Raising interest in the interaction between humans and climate drivers to understand the past and current development of floods in urbanised landscapes is of great importance. This study presents a ...regional screening of land-use, rainfall regime and flood dynamics in north-eastern Italy, covering the timeframe 1900-2010. This analysis suggests that, statistically, both climate and land-use have been contributing to a significant increase of the contribution of short duration floods to the increase in the number of flooded locations. The analysis also suggests that interaction arises, determining land-use dynamics to couple with climatic changes influencing the flood aggressiveness simultaneously. Given that it is not possible to control the climatic trend, an effective disaster management clearly needs an integrated approach to land planning and supervision. This research shows that land management and planning should include the investigation of the location of the past and future social and economic drivers for development, as well as past and current climatic trends.
ORC (organic Rankine cycles) represent a sound solution for the exploitation of thermal energy available at low temperature.
The prototype of a small ORC power plant has been realized at the Energy ...Systems Laboratory of Cassino University. In this paper, the plant design, the experimental methodology and the thermodynamic analysis of the work cycle have been illustrated. The aim of the work is to assess the feasibility of small-scale ORC plants.
The basic idea is to analyze the performance of a small ORC plant able to exploit low-temperature heat sources.
Thus, a simple organic Rankine cycle has been analyzed and R245fa as working fluid has been selected. Due to the small working fluid flow rates, a volumetric machine, in particular a scroll expander, has been chosen for mechanical power generation.
The hot source temperature has been varied in the range 75–95 °C and the cold sink temperature ranged between 20 °C and 33 °C. The R245fa vapor maximum pressure varied from 6 up to 10 bar. In this operating range, the best obtained results were: electric power equal to 1.2 kW, specific work about 20 kJ/kg and cycle efficiency slightly greater than 9 percent.
•Few technologies allow exploiting low-temperature thermal energy.•The prototype of a small ORC power plant has been realized.•Parametric analysis of power performance.•The realized pilot plant featured 1 kW output power and a cycle efficiency slightly greater than 9%.
•Analysis of the response of an Alpine catchment to rainfall and snowmelt events.•The selection of pre-event sample can affect hydrograph separation results.•Event water contribution to streamflow is ...higher during large/intense rain events and late snowmelt events.•Distinct runoff generation processes during dry and wet conditions.
Alpine catchments are important sources of fresh water but compared to lower altitude catchments our understanding of the hydrological functioning of these catchments during rainfall and snowmelt events is still limited. The objectives of this study were i) to identify the dominant runoff generation mechanisms in the 0.14-km2 Bridge Creek Catchment in the Italian Dolomites during nine rainfall–runoff events and six snowmelt–runoff events in spring, summer and autumn of 2010–2012; and ii) to assess the effect of the selection of the pre-event water sample on the isotope hydrograph separation results. The isotopic composition of the pre-event water was determined by either a stream water sample taken prior to the event or the average of 19 stream water samples taken during baseflow conditions. The hydrograph separation results for the two methods were very similar for the rainfall events but differed for the snowmelt events. Average event water contributions ranged between 4% and 19% or 2% and 20% of the total runoff during rainfall events, and between 7% and 25% or 9% and 38% during snowmelt events, depending on the method used to determine the isotopic composition of pre-event water. Event water contributions were important during large rainfall events, intense rainfall events and late in the snowmelt season, with maximum event water contributions up to 37% and 46%, depending on the method used for determining the pre-event water composition. The electrical conductivity of stream water tended to first decrease and reach a minimum before peak streamflow and then to increase above pre-event values. The results of this study suggest that during dry conditions, direct channel precipitation and overland flow from the permanently saturated part of the riparian zone dominated the runoff response, with limited contributions of riparian or hillslope groundwater. During wet or very wet conditions (large rainfall events or peak snowmelt), saturation overland flow increased due to the expansion of the saturated areas and riparian groundwater and hillslope subsurface flow to streamflow increased as well. On the one hand, this work contributes to a better understanding of runoff generation processes in mountain headwater catchments where rainfall and snowmelt events dominate the hydrological response. On the other hand, this study highlights the sensitivity of the two-component hydrograph separation technique to the selection of the pre-event water sample for snowmelt events. This calls for further studies in snow-dominated catchments to determine the consistency of the isotopic composition of stream water prior to individual snowmelt events and to assess whether the individual melt events during the melt season should be considered part of a single long snowmelt event.
