Optimal experimental design for estimating the kinetic parameters of processes described by the first-order Arrhenius model under linearly increasing temperature profiles

The optimum experimental design for systems following the ®rst-order Arrhenius model under linearly increasing temperature pro®les was studied by determining the sampling conditions that lead to a minimum con®dence region of the model parameters. It was found that experiments should be started at the lowest possible temperature and, for each initial temperature, there is an optimal heating rate. This heating rate is often too high to be feasible, implying that experiments have to be conducted at a lower practicable heating rate. In this situation the experiments should be replicated in order to improve the precision of the estimates. If both the initial temperature and the heating rate are ®xed at their optimal values, the optimal sampling times correspond to fractional concentrations that are irrational numbers (approximately 0.70 and 0.19) whose product is exactly 1=e2, as earlier found for the Bigelow model. A case study based on the estimation of the kinetic parameters of the acid hydrolysis of sucrose is also presente

Application of D-optimal design for determination of the influence of water content on the thermal degradation kinetics of ascorbic acid at low water contents

The kinetics of thermal degradation of ascorbic acid was studied in a Maltodextrin matrix at different temperatures between 7.5 and 140°C. Isothermal experiments were performed with samples earlier equilibrated in environments of known a, at 4°C enclosed in hermetically sealed vials, with water contents (w) between 0.17 and 168g water/g solids. Sampling times were selected according to an optimal experimental design in terms of minimum confidence regions of the parameters estimated, using the Bigelow model and estimates from preliminary experiments. The results showed a quadratic dependence of the reference D-value and linear dependence of the z-value with moisture content: D r(1400C, = 150*07-290*73w+-269w2 (min); z = 12*14+22.99w (“C) and showed the applicability of D-optimal designs for determining kinetic parameters in complex situations, with limited experimental requirements. The dependence of the rate constants with water content could not be described by the WLF model in qualitative terms, although in absolute values this model could be used with constants similar to those expected from glass transition theory. The thermodynamic analysis of the results showed a good application of the compensation theory in the whole range of water contents

Development of active edible coatings for the preservation of Agaricus bisporus mushrooms

Mushrooms are highly perishable food products that tend to lose their unique organoleptic properties immediately after harvest ing. The ir short shelf - life is mainly explained by the high losses of water vapour that favour dehydration, high respiration and microbial colonization by bacteria or fungi. Furthe rmore, enzymatic acti vity and biochemical alteration lead to mushrooms quality losses [1]. The microorganisms most often associated with mushroom spoilage and colonization are gram - negative bacteria e specially those belonging to Pseudomon ae family such as Pseudomonas fluorescens [2]. Active edible coatings h ave been increasingly applied in the last years as an alternative method for the contr ol of microbial contamination in food products. The incorporation of antimicrobial compounds has potential for increasing food quality and safety thus extending its shelf - life [3 - 4]. Recently, several studies have been developed on the incorporation of natural antimicrobial compounds i n edible coatings, responding to an increasing demand by the consumers for foods without chemical additives. Some of the natural antimicrobials are e ssential oils , such as carvacrol and eugenol , which were shown to possess antimicrobial activity against P. f luorescens and E. coli [5]. Aiming at developing an active edible coating to increase the shelf - life of Agaricus bisporus mushrooms p olysaccharide - based coatings were developed using chitosan and alginate , glycerol (as plasticizer) and Tween 80 (as surfactant) . C oating formulations were evaluated through a 2 2 factorial experimental setup with one central point where the influence of the added compounds on W s ( spreading coefficient - wettability) was determined (Pareto charts analyses, p <0.05). W s was evaluated on the pileus of the mushroom once this is the main part of the mushroom and is a indicator of quality and freshness [6]. Tween 80 and polysaccharide concentrations showed to influence the value s of W s . The optimal coating formulation to be a pplied was selected through the determination of the coating that presents the minor value of W s (i.e. value close to zero) and need less quantity of ingredients (i.e. more economic coating) . Based on this, two coatings were selected, one containing 0.5% (w/v) of chitosan, 0. 125% (v/v) of glycerol and 0. 15% (v/v) of T ween 80 and other with 0.5% (w/v) of alginate, 0. 125% (v/v) of glycerol and 0.0 5% (v/v) of T ween 80, presenting W s values of - 62.4 and - 49.9 mN/m, respectively. Different concentrations (0 - 1% v/v) of eugenol and carvacrol and a com bination of both (1:1 – v/v) were incorporated i n chitosan and alginate coatings and their antimicrobial activity was evaluated through CLSI M7 - A7 [7] . I n the case of E. coli , the chitosan - based coatings containing eugenol showed higher antimicrobial activity than th e ones containing carvacrol, being this activity clear after 48 h of incubation . The same behaviour was observed for alginate - based coatings containing eugenol and carvacrol . R esults with P. fluorescens w ere similar to those obtained for E. coli , being the only difference registered for the re sults of inhibition at 24 and 48 h of incubation , w h ere the values of inhibition were similar for both times of incubation. There was a clearly the larger microbial i nhibition against P. fluorescens in comparison to E. c oli , for both coatings - in the presence of eugenol and carvacrol. These results suggest that active polysaccharide - based coatings may present a valuable solution for food packaging in order to prevent microbiological spoilage of Agaricus bisporus mushrooms by P. fluorescens and E. coli . Further studies will be addressed evaluating the effect of developed coatings on shelf - life parameters of Agaricus bisporus mushrooms during storage

