State observer with Round-Robin aperiodic sampled measurements with jitter

A sampled-data observer is proposed for linear continuous-time systems whose outputs are sequentially sampled via non-uniform sampling intervals repeating a prescribed Round-Robin sequence. With constant sampling intervals (jitter-free case) we provide constructive necessary and sufficient conditions for the design of an asymptotic continuous–discrete observer whose estimation error is input-to-state stable (ISS) from process disturbances and measurement noise. We use a time-varying gain depending on the elapsed time since the last measurement. With non-constant sampling intervals (jitter-tolerant case), our design conditions are only sufficient. A suspension system example shows the effectiveness of the proposed approach

Hybrid Propulsion Efficiency Increment through Exhaust Energy Recovery—Part 2: Numerical Simulation Results

The efficiency of hybrid electric vehicles may be substantially increased if the energy of exhaust gases, which do not complete the expansion inside the cylinder of the internal combustion engine, is efficiently recovered using a properly designed turbo-generator and employed for vehicle propulsion. Previous studies, carried out by the same authors of this work, showed a potential hybrid vehicle fuel efficiency increment up to 15% employing a 20 kW turbine on a 100 HP-rated power thermal unit. The innovative thermal unit proposed here is composed of a supercharged engine endowed with a properly designed turbo-generator, which comprises two fundamental elements: an exhaust gas turbine expressly designed and optimized for the application, and a suitable electric generator necessary to convert the recovered energy into electric energy, which can be stored in the on-board energy storage system of the vehicle. In this two-part work, the realistic efficiency of the innovative thermal unit for hybrid vehicles is evaluated and compared to a traditional turbocharged engine. In Part 1, the authors presented a model for the prediction of the efficiency of a dedicated radial turbine, based on a simple but effective mean-line approach; the same paper also reports a design algorithm, which, thanks to some assumptions and approximations, allows fast determination of the right turbine geometry for a given design operating condition. It is worth pointing out that, being optimized for quasi-steady power production, the exhaust gas turbine here considered is quite different from the ones commonly employed for turbocharging applications; for this reason, and in consideration of the required power size, such a turbine is not available on the market, nor has its development been previously carried out in the scientific literature. In this paper, Part 2, a radial turbine geometry is defined for the thermal unit previously calculated, employing the design algorithm described in Part 1; the realistic energetic advantages that could be achieved by the implementation of the turbo-generator on a hybrid propulsion system are evaluated through the performance prediction model under different operating conditions of the thermal unit. As an overall result, it was estimated that, compared to a reference traditional turbocharged engine, the turbo-compound system could gain vehicle efficiency improvement between 3.1% and 17.9%, according to the output power delivered, with an average efficiency increment of 10.9% evaluated on the whole operating range

Hybrid Propulsion Efficiency Increment through Exhaust Energy Recovery—Part 1: Radial Turbine Modelling and Design

The efficiency of Hybrid Electric Vehicles (HEVs) may be substantially increased if the energy of the exhaust gases, which do not complete the expansion inside the cylinder of the internal combustion engine, is efficiently recovered by means of a properly designed turbogenerator and employed for vehicle propulsion; previous studies, carried out by the same authors of this work, showed a potential hybrid vehicle fuel efficiency increment up to 15% by employing a 20 kW turbine on a 100 HP rated power thermal unit. The innovative thermal unit here proposed is composed of a supercharged engine endowed with a properly designed turbogenerator, which comprises two fundamental elements: an exhaust gas turbine expressly designed and optimized for the application, and a suitable electric generator necessary to convert the recovered energy into electric energy, which can be stored in the on-board energy storage system of the vehicle. In these two parts, the realistic efficiency of the innovative thermal unit for hybrid vehicle is evaluated and compared to a traditional turbocharged engine. In Part 1, the authors present a model for the prediction of the efficiency of a dedicated radial turbine, based on a simple but effective mean-line approach; the same paper also reports a design algorithm, which, owing to some assumptions and approximations, allows a fast determination of the proper turbine geometry for a given design operating condition. It is worth pointing out that, being optimized for quasi-steady power production, the exhaust gas turbine considered is quite different from the ones commonly employed for turbocharging application; for this reason, and in consideration of the required power size, such a turbine is not available on the market, nor has its development been previously carried out in the scientific literature. In the Part 2 paper, a radial turbine geometry is defined for the thermal unit previously calculated, employing the design algorithm described in Part 1; the realistic energetic advantage that could be achieved by the implementation of the turbogenerator on a hybrid propulsion system is evaluated through the performance prediction model under the different operating conditions of the thermal unit. As an overall result, it was estimated that, compared to a reference traditional turbocharged engine, the turbocompound system could gain vehicle efficiency improvement between 3.1% and 17.9%, depending on the output power level, while an average efficiency increment of 10.9% was determined for the whole operating range

