Testing a new rill flow resistance approach using the Water Erosion Prediction Project experimental database

In this paper, a recently theoretically deduced rill flow resistance equation, based on a power‐velocity profile, was tested using the Water Erosion Prediction Project database. This database includes measurements of flow velocity, water depth, cross section area, wetted perimeter, and bed slope that were made in rills shaped on experimental sites distributed across the continental United States. In particular, three different experimental conditions (only rainfall, only flow, and rain with flow) were examined, and for each condition, the theoretically based relationship for estimating the Γ function of the power velocity profile was calibrated. The results established that (a) the Darcy‐Weisbach friction factor can be accurately estimated using the proposed theoretical approach, and (b) the flow resistance increases with the effect of rainfall impact.     

Estimating flow resistance in steep slope rills

Recent research recognized that the slope of 18% can be used to distinguish between the ‘gentle slope’ case and that of ‘steep slope’ for the detected differences in hydraulic variables (flow depth, velocity, Reynolds number, Froude number) and those representatives of sediment transport (flow transport capacity, actual sediment load). In this paper, using previous measurements carried out in mobile bed rills and flume experiments characterized by steep slopes (i.e., slope greater than or equal to 18%), a theoretical rill flow resistance equation to estimate the Darcy-Weisbach friction factor is tested. The main aim is to deduce a relationship between the velocity profile parameter Γ, the channel slope, the Reynolds number, the Froude number and the textural classes using a data base characterized by a wide range of hydraulic conditions, plot or flume slope (18%–84%) and textural classes (clay ranging from 3% to 71%). The obtained relationship is also tested using 47 experimental runs carried out in the present investigation with mobile bed rills incised in a 18%—sloping plot with a clay loam soil and literature data. The analysis demonstrated that: (1) the soil texture affects the estimate of the Γ parameter and the theoretical flow resistance law (Equation 25), (2) the proposed Equation (25) fits well the independent measurements of the testing data base, (3) the estimate of the Darcy-Weisbach friction factor is affected by the soil particle detachability and transportability and (4) the Darcy-Weisbach friction factor is linearly related to the rill slope.     

Petrogenetic relationships between peralkaline rhyolite dykes and mafic rocks in the post-Variscan gabbroic complex from Bocca di Tenda (northern Corsica, France)

The Lower Permian complex from Bocca di Tenda (Corsica island, France) consists of a gabbroic sequence crosscut by chilled dykes ranging in composition from basalt to trachyandesite and peralkaline rhyolite. The gabbroic sequence is mostly composed of olivine gabbronorites, quartz gabbronorites/diorites locally displaying high ilmenite amounts, and hornblende-rich tonalites. The quartz gabbronorites/diorites and the hornblende-rich tonalites have similar initial ε_Nd values (+0.9 to ?1.1) and record a fractional crystallization process driven by separation of plagioclase, pyroxene, and ilmenite. The olivine gabbronorites have slightly higher initial ε_Nd than the quartz gabbronorites/diorites and the hornblende-rich tonalites, thereby documenting that the early evolution of the melts that gave rise to the gabbroic sequence was controlled by concomitant fractional crystallization and crustal assimilation. The trachyandesite dykes are rare and rich in dark mica. The selected trachyandesite has initial ε_Nd of +0.4, which is slightly lower than the ε_Nd of the basalt dykes. The basalt and the trachyandesite dykes are most likely genetically related through a process of fractional crystallization controlled by segregation of plagioclase, clinopyroxene and minor ilmenite, and assimilation of crustal material. The peralkaline rhyolites have initial ε_Nd values ranging from +0.3 to ?0.3. Whole-rock chemical variations and trace element compositions of Na-amphibole (arfvedsonite) indicate that the peralkaline rhyolite dykes record a process of fractional crystallization mainly controlled by separation of alkali feldspar and minor ilmenite and arfvedsonite. A plausible petrogenetic hypothesis for the genesis of the peralkaline rhyolite melts implies a protracted process of fractional crystallization from the trachyandesitic melts. This fractionation process would be initially ruled by separation of plagioclase, dark mica, and minor ilmenite. An alternative hypothesis for the origin of the peralkaline rhyolite melts implies partial melting of nearly coeval amphibole-rich mafic intrusives, which formed by crustally contaminated mantle-derived melts. The genesis of the peralkaline rhyolites is in any case correlated with mantle-derived melts that experienced extensive crustal contamination.     

