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The paper theoretically investigates the stability properties of the dam-break wave of a fluid with power-law rheology. Assuming the long-wave approximation, a depth-averaged flow model is considered. The linear stability analysis of the wave is carried out to individuate the marginal stability conditions. To this aim, the multiple-scale technique is applied with reference to the kinematic wave solution, which formally limits the validity of the theoretical achievements to relatively long time scales. Both shear-thinning and shear-thickening fluids are considered. Similarly to the case with uniform conditions, the analysis indicates that stable conditions can be associated with a marginal value of the Froude number. However, differently from the uniform conditions, the marginal Froude number is shown to be a function not only of the power-law index but also of the streamwise gradient of the base flow velocity and of the disturbance wavelength. The critical Froude number is found to be larger than the corresponding one in uniform conditions. Numerical solutions of the full model confirmed the outcomes of the linear stability analysis for both shear-thinning and shear-thickening fluids. [ABSTRACT FROM AUTHOR]

A comparative study of topoisomerase activity in two European crayfish species Astacus astacus and Austropotamobius pallipes was carried out to determine the physiological basis of the difference in ecological fitness of these systematically related crayfish species. Topoisomerase activity was present in both species. Adult males were kept for a week at the temperatures of 4, 15 and 25°C. Topoisomerase activity was measured in the hepatopancreas, the muscle tissue and the spermiducts. It was present in the hepatopancreas of Atacus astacus at the three tested temperatures and in Austropotamobius pallipes only at the temperatures of 4 and 15°C. No topoisomerase activity was registered in the muscle tissue and in the spermiducts. Taken together these data indicate that topoisomerase activity can be a useful marker for crayfish viability.

Oxidative damage reflects an imbalance between the production of oxidants and removal or scavenging of those oxidants. The antioxidants neutralize via enzymatic and non-enzymatic mechanisms the toxic effects of the free radicals, acting at different levels both within the cell and in the extra cellular fluids. A study on the oxidative defenses under conditions of stress temperature was carried out in the freshwater crayfish Austropotamobius pallipes italicus, an endangered species now distributed in scattered areas in Italy and a few Europeans countries. Glutatione peroxidase (GPX) and Glutatione reductase (GR) activity have been measured in the hemolymph, hepatopancreas and muscle tissue by an enzymatic assay in male individuals exposed, for seven days, to three different temperature: 4 °C, 15 °C and 25 °C. Antioxidative enzyme activity was found in the hemolymph, but not in the hepatopancreas and in the muscle tissue. The enzyme activity varied in the hemolymph according to the temperature the animals were exposed to. As far as the GPX is concerned we found the activity only in the hemolymph of animals exposed to the temperature of 15 °C. On the contrary, GR activity was detected in the hemolymph at the three considered temperatures. Although the highest level of GR activity was found at 25 °C, followed by 4 °C and 15 °C, it was nonetheless very low and much lower than the level of GPX activity. Very little is known on oxidative stress in crustaceans and virtually nothing in the freshwater crayfish A. pallipes italicus. Our data, although preliminary, indicate that the antioxidant defenses provide a useful criterion for the thermal tolerance in studies on natural distribution and suitability of aquacultural environments.

Urban drainage networks (UDNs) represent important infrastructures to protect and maintain community health and safety. For these reasons, technicians and researcher are focusing more and more on topics related to vulnerability, resilience and monitoring for controlling illicit intrusions, contaminant and pathogenic spread. In the last years the complex network theory (CNT) is attracting attention as a new, useful and structured approach to analyze urban systems. The aim of this work is to evaluate potentialities of CNT approaches for UDNs vulnerability assessment and monitoring system planning. Limits and potentialities of applicability of CNT tools to UDNs are first provided evaluating the performances of standard centrality metrics. Then, it is proposed the use of tailored metrics embedding prior information, as intrinsic relevance of each node and pipe flow direction, which derive from the Horton's hierarchy and geometric data (pipe slope), respectively, without performing hydraulic simulations. The analysis is applied on two schematic literature networks of different complexity and to a real case‐study. The results suggest that vulnerability/resilience, monitoring design, contaminant and pathogenic spreads can be effectively analyzed using tailored metrics. Therefore, the proposed approach represents a complementary tool respect the more complex and computationally expensive methodologies and it is particular useful for large complex networks. Plain Language Summary: Urban drainage systems are networked infrastructure strongly conditioned by their topology. Tailored complex network theory approach represents a complementary tool to characterize the urban drainage network (UDN) behavior with respect to vulnerability, monitoring design, contaminant and pathogenic spreads. Key Points: Potentialities of complex network theory (CNT) for urban drainage network analysisTailored CNT tools embedding prior information for urban drainage network analysisVulnerability, monitoring design, contaminant and pathogenic spreads analysis of urban drainage networks [ABSTRACT FROM AUTHOR]

We have developed a technique and a prototype for [Beta]-ray quantitative imaging of biological samples which have been radioactively labeled. The prototype is based on a solid state pixel detector, bump-bonded to a low threshold, single particle counting chip: the detector we used is 200-[micro]m thick GaAs, with pixel size 170 [micro]m. In this paper we describe an experiment that shows the capability of monitoring a dynamic process. Specifically, [[sup.14]C]L-Leucine uptake by eggs of mollusk cephalopod Octopus vulgaris and the consequent migration of marker into the ooplasm was followed.

The paper investigates the influence of the inlet boundary condition on the spatial evolution of natural roll-waves in a power-law fluid flowing in steep slope channels. The analysis is carried out numerically, by solving the von Kármán depth-integrated mass and momentum conservation equations, in the long-wave approximation. A second-order accurate scheme is adopted and a small random white-noise is superposed to the discharge at the channel inlet to generate the natural roll-waves train. Both shear-thinning and shearthickening power-law fluids are investigated, considering uniform, accelerated and decelerated hypercritical profiles as the unperturbed condition. Independently of the unperturbed profile and of the fluid rheology, numerical simulations clearly enlighten the presence of coalescence, coarsening and overtaking processes, as experimentally observed. All the considered statistical parameters indicate that the natural roll-waves spatial evolution is strongly affected by the unperturbed profile. Compared with the uniform condition, at the beginning of roll-waves development an accelerated profile reduces the growth of the roll-waves with a downstream shift of the non-linear wave interaction. The opposite behavior is observed if the roll wave train develops over a decelerated profile. The comparison with the theoretical outcomes of the linearized near wave-front analysis allows the interpretation of this result in terms of stability of the base flow. It is shown that once the coarsening process starts to take place, the roll-waves spatial growth rate is independent of the unperturbed profile. Present results suggest that an appropriate selection of the flow depth at the channel inlet may contribute to control, either enhancing or inhibiting, the formation of a roll-waves train in power-law fluids. [ABSTRACT FROM AUTHOR]