced settlement at the test site. Results of the TS and ES modeling lead us to conclude: (1) the presence of soft
soil at Itea caused significant amplification (almost 2.5-fold higher magnitude) of the underlying bedrock motion and, therefore,
can contribute to damage; (2) the area of Itea is highly susceptible to liquefaction due to presence of silty sand deposits
at depths between 2.48 m (the position of the water table) and 12 m that demonstrate the rapid growth of the excess pore water
pressure (EPWP) ratio with an increase in peak ground acceleration values. 相似文献