► Analysis of soil moisture time stability at three depths on two alpine hillslopes. ► Strong temporal stability mainly due to topographic properties. ► High temporal stability also in dry and wet ...periods. ► Validity of ranking stability approach at hillslope scale. ► Structure of soil moisture patterns irrespective of piezometric response triggering.
This paper investigates the temporal stability of near-surface soil moisture at various depths at the hillslope scale. Detailed soil water content data were acquired at 0–6cm, 0–12cm and 0–20cm during three 30-day field campaigns in 2005, 2006 and 2007. Two small alpine hillslopes with relatively homogeneous soil properties and vegetation cover but contrasting morphology were chosen to assess the persistence of spatial organization of soil moisture over time and along the soil profile, to identify the representative sampling locations and to evaluate the temporal stability during wet and dry states.
Results show that both study hillslopes exhibited a strong degree of time stability, as revealed by very high autocorrelation values persisting for several days. The ranking stability approach allowed the identification of sampling locations representative of the average hillslope soil water content. These locations, one for each experimental site, proved to act as good indicators of soil moisture at other depths and even on the other hillslope. The spatial structure of soil moisture fields was not affected by the occurrence of piezometric response and was well preserved at all depths during both wet and dry periods, with a slightly higher degree of temporal stability in dry conditions and for deeper layers. The remarkable persistence of soil moisture spatial patterns over time and along the soil profile on the study sites was mainly related to the macro- and micro-topographic properties of the two hillslopes but the soil wetness conditions generally skewed towards the wet state and the negligible variability of climatic forcing due to the small study scale might have contributed significantly.
The search for the optimal spatial scale for observing landforms to understand physical processes is a fundamental issue in geomorphology. Topographic attributes derived from Digital Terrain Models ...(DTMs) such as slope, curvature and drainage area provide a basis for topographic analyses. The slope–area relationship has been used to distinguish diffusive (hillslope) from linear (valley) processes, and to infer dominant sediment transport processes. In addition, curvature is also useful in distinguishing the dominant landform process. Recent topographic survey techniques such as LiDAR have permitted detailed topographic analysis by providing high-quality DTMs. This study uses LiDAR-derived DTMs with a spatial scale between 1 and 30 m in order to find the optimal scale for observation of dominant landform processes in a headwater basin in the eastern Italian Alps where shallow landsliding and debris flows are dominant. The analysis considered the scaling regimes of local slope versus drainage area, the spatial distribution of curvature, and field observations of channel head locations. The results indicate that: i) hillslope-to-valley transitions in slope–area diagrams become clearer as the DTM grid size decreases due to the better representation of hillslope morphology, and the topographic signature of valley incision by debris flows and landslides is also best displayed with finer DTMs; ii) regarding the channel head distribution in the slope–area diagrams, the scaling regimes of local slope versus drainage area obtained with grid sizes of 1, 3, and 5 m are more consistent with field data; and iii) the use of thresholds of standard deviation of curvature, particularly at the finest grid size, were proven as a useful and objective methodology for recognizing hollows and related channel heads.
Spark-ignition engines are still a competitive solution in a great number of applications. European manufacturers are all involved in the effort of improving fuel economy, at least at some engine ...operating points while meeting, of course, the pollutant emission standards.
The EGR technique, since a long time adopted in reducing the NO
x
formation rate, could be an effective system for fuel economy improvement. Mainly, a de-throttle effect and decreased heat losses to the walls can be obtained in this way. Furthermore, lower exhaust gas temperatures can be reached thus avoiding damages to the noble metals of catalytic converters.