Linee guida per la valutazione della resilienza delle foreste Mediterranee ai cambiamenti climatici [Guidelines for assessing the resilience of Mediterranean forests to climate change]

We have defined optimal management models for improving or strengthening the resilience of forest environments: in particular, five best management practices aiming at improving the Mediterranean forests resilience with reference to the desertification risk. The 5 Best ManagementPractices are: BMP1 - Actions favoring mixing of species and hydrogeological stability of forests; BMP2 - Renaturalization of forest plantations; BMP3 - Remedial measures and restoration of degraded forests; BMP4 - Actions aimed at enhancing complex structural forests; BMP5 - Actions favoring connectivity in agro-forestry systems. The best management practices have been then applied adapting them to 16 different intervention types and they have been tested on 10 regional forest categories on an overall surface of 120 hectares. The intervention areas make up a set of testing areas according to the different intervention types carried out. Finally, we have defined the forest resilience Assessment Chart. The Chart has been worked out to improve the sylviculturist\u2019s intervention assessment in order to grant a proper application of the forest resilience intervention practices. This chart includes 10 questions on parameters having an influence on the resilience and on the forest adaptation capacity to climate changes. The parameters are: current and dynamic Forest Category; Specific tree Composition; Vegetation Layers covering; Forest vertical structure; Forest horizontal structure; Dendrometric parameters; Species indicating disturbance; Ground cover; Regeneration; Internal and external steadiness

Optimizing the Sampling Area across an Old-Growth Forest via UAV-Borne Laser Scanning, GNSS, and Radial Surveying

Aboveground biomass, volume, and basal area are among the most important structural attributes in forestry. Direct measurements are cost-intensive and time-consuming, especially for old-growth forests exhibiting a complex structure over a rugged topography. We defined a methodology to optimize the plot size and the (total) sampling area, allowing for structural attributes with a tolerable error to be estimated. The plot size was assessed by analyzing the semivariogram of a CHM model derived via UAV laser scanning, while the sampling area was based on the calculation of the absolute relative error as a function of allometric relationships. The allometric relationships allowed the structural attributes from trees’ height to be derived. The validation was based on the positioning of a number of trees via total station and GNSS surveys. Since high trees occlude the GNSS signal transmission, a strategy to facilitate the positioning was to fix the solution using the GLONASS constellation alone (showing the highest visibility during the survey), and then using the GPS constellation to increase the position accuracy (up to PDOP~5−10). The tree heights estimated via UAV laser scanning were strongly correlated (r2 = 0.98, RMSE = 2.80 m) with those measured in situ. Assuming a maximum absolute relative error in the estimation of the structural attribute (20% within this work), the proposed methodology allowed the portion of the forest surface (≤60%) to be sampled to be quantified to obtain a low average error in the calculation of the above mentioned structural attributes (≤13

Close-to-Nature Silviculture to Maintain a Relict Population of White Oak on Etna Volcano (Sicily, Italy): Preliminary Results of a Peculiar Case Study

Habitat loss is a potential long-term effect of projected climate change for Mediterranean forest ecosystems. Here, we investigated the effectiveness of a close-to-nature silvicultural practice to conserve an old-growth white oak forest patch in Sicily (Italy) and promote regeneration dynamics. The study area, although small, is distinctive for its isolation, position and environmental characteristics. We conducted a Before-After Control-Impact (BACI) study to analyse the responses of different taxonomic groups (vascular plants and birds) to silvicultural treatments (selection thinning, no thinning), and to determine whether close-to-nature silviculture practices may cause significant shifts in the investigated communities. Specifically, we assessed the responses of (1) vascular plants by means of species diversity and taxonomic distinctness indices and (2) birds in terms of diversity, abundance and forest specialisation. Preliminary results suggest that cautious close-to-nature silviculture practice could-by mimicking natural gap dynamics-contribute to maintaining old-growth forest patches and promote oak seedling emergence without short-term detrimental impacts on biodiversity. Although the monitoring has to be repeated over the long-term, the multi-taxon approach and indices incorporating information on taxonomic relationships into diversity measures were demonstrated to be valuable tools for interpreting biotic community structure and dynamics

The evolution in time of the concept of fast growing tree species: is it possible to use a definition applicable to all environmental conditions?

