Investigating on the occurrence of <i>Paracentrotus lividus</i> in rocky and <i>Posidonia oceanica</i> habitat

The sea urchin Paracentrotus lividus (Lamarck) is the most common grazer in the Mediterranean infralittoral that at high densities overgrazes complex algal assemblages turning them into barren areas. This study has the aim to investigate whether abundance and population structure of P. lividus is consistent between rocky boulders and Posidonia oceanica habitat. At this aim, we have sampled P. lividus at six sites in the Gulf of Alghero (North West Sardinia), 3 fished (sea urchin are harvested) and 3 controls (no harvest is allowed) and at each site the two habitats, 6-10 m deep, were considered. For each combination site x habitat 10 replicates were taken. Density of P. lividus was assessed using quadrats of 1 x 1 m. The size of 20 individual (test diameter without spines) per site was measured by means of a calliper (1#1 0.1mm). Sea urchins, finally were grouped into size classes to examine frequency distributions. Sampling was performed at the end of a harvesting period (April-May 2006). Analyses of data have highlighted a significant variability for both response variables among sites while in Posidonia oceanica habitat a lower density and a higher size were found rather than in rocky habitat. Further data collected at three types of Posidonia oceanica (patches close to rocky habitat, far from rocky habitat and patches bordered by sediment) suggest that the abundance of adults in the seagrass is probably sustained by immigration from the rocky habitat

Predicting the Saturated Hydraulic Conductivity of Clayey Soils and Clayey or Silty Sands

Predictive models able to provide a reliable estimate of hydraulic conductivity can be useful in various geotechnical applications. Since most of the existing predictive methods for saturated hydraulic conductivity estimation are valid only for a limited range of soils or can be applied under certain restrictive conditions, a new method applicable to clayey soils and clayey or silty sands having a wide range of values of soil index properties is proposed in this study. For this purpose, 329 saturated hydraulic conductivity values, obtained by laboratory tests carried out on different soils, were collected in a database and used to develop five equations using a multiple regression approach. Each equation correlates the hydraulic conductivity with one or more geotechnical parameters. An equation was developed that predicts, within an order of magnitude, the saturated hydraulic conductivity in the range from 1.2 × 10−11 to 3.9 × 10−6 m/s, based on simple geotechnical parameters (i.e., clay content, void ratio, plastic limit, and silt content)

Density, planning, and the emergent landscapes of purpose-built student accommodation in England

This mini review explores perspectives on density and discretionary planning policy in relation to the emergent landscapes of purpose-built student accommodation (PBSA) across selected English university cities. It examines the nexus between density in planning policies and transformations in student accommodation, presenting a research gap requiring further investigation. Our research builds upon limited literature on UK PBSA within which there has been inadequate interrogation of policy impacts on the substantial growth of this now mature market sector. By better understanding the relations between national planning policies and their local interpretations regarding PBSA, we can move toward improving understandings for urban futures. The intersectionality between the evolution of the PBSA sector and the planning system are currently underexplored. The paper highlights the proliferation, densification, and concentration patterns of PBSAs and their connections to the surrounding planning system. The emergence of privately developed PBSA in the UK is typically characterized by medium to high rise, and medium to high density development. Higher density PBSA has created a dynamic spectrum of impacts reflecting subjective perceptions of their emergence in university cities. Our mini review illustrates the growth trajectory and direction of the PBSA sector. We conclude with a reflection on the discretionary nature of planning policies for density that often create regulatory loopholes allowing PBSA to thrive as a niche real estate asset class but not necessarily as a local and social collective asset

Spatial competition and efficiency : an investigation in the airport sector

This paper analyses the potential impact of airport competition on technical efficiency by applying the spatial stochastic frontier approach (SSFA) rather than traditional model (SFA). The SSFA allows to isolate the cross-sectional spatial dependence and to evaluate the role of intangible factors in influencing the airport economic performance, through the inclusion of the distance matrix and the shared destinations matrix, calibrated for different distances. By analysing statistical differences between the traditional and the spatial model, it is possible to identify the competition effects. This study includes 206 airports at worldwide level. First, the results show the existence of the spatial component, that could not be otherwise captured by the traditional SFA. Moreover, airport competition is found to affect the efficiency level with either a positive or a negative effect, depending on the distance considered in the spatial model

La Validazione Statistica di test standardizzati di profitto: principali aspetti di metodo e due casi di studio sulla valutazione degli apprendimenti nella scuola primaria

Il lavoro si propone di ripercorrere alcune metodologie generali di analisi dei test per la valutazione degli apprendimenti, discutendo i risultati ottenuti in due casi di studio riguardanti le prove preparate dal Servizio Nazionale di Valutazione (SNV) dell’INVALSI per la classe seconda della scuola primaria. In particolare, viene descritto il processo di analisi dei pre-test attraverso l’utilizzo congiunto degli indicatori derivanti dalla Classical Test Theory e dei modelli di Item Response Theory

On a general extending and constraining procedure for linear iterative methods

Algebraic Reconstruction Techniques (ART), on their both successive or simultaneous formulation, have been developed since early 70's as efficient ''row action methods'' for solving the image reconstruction problem in Computerized Tomography. In this respect, two important development directions were concerned with, firstly their extension to the inconsistent case of the reconstruction problem, and secondly with their combination with constraining strategies, imposed by the particularities of the reconstructed image. In the first part of our paper we introduce extending and constraining procedures for a general iterative method of ART type and we propose a set of sufficient assumptions that ensure the convergence of the corresponding algorithms. As an application of this approach, we prove that Cimmino's simultaneous reflections method satisfies this set of assumptions, and we derive extended and constrained versions for it. Numerical experiments with all these versions are presented on a head phantom widely used in the image reconstruction literature. We also considered hard thresholding constraining used in sparse approximation problems and applied it successfully to a 3D particle image reconstruction problem