Genetic structure in the Mediterranean seagrass Posidonia oceanica: disentangling past vicariance events from contemporary patterns of gene flow.

The Mediterranean Sea is a two-basin system, with the boundary zone restricted to the Strait of Sicily and the narrow Strait of Messina. Two main population groups are recognized in the Mediterranean endemic seagrass Posidonia oceanica, corresponding to the Western and the Eastern basins. To address the nature of the East-West cleavage in P. oceanica, the main aims of this study were: (i) to define the genetic structure within the potential contact zone (i.e. the Strait of Sicily) and clarify the extent of gene flow between the two population groups, and (ii) to investigate the role of present water circulation patterns vs. past evolutionary events on the observed genetic pattern. To achieve these goals, we utilized SSR markers and we simulated, with respect to current regime, the possible present-day dispersal pattern of Posidonia floating fruits using 28-day numerical Lagrangian trajectories. The results obtained confirm the presence of the two main population groups, without any indices of reproductive isolation, with the break zone located at the level of the Southern tip of Calabria. The populations in the Strait of Sicily showed higher affinity with Western than with Eastern populations. This pattern of genetic structure probably reflects historical avenues of recolonization from relict glacial areas and past vicariance events, but seems to persist as a result of the low connectivity among populations via marine currents, as suggested by our dispersal simulation analysis.

Near-field dispersion of produced formation water (PFW) in the Adriatic Sea: an integrated numerical-chemical approach.

Produced formation waters (PFWs), a by-product of both oil and gas extraction, are separated from hydrocarbons onboard oil platforms and then discharged into the sea through submarine outfalls. The dispersion of PFWs into the environment may have a potential impact on marine ecosystems. We reproduce the initial PFW-seawater mixing process by means of the UM3 model applied to offshore natural gas platforms currently active in the Northern Adriatic Sea (Mediterranean Sea). Chemical analyses lead to the identification of a chemical tracer (diethylene glycol) which enables us to follow the fate of PFWs into receiving waters. The numerical simulations are realized in different seasonal conditions using both measured oceanographic data and tracer concentrations. The numerical results show the spatial and temporal plume development in different stratification and ambient current conditions. The analytical approach measures concentrations of the diethylene glycol at a maximum sampling distance of 25 m. The results show a good agreement between field observations and model predictions in the near-field area. The integration of numerical results with chemical analyses also provides new insight to plan and optimize PFW monitoring and discharge.

Transport in finite size systems: An exit time approach.

In the framework of chaotic scattering we analyze passive tracer transport in finite systems. In particular, we study models with open streamlines and a finite number of recirculation zones. In the nontrivial case with a small number of recirculation zones a description by means of asymptotic quantities (such as the eddy diffusivity) is not appropriate. The nonasymptotic properties of dispersion are characterized by means of the exit time statistics, which shows strong sensitivity on initial conditions. This yields a probability distribution function with long tails, making impossible a characterization in terms of a unique typical exit time. (c) 1999 American Institute of Physics.

The optical-geometrical illusion "corner Poggendorff" re-examined.

In 1988 Greene noted, if a straight pair of obliques are drawn outside of two orthogonal lines, the segments appears to be angled slightly one relative to the other. This illusion, designated as "corner Poggendorff" is different from the Poggendorff effect (the two obliques seem to lie on a parallel path). The results of the present experiments (N = 76 students) suggest that the general conditions for the corner Poggendorff are similar to those for the Judd illusion.

Obliquity integration: variations on a theme of Delboeuf.

An optical-geometrical illusion, described by Delboeuf and not familiar to specialists, is investigated. The results of two experiments show that the divergence between a bar filled with parallel slanting lines and a line drawn above it is clearly related to this angle of the lines which fill the bar. The illusion is already present when this angle is 10 degrees, reaches its maximum at 20 degrees, decreases at 30 degrees, and almost disappears at 40 degrees. These results are similar to those found for the tilt illusion, are slightly different from those found for the rod-and-frame illusion, and differ greatly from those found for the Zöllner illusion. The other variables considered-the distance between the slanting lines filling up the bar, the distance between the upper line and the bar, and the width of the bar--do not influence the illusion as much. Since either the line appears as diverging from the bar, or the bar seems inclined in relation to the line, the illusion should be considered a complex one. The small oblique lines inside the bar induce obliquity in the opposite sense in the display, but which of the elements is seen as diverging from the other depends on which of the two is established as the frame of reference.

[Pentoxifylline and arterial hypertension in diabetes mellitus: long-term results in randomized groups]. / Pentossifillina ed ipertensione arteriosa nel diabete mellito: risultati a lungo termine in gruppi randomizzati.

This follow-up study concerns the use of pentoxifylline (PTX) as antihypertensive drug in randomized diabetic groups. A significant reduction of systolic and diastolic arterial blood pressure has been obtained in diabetic patients treated with PTX alone or with PTX associated to conventional antihypertensive therapy. The normalization of arterial blood pressure was associated to an improvement of erythrocyte filterability and to a reduction of proteinuria. Therefore, pentoxifylline can be considered a good pharmacological approach in the treatment of diabetic hypertension and in the prevention of diabetic renal disease.