172,251 research outputs found
Overland flow generation on hillslopes of complex topography: Analytical Solutions
No full textThe analytical solution of the overland flow equations developed by Agnese et al. (2001; Hydrological Processes 15:
3225–3238) for rectangular straight hillslopes was extended to convergent and divergent surfaces and to concave and convex
profiles. Towards this aim, the conical convergent and divergent surfaces are approximated by a trapezoidal shape, and the
overland flow is assumed to be always one-dimensional. A simple ‘shape factor’ accounting for both planform geometry
and profile shape was introduced: for each planform geometry, a brachistochrone profile was obtained by minimizing a
functional containing a slope function of the profile. Minima shape factors are associated with brachistochrones; interestingly,
brachistochrones associated with rectangular surfaces have a simple power-law form. For a fixed profile shape, the rapidness of
overland flow increases with the degree of divergence; for a fixed planform geometry, however, the overland flow associated
with convex profiles is more rapid than that associated with concave profiles. An extended analytical solution is also proposed
for the instantaneous response function
Modelling wet and dry spells for daily rainfall data series: an application to irrigation management in North-West Italy
No full textRainfall time variability is relevant for agricultural production. The daily time scale is often used in modelling crop and soil water balance. In this work a novel statistical analysis of wet and dry spells is presented, together with an application in an Italian area characterised by a relevant climate spatial variability, due to the presence of both high mountains (e.g.: Mont Blanc) and of the Mediterranean Sea. Statistical analysis of the sequences of rainy days, wet spells (WS), and that of no-rainy days, dry spells (DS), could be carried out separately (as widely applied in the past) or jointly, by introducing the inter-arrival time (IT), representing the time elapsed between two subsequent rainy days. Investigating on daily rainfall data series recorded in Sicily, Agnese et al. (2014) found that IT statistics can be described by the 3-parameter Lerch distribution; in turn, WS and DS distributions can be easily derived from IT distribution. Alternatively, the knowledge of both WS and DS distributions allow deriving IT distribution; in this case, WScan be described by the well-accepted geometric distribution, whereas the 2-parameter polylogarithm distribution can be used for DS, as recently suggested (Agnese et al., 2012) in place of the previously used 1-parameter logarithmic distribution (Chatfield, 1966). In this work, by using some daily rainfall data series recorded in Alpine and Sub-Alpine Areas, the equivalence between the above-mentioned approaches is showed. Furthermore, some interesting relationships between respective parameters are also illustrated. A simple soil water model is then used, using this rainfall statistical model, in order to evaluate the irrigation efficiency as a consequence of variations in the timing of surface irrigation, following the approach described in the paper of Canone et al. (2015)
Determinazione del contenuto energetico delle precipitazioni tipiche dell'ambiente mediterraneo
No full textA model of dunnian flow at hillslope scale
No full textThe development of a thin stream above the soil surface (overland flow) is associated to two mechanism of runoff generation on the hillslope: the infiltration excess (hortonian flow) and saturation excess (dunnian flow) mechanism. The first one is typical of arid and semi-arid regions, usually characterised by high rainfall intensities on soil exhibiting low permeability. The second one, firstly introduced by Hewlett and Hibbert, constitutes the main mechanism of runoff generation in humid regions, characterised by high groundwater table. In the last mechanism runoff is produced by contributing areas of restricted extent that expands with time, where near to the bottom of the hillslope a high value initial soil water content occurs and gradually decreases versus upstream of the hillslope. Following this sketch, under the hypothesis of constant depth of the permeable layer, for stationary rainfall of indefinite duration, this work aims to investigate on the implications of temporal variability of active hillslope length on the hydrologic response for the dunnian mechanism of runoff generation.
