Age and growth rate determinations for the atlantic ribbed mussel,Geukensia demissa Dillwyn (Bivalvia: Mytilidae)

Field studies were conducted in Westport, Connecticut, to determine linear shell growth rates forGeukensia demissa. These rates were then compared with those reported for the same species from other locations. Most shell deposition occurred from March through November of each year. Winter interruptions in growth were clearly recognized in all size mussels and the rings were a reliable method for determining age in mussels from Westport. No significant sexual dimorphism in mean annual growth rates was detected. Age-size relationships based on internal shell lines appear to be less reliable, probably because of the interference by shell erosion at the umbo in this species. No well-defined latitudinal patterns in growth could be established forGeukensia demissa.     

Effect of the solids retention time on the rate of biodegradation of organic compounds

The paper studies the effect of the solids retention time (SRT) on the rate of biodegradation of morpholine (M), sulfanilic acid (SA), nitrilotriacetic acid (NTA), and ethylenediaminetetraacetic acid (EDTA) in laboratory mixed culture systems, fed semicontinuously on a once-a-day feeding schedule. It has been found that the minimum values of SRT at which microorganisms degrading the above compounds were washed out from the cultivation systems were 3, 1, 1, and 20 days for M, SA, NTA, and EDTA systems, respectively. A critical value of SRT was defined as that below which the rate of substrate removal is lower than the rate of substrate application into the system. The critical values of SRT were found to be 8, 3, 2.5, and above 20 days for M, SA, NTA, and EDTA systems, respectively. In a range between the minimum and critical values of SRT the mixed culture system cannot give stable efficiency of a given compound removal and the effluent concentration can be expected to vary considerably. Above the critical value of SRT, every cultivation system has a potential capability of shock loading treatment.     

Asthenospheric parameters of dipping plate regions by magnetotelluric investigations

The multifrequency resolving capability of the electromagnetic surface impedance parameter, employed in magnetotelluric investigations, has been examined for an upper mantle model incorporating (1) a deep-seated lithosphere-asthenosphere boundary and (2) preferred orientations of olivine crystals in the lithosphere, usually associated with the subducting plate boundary zones. Numerical results display the quantitative errors in the resolution of various anisotropic and dipping plate conditions. It is found that (1) conductivity anisotropy, particularly with higher dips, causes a significant dispersion in the impedance values and higher resolving power, and (2) variations in the geometrical/physical parameters are reflected predominantly in the phase component of the surface impedance. The study has relevance to the understanding of the electrical nature of materials, its relationship with physical properties and associated geothermal and seismic activities in the dipping plate regions.     

Are Taxonomic Distinctness measures compliant to other ecological indicators in assessing ecological status?

Assessing the ecological status, a concept implemented in the European Water Framework Directive [EC, 2000. Directive of the European Parliament and of the Council 2000/60/EC establishing a framework for community action in the field of water policy PE-CONS 3639/1/00, p. 72], requires the application of methods capable of distinguishing different levels of ecological quality. The Average Taxonomic Distinctness has been used as tool in this context, and we tested the robustness of Taxonomic Distinctness measures applying it in different scenarios (estuarine eutrophication, organic pollution, and re-colonisation after physical disturbance), analysing simultaneously its compliance to other types of ecological indicators. Results show that, in most of the case studies, only Total Taxonomic Distinctness was relatively satisfactory in discriminating between disturbed situations. Other Taxonomic Distinctness measures have not proved to be more sensitive than other ecological indicators (Shannon-Wiener, Margalef, and Eco-Exergy indices). Therefore, this approach does not seem to be particularly helpful in assessing systems' ecological status with regard to the WFD implementation.     

Characterization of potential zones of dust generation at eleven stations in the southern Sahara

Summary Synoptic wind data for multi-decadal periods at eleven stations located in the southern Sahara region (Agadez, Atar, Bilma, Dori, Gao, Kayes, Nema, Niamey, Nouadhibou, Ouagadougou and Tessalit) are used to study the monthly dust deflation power over the region. We found that, regardless of the conditions of the soil, the deflation power (or wind efficiency) is not sufficient to generate significant amounts of aerosols south of 15°N. North of this latitude, the deflation power is much larger, with potential zones of either very strong deflation (Nouadhibou and Bilma) or severe deflation (Gao, Tessalit, Nema, Atar, Agadez). Stations in the Sahel region such as Gao, Agadez and Tessalit are characterized by a gradual reinforcement of the deflation power between 1970 and 1984 in correspondence of increasing desertification over the region. During this same period, Bilma, a well know region of dust source, experienced a major reduction in deflation power due to shifts in large scale wind patterns.     

New Calculation of the Electrical Microfield Distribution in Plasma

Recently new calculations for the probability field distribution in plasma generating a new expression for the Debye screening fields was carried out by Martin and Perez (1996). This field is a very accurate solution of the Poisson equation for a point test charge in a plasma described by a uniform charge density at Boltzmann thermal equilibrium. The method that we here present is based mainly on the introduction of this adequate field considering the dependence of the potential with the magnitude of the test charge in the calculus of the distribution. First we find the spectral function F(k) carrying out the Fourier transform of the field which is numerically calculated for each representative value of the variable in k space and then fitting these data in order to get F(k). Thus, after the usual numerical integration on the wave number space d³k, the field strength distribution is achieved. This approximation recovers the Holtsmark distribution in the limit of high temperature, and/or, small densities as also these where 0. As in previous works (Ecker, 1972; Spatschek, 1990) the most probable value of the field decreases as the temperature is reduced, and/or, the density increased.