Influence of rotation on the electronic states, magnetization and persistent current in 1D quantum ring

Inertial effects can affect several properties of physical systems. In particular, in the context of quantum mechanics, such effects have been studied in diverse contexts. In this paper, starting from the Schr\"{o}dinger equation for a rotating frame, we describe the influence of rotation on the energy levels of a quantum particle constrained to a one-dimensional ring in the presence of a uniform magnetic field. We also investigate how the persistent current and the magnetization in the ring are influenced by temperature and rotating effects

Avaliação experimental de elementos de pequenas dimensões de madeira Câmbala

O presente artigo baseia-se na caracterizar das propriedades fundamentais de um lote de madeira de Câmbala proveniente do Congo. Pretende-se determinar a sua massa volúmica, módulo de elasticidade e tensão de rotura à flexão. Para esse efeito, foram ensaiados 433 provetes de pequenas dimensões à flexão segundo o procedimento preconizado na norma ISO 3133[1], e quantificadas as suas massas volúmicas seguindo as prescrições da norma ISO 3131[2]. Dos resultados experimentais obtidos, constatou-se que os mesmos se situam nos intervalos previstos na bibliografia existente

Neotectónica e períodos de recorrência de grandes sismos e tsunamis na margem SW Ibérica e Golfo de Cádis

Neste trabalho usámos o método numérico das placas finas (Bird, 1999) para modelar a Neotectónica no Golfo de Cadiz e estimar os períodos de recorrência de grandes sismos e tsunamis. Foram testadas várias configurações de falhas e condições fronteira, e os resultados comparados com as observações de GPS, tensão e deformação sísmica. O melhor ajuste às observações é obtido com um modelo que apresenta uma taxa de movimentação de 1 mm/a nos cavalgamentos com orientação E-O e NE-SO, o que corresponde a períodos de recorrência de 1150, 3620 e 9900 anos para sismos de magnitude Mw de 7, 8 e 8.75

Optimal experimental design for estimating the kinetic parameters of processes described by the Weibull probability distribution function

The optimum experimental design for determining the kinetic parameters of the model resulting from the Weibull probability density junction was studied, by defining the sampling conditions that lead to a minimum confidence region of the estimates, for a number of observations equal to the number of parameters. It was found that for one single isothermal experiment the optimum sampling times corresponded always to fractional concentrations that are irrational numbers (approximately 0.70 and 0.19) whose product is exactly l/e’. The experimental determination of the equilibtium conversion (for growth kinetics) is vety important, but in some situations this is not possible, e.g. due to product degradation over the length of time required. Sampling times leading to a maximum precision were determined as a function of the maximum conversion (or yield) attainable. For studies of kinetic parameters over a range of temperatures, performed with a minimum of three isothermal experiments, it was proved that the optimum design consists of two experiments at one limit temperature with two sampling times (those corresponding to fractional concentrations of approximate[v 0.70 and 0.19) and another at the other limit temperature for a sampling time such that the fractional concentration is lie. Case studies are included for clarijication of the concepts and procedures

How banks price loans for LBOs: an empirical analysis of spread determinants

This paper examines which factors determine the pricing of loans for LBOs, using a worldwide sample of 11,111 loans closed in the 2000–2016 period. Our findings are consistent with the hypotheses that loans for LBOs extended to borrowers in market- versus bank-based financial systems are differently priced, and that law and institutional characteristics are important determinants of spreads for deals closed in market-oriented countries. Despite LBO loan pricing differing significantly in normal versus crisis times, loans extended to borrowers in market-based financial systems have higher spreads than those where banks play a major role. Our results also support the hypothesis of tranching as a mechanism of reducing spreads by completing financial markets and mitigating informational asymmetries. Finally, a robust convex relationship between spread and maturity is found, suggesting higher market competition by banks and investors for standard, medium-term maturities.info:eu-repo/semantics/acceptedVersio

Parallel neural network recognition - a multi-agent system approach

This paper presents and discusses the design and the development of a pattern recognition agent based on neural networks. This agent is part of an intelligent navigation system, providing it with the necessary vision abilities so that it can be placed on a strange environment in order to explore and recognise its structures and specificities. Although similar, the properties of the recognised objects change through time and according to each specific environment. The flexibility required by such recognition process was implemented by several pattern recognition agents. Each agent is based on a neural network and can be trained on-line by a parallel training algorithm to allow an effective real time utilisation

Safeguarding cork’s beauty and longevity: innovations in deposition of protective thin films

Cork is a sustainable natural material widely used as a wine stopper. However, some other uses, such as wall coverings, flooring, bags and shoes, face UV damage. To mitigate this issue, we explored the deposition of TiO2 and ZnO thin films via magnetron sputtering on glass and cork substrates. Both films displayed uniformity and the lack of any discernible cracks or voids, remained transparent in the visible region, and offered UV protection. Thus, TiO2 and ZnO blocked UV light with a wavelength of up to 310 nm (Eg = 4 eV) and 370 nm (Eg = 3.3 eV), respectively. Exposure tests, under a sun simulator lamp, revealed that the uncoated cork showed noticeable color changes, even when located under a glass substrate. The TiO2 coating did not prevent cork discoloration, while ZnO prevented it. This study highlights ZnO thin films as a durable solution to safeguard cork materials from UV damage and extend their usability.This research was funded by “the Portuguese Foundation for Science and Technology (FCT) in the framework of the project PTDC/CTM-REF/0155/2020