Although the expression “fast-growing species” (FGS) referred to tree species has been since long time used, a clear definition has not been adopted for decades. Starting from the Italian historical background, we searched for the definitions of FGS formulated over time at a national and international level. The mean annual increment (MAI) of 10 m3 ha-1, identified by the FAO, has been the most commonly considered threshold until recently. Subsequently, experimental activities and research efforts have consistently enhanced the productivity of FGS, and other definitions have been proposed accordingly. Hence, FGS should provide annual wood yields of 15-25 m3 ha-1 with rotations of less than 25-30 years. In Europe, the maximum MAI can reach about 20-25 m3 ha-1, while in fast-growing tropical plantations the MAI frequently exceeds 30-35 m3 ha-1. However, we deem that the threshold of 10 m3 ha-1 year-1 is still reliable for Mediterranean conditions. Since the fast-growing is a relative concept, strongly affected by species’ traits, environmental conditions and cultural practices, a future increase in the productivity levels of wood plantations can be expected

A case study of the application of hand-held mobile laser scanning in the planning of an Italian forest (Alpe Di Catenaia, Tuscany)

Precision forestry is becoming a key sector for forest planning because it allows complex analyses of forest data to be carried out simply and economically. It contributes to the integration between technicians and operators in the sector by guaranteeing the transparency of the forest management operations (Corona et al., 2017). In the context of the progressive development of technology, we investigated the feasibility of using the hand-held mobile laser scanner (HMLS) system in different types of forest sites and comparison of the characteristics of individual trees (tree height, diameters at breast height) with traditional surveys, applied with the aim to validate the performance of the system for a future alternative methodology for forest planning thanks to the collaboration with the forestry company “Dimensione Ricerca Ecologia Ambiente Italia” (D.R.E.Am. Italia). GEOSLAM ZEB HORIZON ™ laser scanner is a hand-held mobile laser scanner containing SLAM technology that can be solved the problem of no GNSS signal or poor signal under the forest canopy making it more practical for forest investigations (Gollob et al., 2020). 15 forest sample plots are selected to reflect different stand conditions in Mediterranean forests taking into count the development stage and density of the sub-canopy vegetation, as well as the species composition in the forest stands. The aim of this study is to show the possible extrinsic circumstances that make the method fail by varying the ecological status of forest plots

The evolution in time of the concept of fast growing tree species: is it possible to use a definition applicable to all environmental conditions?

Although the expression \u201cfast-growing species\u201d (FGS) referred to tree species has been since long time used, a clear definition has not been adopted for decades. Starting from the Italian historical background, we searched for the definitions of FGS formulated over time at a national and international level. The mean annual increment (MAI) of 10 m3 ha-1, identified by the FAO, has been the most commonly considered threshold until recently. Subsequently, experimental activities and research efforts have consistently enhanced the productivity of FGS, and other definitions have been proposed accordingly. Hence, FGS should provide annual wood yields of 15-25 m3 ha-1 with rotations of less than 25-30 years. In Europe, the maximum MAI can reach about 20-25 m3 ha-1, while in fast-growing tropical plantations the MAI frequently exceeds 30-35 m3 ha-1. However, we deem that the threshold of 10 m3 ha-1 year-1 is still reliable for Mediterranean conditions. Since the fast-growing is a relative concept, strongly affected by species\u2019 traits, environmental conditions and cultural practices, a future increase in the productivity levels of wood plantations can be expected

Which are Southern Italy’s fastest growing tree species? Lessons from the past for future perspectives, with a special focus on Sicily

Fast growing tree species can generate high wood production in a short time frame. However, maximum productivity is dependent on environmental and management conditions as well as intrinsic plant traits. Within this framework, our research was into tree species with the highest Mean Annual Increments (MAIs) in southern Italy, particularly in Sicily. Eucalyptus spp., Acacia saligna (Labill.) H. L. Wendl., Ailanthus altissima Mill. (Swingle), Pinus halepensis Mill. (including Pinus brutia Ten.), Pinus canariensis C.Sm. and Pinus radiata D. Don. were identified. In particularly suitable conditions, the MAI of eucalypt coppices ranged from 8 to 12 m3 ha-1, and from 13 to 19 m3 ha-1, in Eucalyptus camaldulensis Dehnh. and Eucalyptus globulus Labill., respectively. The MAI of E. camaldulensis high forests was slightly over 6 m3 ha-1, while that of E. globulus high forests was very similar to its coppice value. Considering the preliminary data, Acacia saligna Labill. H. L. Wendl. can achieve good wood production. Pinus halepensis Mill. and Pinus brutia (Ten.) Holmboe achieved MAIs of 5-7 m3 ha-1. Other species may be promising but either data is very limited or their invasive potential requires careful consideration. This historical review has shown that with optimal tree species-planting site-cultivation technique combinations, tree species can achieve wood yields typical of fast-growing species in Mediterranean Italy, too