Search results for " modelling"
showing 10 items of 1055 documents
Predicting the equilibrium bed slope in natural streams using a stochastic model for incipient sediment motion
2011
In this paper, a method to predict the equilibrium bed slope in natural streams based on the incipient motion criterion is proposed. The method is based on the criterion suggested by Gessler to simulate the grain size distribution of the armour coat using the concept of critical shear stress of a sediment mixture. In particular, a different expression of the probability for a single particle size to be part of the armour coat is firstly proposed; then, a simple two-steps criterion is suggested to estimate the safety factor required by the proposed approach. The method is applied in three different Italian regions (Calabria, Basilicata, and Tuscany) and required several field campaigns invol…
Pressure Retarded Osmosis: a Membrane Process for Environmental Sustainability
2016
Salinity Gradient Power (SGP) based on the controlled mixing between two solutions at different salinities is a viable alternative to produce power from renewable sources. Pressure Retarded Osmosis (PRO) is one of the most promising technologies proposed so far for the exploitation of such energy source. Apart from the typical source of salinity gradients, namely river water and seawater, more and more interest has been raised recently towards the use of non-conventional saline solutions. In this work, water originating from a sewage treatment plant is used as the dilute solution (feed solution), while brine exiting from a desalination plant is used as the concentrate (draw solution), thus …
Kindergarten teachers adjust their teaching practices in accordance with children's academic pre-skills
2011
This study examined the extent to which kindergarten children’s academic pre‐skills are associated with their teachers’ subsequent teaching practices. The pre‐skills in reading and math of 1268 children (655 boys, 613 girls) were measured in kindergarten in the fall. A pair of trained observers used the Classroom Assessment Scoring System instrument to observe 49 kindergarten teachers on their emotional support, classroom organisation and instructional support in kindergarten in the spring. The results of the multilevel modelling showed that low levels of academic pre‐skills in kindergarten classrooms in the fall predicted high classroom quality in the classrooms later on. The results sugge…
Factors behind low reading literacy achievement
2004
The initial results of the Programme for International Student Assessment (PISA) indicated that Finnish and Swedish students are among the best readers in all OECD countries. However, the literac ...
Upper Secondary School and University Level Students’ Perceptions of Extractions in Context: Experiences from a Simple Laboratory Experiment
2021
We discuss the pedagogical challenges associated with the current way of introducing extraction in upper secondary school chemistry education. These challenges were identified based on a survey of upper secondary school textbooks and verified through a questionnaire study. To address the identified challenges, we introduce a simple and effective extraction experiment which focuses on building a deeper conceptual understanding of extraction processes. The operationally simple extraction experiment and the accompanying questionnaire revealed that while students have several chemical misconceptions arising from the use of superficial everyday examples, they have all the necessary knowledge for…
SINGLE FACTOR STOCHASTIC MODELS WITH SEASONALITY APPLIED TO UNDERLYING WEATHER DERIVATIVES VARIABLES
2003
This paper estimates single factor stochastic models describing daily air temperature behaviour. We modify classical financial models to reflect temperature seasonality and fit them to a time series representing temperatures in Spain. The estimated models are used in Montecarlo simulations to obtain heating and cooling degree-days, which are used as an underlying reference in weather derivatives. The final goal of this work is to obtain an insight into weather derivative valuation, and so making it easier to manage economic activity risks closely related to temperature (i.e. oil, gas and electricity prices and volumes). En este trabajo se estiman modelos estocásticos unifactoriales que desc…
An integrated fuzzy-stochastic model for revenue management: The hospitality industry case
2016
Revenue management aims at improving the performance of an organization by selling the right product/service to the right customer at the right time. This task is very dependent on uncontrollable external factors. In the hospitality industry, rooms of the hotel represent perishable assets and fixed capacities at the same time. Therefore, in the case of a stochastic process for customers calling in reservations prior to a particular booking date, a common problem for hotels is to devise a policy for maximizing the total expected profit conditional on the set of bookings. We propose a fuzzy model for the hotel revenue management under an uncertain and vague environment. Fuzziness of objectiv…
Stochastic Fatigue Models for Efficient Planning Inspections in Service of Aircraft Structures
2008
For important fatigue-sensitive structures of aircraft whose breakdowns cause serious accidents, it is required to keep their reliability extremely high. In this paper, we discuss inspection strategies for such important structures against fatigue failure. The focus is on the case when there are fatiguecracks unexpectedly detected in a fleet of aircraft within a warranty period (prior to the first inspection). The paper examines this case and proposes stochastic models for prediction of fatigue-crack growth to determine appropriate inspections intervals. We also do not assume known parameters of the underlying distributions, and the estimation of that is incorporated into the analysis and d…
A model of the filling process of an intermittent distribution network
2010
In many countries, private tanks are acquired by users to reduce their vulnerability to intermittent supply. The presence of these local reservoirs modifies the user demand pattern and usually increases user water demand at the beginning of the service period depending on the tank filling process. This practice is thus responsible for the inequality that occurs among users: those located in advantaged positions of the network are able to obtain water resources soon after the service period begins, while disadvantaged users have to wait much longer, after the network is full. This dynamic process requires the development of ad hoc models in order to obtain reliable results. This paper discus…
DEVELOPMENT OF AN OLIVE PHENOLOGICAL MODEL IN RELATION TO AIR TEMPERATURE
2008
The effect of air temperature on olive phenological development has not been extensively studied. Indirectly related data are available, mostly from air pollen concentration measurements rather than direct observation of phenological stages. Data on phenological stages of olive collected in Sicily, by the Sicilian Agrometeorological Service (SIAS), in 10 locations characterized by different climatic conditions were used to develop and calibrate a phenological model for the most important developmental stages in olive. Phenological stages under study were: bud break, inflorescence emission, and full bloom A base-temperature linear model was developed by choosing a temperature threshold using…