A Geant4 based engineering tool for Fresnel lenses

Geant4 is a Monte Carlo radiation transport toolkit that is becoming a tool of generalized application in areas such as high-energy physics, nuclear physics, astroparticle physics, or medical physics. Geant4 provides an optical physics process category, allowing the simulation of the production and propagation of light. Its capabilities are well tailored for the simulation of optics systems namely in cosmic-rays experiments based in the detection of Cherenkov and fluorescence light. The use of Geant4 as an engineering tool for the optics design and simulation of Fresnel lens systems is discussed through a specific example.Comment: 4 pages, 6 figures, Proceedings of the 30th ICRC, International Cosmic Ray Conference 2007, M\'erida, M\'exico, 3-11 July 200

Modelling evapotranspiration of soilless cut roses "Red Naomi" based on climatic and crop predictors

Original PaperThis study aimed to estimate the daily crop evapotranspiration (ETc) of soilless cut ‘Red Naomi’ roses, cultivated in a commercial glass greenhouse, using climatic and crop predictors. A multiple stepwise regression technique was applied for estimating ETc using the daily relative humidity, stem leaf area and number of leaves of the bended stems. The model explained 90% of the daily ETc variability (R2 = 0.90, n = 33, P < 0.0001) measured by weighing lysimeters. The mean relative difference between the observed and the estimated daily ETc was 9.1%. The methodology revealed a high accuracy and precision in the estimation of daily ETcinfo:eu-repo/semantics/publishedVersio

Domestic Impact of Internationalisation: The case of JM

The influence of internationalisation processes in the domestic activities of firms’ has not been considered as an important issue in existing models, because they tend to focus on a partial and restricted view of the firm. The purpose of this paper is to challenge that view by attempting a dynamic view of the firm is which primal importance is given to the relationship between international and domestic activities. The main research question is whether domestic activities can be significantly affected by international activities, namely knowledge transfer. Results confirm the dynamic approach adopted by firms however there are no definitive answers in terms of the domestic impact of internationalisation. Despite clear hints of evidence for the internationaldomestic relationship, there was no confirmation of this relationship at the financial level.

Recent progresses in the development of more reliable predictions of average molecular weights and chain-lenght distributions for complex irreversible non-linear polymerizations

Prediction of the structure of branched polymers is a challenging problem, for which only more or less clumsy mathematical solutions have been made available for a long time in the case of kinetically controlled polymerizations. The matter has, nevertheless, considerable economic significance. For instance, a controlled amount of long branching is known to have many benefits on the rheologic properties the widely used polyolefins (Nele et al., 2003). Development of processes and their optimization could benefit a lot with models with better predictive capacities. Progresses in applied mathematics could at last bring about a considerable improvement in this situation. This paper reviews recent methods (Costa and Dias, 2003; Dias and Costa, 2003, 2005) allowing the direct computation of moments (i. e. avoiding Hulburt-Katz closures) of polymer chain length distributions, even in the presence of gel, overcoming past difficulties in their computational implementation. Description of non-linear free radical polymerizations is now possible, thanks to the development methods for solving highly stiff two point boundary value problems (Cash et. al., 2001). Chain length distributions are obtained by adapting algorithms better known with Laplace transform inversion (Papoulis, 1956; Weeks, 1966; Durbin, 1974). Numerous past inconsistencies leading to unwanted errors are now avoided through the use of well-founded chemical and mathematical principles

520b Dynamic prediction of microstructure and molecular size in coordination terpolymerizations including cross-linking and branching

The production of terpolymers using coordination catalysts is a subject with a great industrial importance, being the ethylene-propylene-diene (EPDM) the most representative chemical system within this class of polymers[1-4]. For technical reasons, only a very low content (less than 2 mol %) of diene monomer (such as ethylidene norbornene (ENB)) can usually be incorporated in the terpopolymer. Chain branching and cross-linking, leading eventually to gel formation are important limiting factors to increase the diene content as desired to obtain products with improved properties.FCT European Communit

Semibatch operation and primary cyclization effects in homogeneous free-radical crosslinking copolymerizations

A theoretical analysis is presented on the use of semibatch reactors for producing non-linear copolymers through the homogeneous free-radical polymerization of mono- and divinyl-monomers. The kinetic scheme distinguishes two kinds of pendant double bonds and five kinds of polymer radicals, as it also takes into account the primary cyclization of terminal divinyl units. In spite of the fairly large number of groups and reactions, the generating function of vector chain length distribution of polymer species can still be accurately computed by a numerical implementation of the method of characteristics and thus average molecular weights before and after gelation can be reliably obtained. The influence of feed policies of the monomers, initiator and transfer agent on gelation, average chain lengths and weight fraction of sol is discussed, as well as their sensitivity to some kinetic parameters

Overcoming performance and convergence issues of discrete transform based modeling of crosslinking classical and reversible deactivated radical polymerizations

Population balances of polymer species in terms 'of discrete transforms with respect to counts of groups lead to tractable first order partial differential equations when ali rate constants are independent of chain length and loop formation is negligible [l]. Average molecular weights in the absence ofgelation are long known to be readily found through integration of an initial value problem. The extension to size distribution prediction is also feasible, but its performance is often lower to the one provided by methods based upon real chain length domain [2]. Moreover, the absence ofagood starting procedure and a higher numerical sensitivity hás decisively impaired its application to non-linear reversibly deactivated polymerizations, namely NMRP [3].This work was financially supported by: Project POCI-01-0145-FEDER-006984 – Associated Laboratory LSRE/LCM funded by FEDER funds through COMPETE2020 - Programa Operacional Competitividade e Internacionalização (POCI)