Testing a theoretical resistance law for overland flow on a stony hillslope

Overland flow, sediments, and nutrients transported in runoff are important processes involved in soil erosion and water pollution. Modelling transport of sediments and chemicals requires accurate estimates of hydraulic resistance, which is one of the key variables characterizing runoff water depth and velocity. In this paper, a new theoretical power–velocity profile, originally deduced neglecting the impact effect of rainfall, was initially modified for taking into account the effect of rainfall intensity. Then a theoretical flow resistance law was obtained by integration of the new flow velocity distribution. This flow resistance law was tested using field measurements by Nearing for the condition of overland flow under simulated rainfall. Measurements of the Darcy–Weisbach friction factor, corresponding to flow Reynolds number ranging from 48 to 194, were obtained for simulated rainfall with two different rainfall intensity values (59 and 178 mm hr⁻¹). The database, including measurements of flow velocity, water depth, cross-sectional area, wetted perimeter, and bed slope, allowed for calibration of the relationship between the velocity profile parameter Γ, the slope steepness s, and the flow Froude number F, taking also into account the influence of rainfall intensity i. Results yielded the following conclusions: (a) The proposed theoretical flow resistance equation accurately estimated the Darcy–Weisbach friction factor for overland flow under simulated rainfall, (b) the flow resistance increased with rainfall intensity for laminar overland flow, and (c) the mean flow velocity was quasi-independent of the slope gradient.     

Infrared transmission spectroscopy of carbonate samples of biotic origin relevant to Mars exobiological studies

Because it is possible that Mars experienced an ancient climate warmer and wetter than the present one, it is reasonable to suppose that simple forms of life developed there, in the underground or at the surface, as in the terrestrial primitive biosphere. In this work we have performed infrared (IR) transmission spectroscopic analyses directed to examine the reaction to heat treatments of biotic (fresh and fossil materials) and abiotic particulate samples composed of calcium carbonate (aragonite or calcite). The aim is to check if IR spectroscopy can be a useful tool for discriminating between abiotic and biotic (fossil) carbonate samples collected on the martian surface, during in situ or sample-return missions. An important result we found is that, after thermal processing, it is possible to distinguish, by means of IR spectroscopy, abiotic aragonite from aragonite of recent biological origin. In addition we have found that the spectral behaviour of all the analysed fossil samples after heat treatment is the same as that of fresh biotic material irrespective of the original structure (whether aragonite or calcite).     

Statistical properties of dissipation bursts within turbulence: Solar flares and geomagnetic activity

We investigate some statistical properties of the solar soft X-ray flux and of the Auroral Electrojet (AE) index. For both these signals, the probability density functions (PDFs) of normalized differences are shown to display wide, non-Gaussian tails. The shape of the PDFs is nearly unchanged as the timelag, used to calculate differences, varies. Moreover, the two time series are characterized by a power-law distribution for waiting times between successive bursts and by a clear departure from an hypothesis of locally Poisson statistics. A similar behavior is found in a shell model of magnetohydrodynamic (MHD) turbulence.     

Photoelectric lightcurves and rotation periods of the asteroids 46 Hestia and 115 Thyra

Results of photoelectric observations of the asteriods 46 Hestia and 115 Thyra, performed in a cooperative program between the Torino and Table Mountain Observatories, are presented. The rotation periods and the maximum amplitudes are: P_syn = 21^h.0.4 ± 0^h.01, Amplitude = 0.12 mag and P_syn = 7^h.241 ± 0.^h.001, Amplitude = 0.20 mag, for Hestia and Thyra, respectively. The multiple-scattering factors, Q, inferred from the phase relation data are 0.054 ± 0.003 and 0.058 ± 0.002 for Hestia and Thyra, respectively. The low value obtained for Thyra disagrees with the mean one given by Bowell and Lumme (1979, in Asteroids (T. Gehrels, Ed.), pp. 132–169. University of Arizona Press, Tucson) for S-type asteroids.     

Asteroidal binary systems: Detection and formation

Recent occultation data and an analysis of some photometric lightcurves have shown the possible existence of asteroidal binary systems.A simple geometrical model taking into account mutual shadowing effects shows some peculiar features of the lightcurve which can be recovered in several previously observed objects; therefore the hypothesis of a relatively high frequency of binary asteroids should be seriously considered.On the other hand, while the rotational period distribution of large asteroids (D>200 km) is sharply peaked at about 5–8 hours, the surprisingly higher dispersion towards longer periods for intermediate size objects (50<D<150 km) could be connected with a larger probability of binary nature within this class.From a theoretical point of view, the collisional fragmentation of asteroids could originate gravitationally bound fragments, with a tidal transfer of rotational into orbital angular momentum, causing a rapid synchronization of the system. This kind of processes could more easily occur for intermediate objects since: (a) for large ones, very massive colliding bodies are needed for fragmentation, that means a very rare event; (b) for smaller asteroids, solid state interactions are stronger than the gravitational ones, so that a breakage probably causes a complete disruption of the gravitational binding. Further collisional events could disintegrate some systems, so that the present frequency of binary asteroids could be lower than that of the objects whose rotational period was increased by such processes.Paper presented at the European Workshop on Planetary Sciences, organised by the Laboratorio di Astrofisica Spaziale di Frascati, and held between April 23–27, 1979, at the Accademia Nazionale del Lincei in Rome, Italy.     