The flow in the unsaturated zone is modelled by the piston displacement model of Beven (1982a, 1982b). Once the wetting front reaches the impermeable layer (with different times along the hillslope), the transportation process, over and under the hillslope, is represented as the envelope of the infinite sequence of hydrographs, corresponding to the progressive lengths activated by the infiltration process and Ta - shifted from the beginning of the rainfall, where Ta is the starting up time associated to the active length. The overland hydrographs are modelled with the analytical solution of Agnese et al. (2001) over a plan hillslope, recently introduced. The subsurface stormflow hydrographs is modelled by using the classical linear storage model
Analisi della tendenza climatica dell'evapotraspirazione nel territorio siciliano
No full textLong effective evapotranspiration (E) series was derived from the longest temperature series available in Sicily. The regional trend analysis performed has shown a slight upward trend of E
STIMA DELLA RADIAZIONE SOLARE GIORNALIERA IN SICILIA MEDIANTE I DATI DI TEMPERATURA MASSIMA E MINIMA
No full textBy using thermometric data series from 36 sicilian stations , the authors use different relationship for indirect determination of daily solar radiation. The best performance was given by Hargreaves-Samani formula which is then parameterized by the authors for the investigated region
Possibili modificazioni delle componenti del bilancio idrologico indotte dalle variazioni climatiche
No full textChanges in polyamines, c-myc and c-fos gene expression in osteoblast-like cells exposed to pulsed electromagnetic fields
No full textPulsed electromagnetic field (PEMF) stimulation promotes the healing of fractures in humans,
though its effect is little known. The processes of tissue repair include protein synthesis and cell
differentiation. The polyamines (PA) are compounds playing a relevant role in both protein synthesis
processes and cell differentiation through c-myc and c-fos gene activation. Since several studies have
demonstrated that PEMF acts on embryonic bone cells, human osteoblast-like cells and osteosarcoma
TE-85 cell line, in this study we analyzed the effect on cell PAs, proliferation, and c-myc and c-fos gene
expression of MG-63 human osteoblast-like cell cultures exposed to a clinically useful PEMF.
The cells were grown in medium with 0.5 or 10% fetal calf serum (FCS). c-myc and c-fos gene expressions
were determined by RT-PCR. Putrescine (PUT), spermidine (SPD), or spermine (SPM)
levels were evaluated by HPLC. [3H]-thymidine was added to cultures for DNA analysis. The PEMF
increased [3H]-thymidine incorporation (P..01), while PUT decreased after treatment (P..01);
SPM and SPD were not significantly affected. c-myc was activated after 1 h and downregulated
thereafter, while c-fos mRNA levels increased after 0.5 h and then decreased. PUT, SPD, SPM trends,
and [3H]-thymidine incorporation were significantly related toPEMFtreatment. These results indicate
that exposure to PEMF exerts biological effects on the intracellular PUT of MG-63 cells and DNA
synthesis, influencing the genes encoding c-myc and c-fos gene expression. These observations
provide evidence that in vitro PEMF affects the mechanisms involved in cell proliferation and
differentiation
Sulla possibilità di estendere l'informazione climatica del passato attraverso le serie dendrocronologiche
No full textE’ noto che, a parte alcune eccezioni, la misura sistematica delle variabili meteorologiche in Italia ha avuto inizio a metà del XIX secolo. Non diversamente, in Sicilia si dispone di un numero limitato di serie storiche pluviometriche di consistenza pari a 100-120 anni e termometriche di 60-70 anni. L’obiettivo di una più approfondita conoscenza del clima passato, in Sicilia, può essere perseguito estendendo alcune serie storiche climatiche disponibili, mediante la dendroclimatologia, scienza che permette, attraverso l’analisi degli anelli annuali di accrescimento degli alberi, di legare
l’entità di tale accrescimento alle cause che lo hanno generato e, in particolare, alle condizioni climatiche corrispondenti. Lo studio è stato condotto nel territorio di Linguaglossa (CT), sulle pendici dell’Etna, in cui sono disponibili serie storiche abbastanza lunghe e complete sia di piogge sia di temperature e sono presenti alberi secolari di Pino laricio
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