Elastic properties and stability of coexisting 3T and 2M 1 phengite polytypes

The elastic properties of coexisting natural 3T and 2M ₁ phengite samples (Cima Pal, Sesia Zone; Val Savenca; Western Alps, Italy) with similar chemical compositions have been studied by room temperature–high pressure powder diffraction, using synchrotron radiation on the ID9A beam-line at ESRF (Grenoble, France). The P–V curves have been modelled by the Birch–Murnaghan model; a third-order expansion fitted to the experimental data yields for 3T and 2M ₁ K ₀=60.4(±0.7) GPa, K′=5.79(±0.11) at V ₀=703.8851 ų, and K ₀=57.3(±1.0) GPa, K′=6.97(±0.24) at V ₀=938.8815 ų, respectively. The relative stability of 3T vs. 2M ₁ has been explored as a function of pressure and temperature in terms of configuration and deformation contributions to the Gibbs energy, using the elastic properties determined here and other thermodynamic parameters from earlier investigations. The results presented agree with the hypothesis of stability of the 3T polytype in the high pressure regime.     

Modeling water resources of a highly irrigated alluvial plain (Italy): calibrating soil and groundwater models

Modern and effective water management in large alluvial plains that have intensive agricultural activity requires the integrated modeling of soil and groundwater. The models should be complex enough to properly simulate several, often non-linear, processes, but simple enough to be effectively calibrated with the available data. An operative, practical approach to calibration is proposed, based on three main aspects. First, the coupling of two models built on well-validated algorithms, to simulate (1) the irrigation system and the soil water balance in the unsaturated zone and (2) the groundwater flow. Second, the solution of the inverse problem of groundwater hydrology with the comparison model method to calibrate the model. Third, the use of appropriate criteria and cross-checks (comparison of the calibration results and of the model outputs with hydraulic and hydrogeological data) to choose the final parameter sets that warrant the physical coherence of the model. The approach has been tested by application to a large and intensively irrigated alluvial basin in northern Italy.     

OH incorporation in nearly pure MgAl2O4 natural and synthetic spinels

Four nearly pure MgAl₂O₄ spinels, of both natural and synthetic occurrence, have been studied by means of X-ray single crystal diffraction and FTIR spectroscopy in order to detect their potential OH content. Absorption bands that can be assigned to OH incorporated in the spinel structure were only observed in spectra of a non-stoichiometric synthetic sample. The absorption intensity of two bands occurring at 3350 and 3548 cm⁻¹ indicate an OH content of 90 ppm H₂O. Based on correlations of OH vibrational frequencies and O-H?O distances, the observed absorption bands correspond to O-H?O distances of 2.77 and 2.99 Å, respectively, which is close to the values obtained by the structure refinements for ^VIO-O_unsh (2.825 Å) and ^IVO-O (3.001 Å). This indicates that one probable local position for hydrogen incorporation is the oxygens coordinating a vacant tetrahedral site. The present spectra demonstrate that the detection limit for OH in Fe-free spinels is in the range 10-20 ppm H₂O. However, at appreciable Fe²⁺ levels, the detection of OH bands becomes hampered due to overlap with strong absorption bands caused by electronic d-d transitions in Fe²⁺ in the tetrahedral position.     

A micro-Mössbauer study of chromites included in diamond and other mantle-related rocks

Oxygen fugacity ( $ f_{{{\text{O}}_{ 2} }} $ f O 2 ) is a fundamental but little known intensive variable in mantle processes. It influences the P/T position of a mantle solidus and the composition of mantle-derived melts and fluids and constrains mantle-core equilibria and a number of geophysical properties of the mantle. An important source of information on oxidation states is the ferric–ferrous iron ratio in mantle spinels. Since the magnetite component is low in mantle spinels, normal analytical errors translate into considerable $ f_{{{\text{O}}_{ 2} }} $ f O 2 uncertainties. In this study, we analyzed the Fe³⁺–Fe_tot ratio of chromites present as inclusions in diamond and other mantle-related occurrences by point-source Mössbauer spectroscopy using single-crystal absorbers as well as conventional Mössbauer spectroscopy using powder absorbers. The studied spinels have been previously analyzed by single-crystal X-ray diffraction and electron microprobe. The ferric–ferrous ratios found are normally similar to the different techniques apart from some samples where a large number of grains have been used for the analyses (powder absorbers). The general agreement between the different techniques allows us to conclude that the studied chromites are stoichiometric. However, conventional Mössbauer spectroscopy on powder absorbers should be conducted with great care, since the method requires a relatively large amount of sample material. Spinel frequently occurs as small grains, and the large number of crystals required may possess different degrees of oxidation/alteration and, consequently, different ferric–ferrous ratio leading to possible errors in the interpretation of the results.     