Laboratory modeling of topographic Rossby normal modes

The physical modeling of topographic Rossby normal modes carried out at the “Coriolis” Rotating Platform (Grenoble), is presented. The basic feature of the bottom topography is a linear slope of 4.3 m×2 m delimited by two lateral walls. Since the studied motions are essentially barotropic, homogeneous water was used. Unsheared currents were generated by a simple movement of a wavemaker located in front of the topographic barrier. The conservation of potential vorticity for the currents flowing onto the channel slope produced Rossby waves: reflections at the lateral boundaries then led to the formation of propagating barotropic Rossby normal modes, whose frequencies and spatial structures were selected by the physical system. The currents were measured through the correlation imaging velocimetry (CIV) method, which allowed an extremely detailed synoptic map of the horizontal velocities in an area (13 m²) including the slope to be obtained every 30 s.A variety of experiments were performed in order to provide a complete process study in which the effect of different channel lengths and rotation periods could be tested. Two different lengths of the linear slope, 4.3 and 3.3 m, and rotation periods ranging from 30 to 50 s were considered. The qualitative analysis of the 2D current patterns, and the good agreement found between the measured eigenperiods and the periods obtained by means of a simple analytical model, show that in all cases the first Rossby normal mode was generated. Moreover, numerical simulations based on the shallow-water equations, for a geometry and paddle movements that match closely the experimental setup, allow to calibrate the analytical model and provide useful information on a discrepancy found between experimental and analytical eigenperiods due to an oscillation of the normal mode trajectory.     

Time‐domain response of linear hysteretic systems to deterministic and random excitations

The causal and physically realizable Biot hysteretic model proves to be the simplest linear model able to describe the nearly rate‐independent behaviour of engineering materials. In this paper, the performance of the Biot hysteretic model is analysed and compared with those of the ideal and causal hysteretic models. The Laguerre polynomial approximation (LPA) method, recently proposed for the time‐domain analysis of linear viscoelastic systems, is then summarized and applied to the prediction of the dynamic response of linear hysteretic systems to deterministic and random excitations. The parameters of the LPA model generally need to be computed through numerical integrals; however, when this model is used to approximate the Biot hysteretic model, closed‐form expressions can be found. Effective step‐by‐step procedures are also provided in the paper, which prove to be accurate also for high levels of damping. Finally, the method is applied to the dynamic analysis of a highway embankment excited by deterministic and random ground motions. The results show that in some cases the inaccuracy associated with the use of an equivalent viscous damping model is too large. Copyright © 2005 John Wiley & Sons, Ltd.     

The mass to light ratio and the initial mass function in galactic discs

A low mass-to-light ratio for the baryonic component of spiral galaxies is advocated by a number of dynamical studies and by cosmological simulations of galaxy formation. We discuss the possibility of obtaining low mass-to-light ratios for the stellar component in discs, by changing the Initial Mass Function and the Star Formation History. This revised version was published online in August 2006 with corrections to the Cover Date.     