In this paper, the EGR technique has been widely investigated by carrying out an experimental analysis of a small, naturally aspirated, spark-ignition engine. In particular, at full or high load operation, attention has been paid to the combustion development and the influence of EGR rate on the values of spark advance, at knock onset limit, tolerated by the engine has been assessed. Due to lower temperature levels within the combustion chamber, the obtained results show a decreased octane requirement, thus an optimal choice of spark advance is possible. Hence a significant increase of engine efficiency has been obtained.
Quantum measurements using single-photon detectors are opening interesting new perspectives in diverse fields such as remote sensing, quantum cryptography and quantum computing. A particularly ...demanding class of applications relies on the simultaneous detection of correlated single photons. In the visible and near infrared wavelength ranges suitable single-photon detectors do exist. However, low detector quantum efficiency or excessive noise has hampered their mid-infrared (MIR) counterpart. Fast and highly efficient single-photon detectors are thus highly sought after for MIR applications. Here we pave the way to quantum measurements in the MIR by the demonstration of a room temperature coincidence measurement with non-degenerate twin photons at about 3.1 μm. The experiment is based on the spectral translation of MIR radiation into the visible region, by means of efficient up-converter modules. The up-converted pairs are then detected with low-noise silicon avalanche photodiodes without the need for cryogenic cooling.
This study investigates the role of soil moisture on the threshold runoff response in a small headwater catchment in the Italian Alps that is characterised by steep hillslopes and a distinct riparian ...zone. This study focuses on: (i) the threshold soil moisture-runoff relationship and the influence of catchment topography on this relation; (ii) the temporal dynamics of soil moisture, streamflow and groundwater that characterize the catchment's response to rainfall during dry and wet periods; and (iii) the combined effect of antecedent wetness conditions and rainfall amount on hillslope and riparian runoff. Our results highlight the strong control exerted by soil moisture on runoff in this catchment: a sharp threshold exists in the relationship between soil water content and runoff coefficient, streamflow, and hillslope-averaged depth to water table. Low runoff ratios were likely related to the response of the riparian zone, which was almost always close to saturation. High runoff ratios occurred during wet antecedent conditions, when the soil moisture threshold was exceeded. In these cases, subsurface flow was activated on hillslopes, which became a major contributor to runoff. Antecedent wetness conditions also controlled the catchment's response time: during dry periods, streamflow reacted and peaked prior to hillslope soil moisture whereas during wet conditions the opposite occurred. This difference resulted in a hysteretic behaviour in the soil moisture-streamflow relationship. Finally, the influence of antecedent moisture conditions on runoff was also evident in the relation between cumulative rainfall and total stormflow. Small storms during dry conditions produced low stormflow amounts, likely mainly from overland flow from the near saturated riparian zone. Conversely, for rainfall events during wet conditions, higher stormflow values were observed and hillslopes must have contributed to streamflow.
► EGR reduces both knock intensity and exhaust gas temperature with respect to pure air–gasoline fueling. ► Both air–fuel ratio and spark advance can be improved by adopting new boost pressure ...levels. ► Optimizing the main control parameters the power output can be recovered. ► Experimental analyses show that the new control strategy allows increasing fuel economy at the same power output.
Lately, the exhaust gas recycle usage, widely diffused in Diesel engines, has been adopted in SI engines as well. It is a cheap technique which allows a sound control of NO formation meanwhile it can improve engine thermodynamics.
In this paper, the influence of EGR on the operation of a turbocharged spark ignition engine has been evaluated by using both experimental and numerical techniques. In particular, since knock occurrence is a crucial point in the optimization of a turbocharged SI engine, the improvement in knock resistance, at high load operation, has been assessed. First, a method for knock detection and quantification has been illustrated. Then, the influence of EGR on engine performance, octane requirement and exhaust gas temperature was measured at two different rotational speed values and WOT operation.
Since EGR has produced a drop in engine performance (between 10% and 13%) and an increase in knock resistance, a new set of main control variables has been determined in order to restore the original torque level while achieving a significant decrease in specific fuel consumption (between 6% and 11%).
At the end, numerical analyses of engine combustion, aimed to explain the results of experimental investigations, have been carried out and a summary is reported in the paper.
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