Turbulent Intensities and Velocity Spectra for Bare and Forested Gentle Hills: Flume Experiments

To investigate how velocity variances and spectra are modified by the simultaneous action of topography and canopy, two flume experiments were carried out on a train of gentle cosine hills differing in surface cover. The first experiment was conducted above a bare surface while the second experiment was conducted within and above a densely arrayed rod canopy. The velocity variances and spectra from these two experiments were compared in the middle, inner, and near-surface layers. In the middle layer, and for the canopy surface, longitudinal and vertical velocity variances () were in phase with the hill-induced spatial mean velocity perturbation (Δu) around the so-called background state (taken here as the longitudinal mean at a given height) as predicted by rapid distortion theory (RDT). However, for the bare surface case, and remained out of phase with Δu by about L/2, where L is the hill half-length. In the canopy layer, wake production was a significant source of turbulent energy for , and its action was to re-align velocity variances with Δu in those layers, a mechanism completely absent for the bare surface case. Such a lower ‘boundary condition’ resulted in longitudinal variations of to be nearly in phase with Δu above the canopy surface. In the inner and middle layers, the spectral distortions by the hill remained significant for the background state of the bare surface case but not for the canopy surface case. In particular, in the inner and middle layers of the bare surface case, the effective exponents derived from the locally measured power spectra diverged from their expected  − 5/3 value for inertial subrange scales. These departures spatially correlated with the hill surface. However, for the canopy surface case, the spectral exponents were near  − 5/3 above the canopy though the minor differences from  − 5/3 were also correlated with the hill surface. Inside the canopy, wake production and energy short-circuiting resulted in significant departures from  − 5/3. These departures from  − 5/3 also appeared correlated with the hill surface through the wake production contribution and its alignment with Δu. Moreover, scales commensurate with Von Karman street vorticies well described wake production scales inside the canopy, confirming the important role of the mean flow in producing wakes. The spectra inside the canopy on the lee side of the hill, where a negative mean flow delineated a recirculation zone, suggested that the wake production scales there were ‘broader’ when compared to their counterpart outside the recirculation zone. Inside the recirculation zone, there was significantly more energy at higher frequencies when compared to regions outside the recirculation zone.     

Long-term model of planimetric and bathymetric evolution of a tidal lagoon

This model is based on the concept of transport concentration, defined as the time-averaged concentration in a given location of a lagoon, which determines the long-term net transport of sediments as the sum of a dispersive and an advective flux. Dispersive net flux of sediments is due to the alternate components of the tidal flow, while the advective net flux of sediments is due to the residual (Eulerian) component of the tidal, fluvial and littoral flow and possibly to the asymmetry between flow and ebb tide.     

A semi-empirical approach to model pressure dependence of elastic moduli in granular media accounting for variations of coordination-number and Poisson-ratio

The effective medium theory based on the Hertz–Mindlin contact law is the most popular theory to relate dynamic elastic moduli (or elastic velocities) and confining pressure in dry granular media. However, many experimental results proved that the effective medium theory predicts pressure trends lower than experimental ones and over-predicts the shear modulus. To mitigate these mispredictions, several evolutions of the effective medium theory have been presented in the literature. Among these, the model named modified grain contact theory is an empirical approach in which three parametric curves are included in the effective medium theory model. Fitting the parameters of these curves permits to adjust the pressure trends of the Poisson ratio and the bulk modulus. In this paper, we present two variations of the modified grain contact theory model. First, we propose a minor modification in the fitting function for the porosity dependence of the calibration parameters that accounts for non-linearity in the vicinity of the critical porosity. Second, we propose a major modification that reduces the three-step modified grain contact theory model to a two-step model, by skipping the calibration parameter–porosity fit in the model and directly modelling the calibration parameter–pressure relation. In addition to an increased simplicity (the fitting parameters are reduced from 10 to 6), avoiding the porosity fit permits us to apply the model to laboratory data that are not provided with accurate porosity measurements. For this second model, we also estimate the uncertainty of the fitting parameters and the elastic velocities. We tested this model on dry core measurements from literature and we verified that it returns elastic velocity trends as good as the original modified grain contact theory model with a reduced number of fitting parameters. Possible developments of the new model to add predictive power are also discussed.     

Outlier detection with partial information: application to emergency mapping

This paper, addresses the problem of novelty detection in the case that the observed data is a mixture of a known ‘background’ process contaminated with an unknown other process, which generates the outliers, or novel observations. The framework we describe here is quite general, employing univariate classification with incomplete information, based on knowledge of the distribution (the probability density function, pdf) of the data generated by the ‘background’ process. The relative proportion of this ‘background’ component (the prior ‘background’ probability), the pdf and the prior probabilities of all other components are all assumed unknown. The main contribution is a new classification scheme that identifies the maximum proportion of observed data following the known ‘background’ distribution. The method exploits the Kolmogorov–Smirnov test to estimate the proportions, and afterwards data are Bayes optimally separated. Results, demonstrated with synthetic data, show that this approach can produce more reliable results than a standard novelty detection scheme. The classification algorithm is then applied to the problem of identifying outliers in the SIC2004 data set, in order to detect the radioactive release simulated in the ‘joker’ data set. We propose this method as a reliable means of novelty detection in the emergency situation which can also be used to identify outliers prior to the application of a more general automatic mapping algorithm.

---