Evaluation of liquefaction potential in an intermountain Quaternary lacustrine basin (Fucino basin,central Italy)

In this study, we analyse the susceptibility to liquefaction of the Pozzone site, which is located on the northern side of the Fucino lacustrine basin in central Italy. In 1915, this region was struck by a M 7.0 earthquake, which produced widespread coseismic surface effects that were interpreted to be liquefaction-related. However, the interpretation of these phenomena at the Pozzone site is not straightforward. Furthermore, the site is characterized by an abundance of fine-grained sediments, which are not typically found in liquefiable soils. Therefore, in this study, we perform a number of detailed stratigraphic and geotechnical investigations (including continuous-coring borehole, CPTu, SDMT, SPT, and geotechnical laboratory tests) to better interpret these 1915 phenomena and to evaluate the liquefaction potential of a lacustrine environment dominated by fine-grained sedimentation. The upper 18.5 m of the stratigraphic succession comprises fine-grained sediments, including four strata of coarser sediments formed by interbedded layers of sand, silty sand and sandy silt. These strata, which are interpreted to represent the frontal lobes of an alluvial fan system within a lacustrine succession, are highly susceptible to liquefaction. We also find evidence of paleo-liquefaction, dated between 12.1–10.8 and 9.43–9.13 kyrs ago, occurring at depths of 2.1–2.3 m. These data, along with the aforementioned geotechnical analyses, indicate that this site would indeed be liquefiable in a 1915-like earthquake. Although we found a broad agreement among CPTu, DMT and shear wave velocity “simplified procedures” in detecting the liquefaction potential of the Pozzone soil, our results suggest that the use and comparison of different in situ techniques are highly recommended for reliable estimates of the cyclic liquefaction resistance in lacustrine sites characterized by high content of fine-grained soils. In geologic environments similar to the one analysed in this work, where it is difficult to detect liquefiable layers, one can identify sites that are susceptible to liquefaction only by using detailed stratigraphic reconstructions, in situ characterization, and laboratory analyses. This has implications for basic (Level 1) seismic microzonation mapping, which typically relies on the use of empirical evaluations based on geologic maps and pre-existing sub-surface data (i.e., age and type of deposits, prevailing grain size, with particular attention paid to clean sands, and depth of the water table).     

Flow resistance equation for rills

In this paper, a new flow resistance equation for rill flow was deduced applying dimensional analysis and self‐similarity theory. At first, the incomplete self‐similarity hypothesis was used for establishing the flow velocity distribution whose integration gives the theoretical expression of the Darcy–Weisbach friction factor. Then the deduced theoretical resistance equation was tested by some measurements of flow velocity, water depth, cross section area, wetted perimeter, and bed slope carried out in 106 reaches of some rills shaped on an experimental plot. A relationship between the velocity profile, the channel slope, and the flow Froude number was also established. The analysis showed that the Darcy–Weisbach friction factor can be accurately estimated by the proposed theoretical approach based on a power–velocity profile.     

The Barremian carbonate platform strata of the Montenegro Dinarids near Podgorica: a cyclostratigraphic study

High resolution sedimentological analysis of two Lower Cretaceous carbonate platform successions that crop out near Podgorica (southern Dinarides, Montenegro) has resulted in local lithostratigraphic and cyclostratigraphic correlation and the creation of a composite section, about 80 m thick, that includes the Hauterivian/Barremian boundary and almost the whole of the Barremian Stage. The strata studied have been interpreted in terms of depositional environments, recognizing in them a hierarchic cyclic pattern of depositional and early diagenetic features. This cyclic organization is closely comparable to that recorded in other Cretaceous shallow-water successions of the southern Apennines, where the elementary cycles may be grouped in bundles that are in turn grouped into superbundles. This hierarchy has been interpreted to reflect control by climatic oscillations, modulated by the Earth's orbital perturbations. The elementary cycles are related to the precession signal (ca. 20 ky), while the bundles and the superbundles are linked to short (ca. 100 ky) and long eccentricity (ca. 400 ky) respectively. Moreover, these cycles appear to be superimposed on lower frequency Transgressive/Regressive Facies Trends (T/R Facies Trends). Based on superbundles, an orbital chronostratigraphic diagram has been assembled that gives an estimate for the duration of the succession analysed of ca. 4 my.