Exhaustive test sets for algebraic specifications

In the context of testing from algebraic specifications, test cases are ground formulas chosen amongst the ground semantic consequences of the specification, according to some possible additional observability conditions. A test set is said to be exhaustive if every programme P passing all the tests is correct and if for every incorrect programme P, there exists a test case on which P fails. Because correctness can be proved by testing on such a test set, it is an appropriate basis for the selection of a test set of practical size. The largest candidate test set is the set of observable consequences of the specification. However, depending on the nature of specifications and programmes, this set is not necessarily exhaustive. In this paper, we study conditions to ensure the exhaustiveness property of this set for several algebraic formalisms (equational, conditional positive, quantifier free and with quantifiers) and several test hypotheses. Copyright © 2016 John Wiley & Sons, Ltd.     

Radon hazard in shallow groundwaters II: dry season fracture drainage and alluvial fan upwelling

²²²Rn concentrations have been measured in a well located on the edge of a large Pleistocene-Holocene fan and belonging to the shallow pyroclastic aquifer of the Pietramelara Plain, southern Italy. The aim of this study has been both to characterise the hydrological inputs that determine the influx of ²²²Rn to the shallow aquifer and to understand the correlations between ²²²Rn, major ions, physical-chemical parameters and rainfall. Results obtained from the time series indicate that the studied well shows a ²²²Rn variability that is inconsistent with a mechanism of pure hydrological amplification, such as described in Radon hazard in shallow groundwaters: Amplification and long term variability induced by rainfall (De Francesco et al., 2010a). On the contrary, in this well hydrological amplification appears to be mainly tied to the upwelling of alluvial fan waters, rich in radon, in response to pistoning from recharge in the carbonate substrate. This upwelling of alluvial fan waters occurs during almost the whole period of the annual recharge and is also responsible of the constant increase in ²²²Rn levels during the autumn-spring period, when both the water table level and weekly rainfall totals drop. Furthermore, a rapid delivery mechanism for ²²²Rn likely operates through fracture drainage in concomitance with the very first late summer-early autumn rains, when rainfall totals appear largely insufficient to saturate the soil storage capacity. Results obtained from this study appear to be particularly significant in both radon hazard zoning in relation to the shallow aquifer and possibly also for indoor radon, owing to possible shallow aquifer-soil-building exchanges. Moreover, both the spike-like events and the long wave monthly scale background fluctuations detected can also have potential significance in interpreting ²²²Rn time series data as seismic and/or volcanic precursors. Finally, ²²²Rn has proved to be an excellent tracer for hydrological inputs to the shallow aquifer when combined with major ions, physical-chemical data and geological and geomorphological controls.     

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Organisational motives and spatial effects in Internet adoption and intensity of use: evidence from French industrial firms

The aim of this study is to examine the reasons why firms use ICTs at varying rates, by making a distinction between the two stages of their diffusion: their adoption and the intensity of their use. What are the differences between Internet adopters (in terms of their internal organization and external environment) that explain the intensity with which they use this technology? Furthermore, do these processes vary according to the type of area in which firms are located (urban vs. rural)? A model of technological diffusion is constructed that merges two types of models: those that concentrate on epidemic effects and the so-called equilibrium models that consider the decision to adopt new technologies as a result of an economic calculation by firms. To test this model, we use data drawn from a recent French national survey of 5,200 industrial firms (“ICT and E-commerce”, 2002). One striking result of this study is that we do not obtain a significant positive correlation between firm’s size and Internet intensity of use. Moreover, though spatial disparities related to ICT adoption are no longer significant in France, they remain very important in the processes of ICT appropriation and use by firms. The results also indicate that the determinants of the intensity of Internet use vary significantly according to the firms’ location: epidemics effects play an essential role in the case of urban the firms, while rank effects are essential in low density areas.     

Scalar energy fluctuations in Large-Eddy Simulation of turbulent flames: Statistical budgets and mesh quality criterion

Large-Eddy Simulation (LES) provides space-filtered quantities to compare with measurements, which usually have been obtained using a different filtering operation; hence, numerical and experimental results can be examined side-by-side in a statistical sense only. Instantaneous, space-filtered and statistically time-averaged signals feature different characteristic length-scales, which can be combined in dimensionless ratios. From two canonical manufactured turbulent solutions, a turbulent flame and a passive scalar turbulent mixing layer, the critical values of these ratios under which measured and computed variances (resolved plus sub-grid scale) can be compared without resorting to additional residual terms are first determined. It is shown that actual Direct Numerical Simulation can hardly accommodate a sufficiently large range of length-scales to perform statistical studies of LES filtered reactive scalar-fields energy budget based on sub-grid scale variances; an estimation of the minimum Reynolds number allowing for such DNS studies is given. From these developments, a reliability mesh criterion emerges for scalar LES and scaling for scalar sub-grid scale energy is discussed.     

Multidimensional flamelet-generated manifolds for partially premixed combustion

Flamelet-generated manifolds have been restricted so far to premixed or diffusion flame archetypes, even though the resulting tables have been applied to nonpremixed and partially premixed flame simulations. By using a projection of the full set of mass conservation species balance equations into a restricted subset of the composition space, unsteady multidimensional flamelet governing equations are derived from first principles, under given hypotheses. During the projection, as in usual one-dimensional flamelets, the tangential strain rate of scalar isosurfaces is expressed in the form of the scalar dissipation rates of the control parameters of the multidimensional flamelet-generated manifold (MFM), which is tested in its five-dimensional form for partially premixed combustion, with two composition space directions and three scalar dissipation rates. It is shown that strain-rate-induced effects can hardly be fully neglected in chemistry tabulation of partially premixed combustion, because of fluxes across iso-equivalence-ratio and iso-progress-of-reaction surfaces. This is illustrated by comparing the 5D flamelet-generated manifold with one-dimensional premixed flame and unsteady strained diffusion flame composition space trajectories. The formal links between the asymptotic behavior of MFM and stratified flame, weakly varying partially premixed front, triple-flame, premixed and nonpremixed edge flames are also evidenced.