PROBLEMS IN CONSTRUCTING A BATHYMETRIC BASE MAP FOR THE GULF OF FINLAND

The various steps required for compilation of a bathymetric chart of the Gulf of Finland are outlined, taking into account the specific conditions characteristic of that water body. The use of available initial source materials and special survey work required for supplementing these sources is discussed. Translated by Edward Torrey, Alexandria, VA 22308 from: Geodeziya i kartografiya, 1988, No. 8, pp. 40-42.     

Marine risk assessment: linear alkylbenzenesulponates (LAS) in the North Sea

The fate of linear alkylbenzenesulponates (LAS) in estuaries and coastal areas of the North Sea has been characterized with simple environmental models. The predicted concentration range in the estuaries around the North Sea (0.9-9 microg LAS l(-1)) was validated by monitoring data (1-9 microg LAS l(-1)). In offshore sites of the North Sea, it is estimated--and experimentally verified for a few sites--that the LAS concentration is below analytical detection limit (i.e., 0.5 microg LAS l(-1)). The effects of LAS on marine organisms have been reviewed. For short-term acute tests, there was no significant difference (p = 0.83) between the mean LC50 values of freshwater and marine organisms (mainly pelagic species tested, 4.1 and 4.3 mg LAS l(-1), respectively). For longer-term chronic tests, it appeared that the sensitivity (mean no-observed effect concentration (NOEC) value) of marine and freshwater organisms (0.3 and 2.3 mg LAS l(-1), respectively) was significantly different pt-test = 0.007). The predicted no-effect-concentrations (PNEC) were 360 and 31 microg LAS l(-1), for freshwater and marine pelagic communities, respectively. Given that the maximum expected estuarine and marine concentrations are 3 to > 30 times lower than the PNEC, the risk of LAS to pelagic organisms in these environments is judged to be low.     

Spatio-temporal variability of currents over a mobile dune field in the Dover Strait

A one month field campaign featuring two spring–neap tide cycles and three strong storms has been performed in a mobile dune area located in the central part of the Dover Strait. These dunes are known to move in a complex manner as their migration direction varies in space and time (Le Bot et al., 2000, Le Bot, 2001, Le Bot and Trentesaux, 2004). In order to gain some insights into the dune motion processes we present an analysis of the spatio-temporal variability of currents in the area emphasizing the relative influence of tides and storms. A total of eight different hydro-meteorological regimes have been distinguished during the experiment duration. The analysis of the currents measurements at five locations in the area shows that the eight hydro-meteorological regimes induce very different current responses at the bottom. The residual tidal currents exhibit a significant spatial variability both in direction and in intensity. A numerical model of tidal currents over the Dover Strait confirms the strong spatio-temporal variability of the residual tidal currents featuring three singular points. Amongst them, a saddle point is located just south of the I-dune at the convergence of opposite direction residual tidal currents. The wind-induced currents are almost uniform in space, their intensity and direction however strongly depends on the wind regime and thus on time. The mean total current feature a spatial pattern which can be tidal of wind-induced currents dominated, or either in balance, depending on the regime considered. At the PERMOD campaign time scale, the total current is dominated by the residual tidal current. These results proved to give valuable insights to explain the complex dynamics of dune motion observed in this area by Le Bot et al., 2000, Le Bot, 2001, Le Bot and Trentesaux, 2004 at short and long time scales.     

Expansion of the principal functions of Keplerian motion using complex variables

A special system of canonical variables is considered. An algorithm for expanding the principal functions of Keplerian motion in new elements is presented. The advantage of the proposed system is a relatively small number of terms in the classical expansions of the unperturbed two-body problem. A method for expanding the time derivatives of the rectangular coordinates is proposed. Some estimates of the number of terms in the presented expansions have been obtained through numerical experiments.     

Evolution of disk galaxies regulated by supernova remnants

Assuming that a disk galaxy is composed of an ambient pervasive gas, small clouds, molecular clouds and stars, its evolution is studied through examining the interchange processes among them. Main results obtained are: (1) The star formation rate is directed by the formation process of molecular clouds. (2) Depending upon the parameters there may be three or four types of evolution of disk galaxies: the no star formation case, the active in the past and inactive at present star formation case, the burst-like star formation case and the very active in star formation case.Paper presented at the IAU Third Asian-Pacific Regional Meeting, held in Kyoto, Japan between 30 September–6 October, 1984.     

Existence of transverse waves in anisotropic poroelastic media

Out of the four waves in an anisotropic poroelastic medium, two are termed as quasi-transverse waves. The prefix 'quasi' refers to their polarizations being nearly, but not exactly, perpendicular to direction of propagation. In this composite medium, unlike perfectly elastic medium, the propagation of a longitudinal wave along a phase direction may not be accompanied by transverse waves. The existence of a transverse wave in anisotropic poroelastic media is ensured by the two equations restricting the choice of elastic coefficients of porous aggregate as well as fluid–solid coupling. Necessary and sufficient conditions for the existence of transverse waves along the coordinate axes and in the coordinate planes for general anisotropy are discussed. The discussion is extended to the case of orthotropic materials and existence for few specific phase directions is also explored. The conditions for the transverse waves decided on the basis of their apparent polarizations, that is, particle motion being perpendicular to ray direction, are also discussed. For a particular numerical model, the existence of these apparent transverse waves is solved numerically for phase directions in coordinate planes. For general directions of phase propagation, the existence of these transverse waves is checked graphically for the chosen numerical model.