Groundwater flow analysis using different geothermal constraints: The case study of Acqui Terme area,northwestern Italy

We review some analytical techniques that use underground thermal data as tracers of groundwater flow. These techniques allow the evaluation of the Darcy velocity in shallow aquifers of mid-low permeability and the evaluation of heat gain/loss by conduction in deeper aquifers. Examples of application are then given for the Acqui Terme hydrothermal system, located in the Tertiary Piedmont Basin (northwestern Italy). The analysis of borehole temperatures allowed the inference of the hydraulic features of the sedimentary cover of the hydrothermal system. The results show the presence of a relatively weak flow, with upward and horizontal components, only in conglomerates occurring at the base of the marly impermeable cover. The analysis of the heat transported in the deep parts of the hydrothermal system was approached by splitting the water path into different sections, each with given shape, slope and hydraulic properties. The recharge area is situated in the upland, south of the discharge area. Meteoric water initially descends and then flows horizontally within the fractured metamorphic basement of the basin, heating by conduction. Finally, from a reservoir positioned at intermediate depths, hot water reaches rapidly the surface through a sub-vertical fault. This scheme of deep water flow is constrained by the regional surface heat flow and the local geothermal gradient, and it is consistent with data of rock–water equilibrium temperature.     

Accretion of juvenile crust at the Early Palaeozoic Antarctic margin of Gondwana: geochemical and geochronological evidence from granulite xenoliths

Geodynamic models for the Antarctic sector of the active Early Palaeozoic Palaeo-Pacific margin of Gondwana are based on the nature and age of the deep crust of the Robertson Bay terrane, the outermost lithotectonic unit of the margin. As this crustal block is covered with thick turbidite deposits, the only way to probe the deep crust is through the analysis of granulite xenoliths from Cenozoic scoria cones. Low-K felsic xenoliths yield the oldest (Middle Cambrian) laser-probe U–Pb ages on zircon areas with igneous growth zoning. This finding, along with the positive whole-rock ε_Nd(500Ma), suggests that these felsic rocks derived from a juvenile magma formed during the Early Palaeozoic Ross orogenic cycle. Mafic xenoliths have geochemical-isotopic compositions similar to those of modern primitive island arcs, suggesting the involvement of subducted oceanic crust in their magma genesis and accretion of juvenile crust at the Antarctic margin of Gondwana.     

Lava stones from Neapolitan volcanic districts in the architecture of Campania region,Italy

Results of a research carried out on the lavas from Campi Flegrei and Somma-Vesuvius volcanic districts are reported here. The lavas have been widely employed, since Roman age, in several important monumental buildings of the Campania region, mainly in the town of Naples and in its province. They are classified as trachytes (Campi Flegrei products), tephri-phonolites and phono-tephrites (Somma-Vesuvius complex) from a petrographical point of view. Sampling was carried out from well-known exploitation districts. A substantial chemical difference between the products of the two sectors was confirmed, while petrophysical characterization evidenced similarity among the two different materials, although some differences were recorded even in samples coming from the same exploitation site.     

Uptake of hazardous elements by spring onion (<Emphasis Type="Italic">Allium fistulosum</Emphasis> L.) from soil irrigated with different types of water and possible health risk

Bio-concentration of elements such as Mo, As, Se, Fe, Cu, Zn, Ni and Pb was analyzed in spring onion (Allium fistulosum L.) in three different locations of central Punjab, Pakistan. At location GW, relatively low level of hazardous elements was found in spring onion, suggesting that groundwater is a safe source of water for irrigating food crops. The pH of soil at wastewater irrigation was found less acidic (pH 7.4) than the other sites. The range of concentration in the different samples of spring onion was as follows: 6.15–8.16 mg kg^?1 for Mo, 2.77–4.28 mg kg^?1 for As, 0.395–0.705 mg kg^?1 for Se, 36.73–48.17 mg kg^?1 for Fe, 10.58–16.26 mg kg^?1 for Cu, 28.87–39.79 mg kg^?1 for Zn, 6.66–8.75 mg kg^?1 for Ni and 4.33–6.09 mg kg^?1 for Pb, respectively. High bio-concentration of Zn (15.37) from soil to spring onion was found at canal water irrigated location. The estimated daily intake of metal for spring onion was less, but the health risk index was higher than 1 for Mo, As, Cu, Pb and Ni, respectively. This was due to higher proportion of spring onion in diet, which consequently increased the health risk index for metals. Therefore, it is recommended to avoid growing vegetables in untreated urban and rural wastewater containing elevated amounts of metals.     

Hydraulic failure of diaphragm walls: a possible methodology for safety improvement

The paper presents a methodology aimed at reducing—or even avoiding—the risk of heave and uplift failures of reinforced concrete diaphragm walls. The method is based on the simple concept of increasing the drainage capacity of the embedded portion of the retaining walls. The behaviour of a strutted excavation in a cohesionless soil below groundwater is examined by means of two distinct series of numerical analyses, respectively focused on the hydraulic and mechanical behaviour of the retaining system. It is shown that, for some frequent cases, such methodology is capable to improve the safety of the retaining system with respect to both hydraulic and geotechnical limit states.