Determination of moisture diffusion coefficient in transformer paper using thermogravimetric analysis

This paper presents the methodology used and the results obtained in the determination of moisture diffusion coefficient of non-impregnated transformer insulating paper. In order to establish the diffusion coefficient, drying curves of paper samples were obtained by means of thermogravimetric experiments. The diffusion coefficient parameters were found by applying an optimization process based on genetic algorithms. The error function between measured and simulated curves was determined, and the parameters achieving the best correspondence between measured and estimated values were obtained. As a result, a new equation for the diffusion coefficient of non-impregnated insulating paper is proposed, depending on average moisture concentration, temperature and insulation thickness. The proposed coefficient was validated through experimental cases finding a good agreement between the experimental drying curves and those obtained by simulation using the diffusion coefficient. The proposed diffusion coefficient can be used for the determination of the time required to dry power transformers in factory.     

Nonlinear dynamics of a class-a two-photon laser with injected signal in cascade systems

Abstract

The dynamics of a two-photon laser with injected signal (TPLIS) in the limit of high quality cavity (class-A laser) is analysed by explicitly considering the underlying multi-level structure of the amplifying medium. A three-level cascade system is considered which retains the basic physics of the microscopic lasing processes. In this way the usual two-photon laser equations are consistently modified by the appearance of different dynamic frequency shifts dependent on the two-photon population inversion and on the laser intensity (ac-Stark shift). Although the basic instability scenarios are not qualitatively modified with respect to the effective two-level TPLIS, from the quantitative point of view, population-induced shifts heavily affect the threshold of appearance of instabilities.     

Ethylene production,respiration and gas exchange modelling in modified atmosphere packaging for banana fruits

A mathematical model was developed from experimental measurements to describe the evolution of the O₂, CO₂ and ethylene in a modified atmosphere packaging system for Cavendish bananas. The respiration and ethylene production in the fruits were experimentally obtained from a closed system method and then represented by Michaelis–Menten equations of enzyme kinetics. The gas transfer through the packaging was described by a Fick's diffusion equation, and the temperature dependence was represented based on the Arrhenius law. The model was validated by packaging the fruit in perforated bags of polypropylene and low density polyethylene at 12 °C for a period of 8 days. With the developed model it was possible to satisfactorily describe the experimental evolution of the gas content in the headspace of the packages, obtaining coefficients of determination (R²) of 0.93 for the O₂ levels, 0.90–0.91 for the CO₂ levels, and 0.89–0.93 for the ethylene levels.     

The moderating effect of user experience on satisfaction with electronic banking: empirical evidence from the Spanish case

The aim of this paper is to contribute to the field of satisfaction research from the perspective of electronic banking users—a topic of great interest to financial institutions as they formulate business strategies. In this context, we analyze the possible moderating effect of user experience with the products of a specific institution. A comprehensive review of the scientific literature justified the development of a behavioral model that explains satisfaction using a set of constructs or endogenous variables and the moderating effect of experience. Data was collected from a self-administered Web survey in the authenticated section of the electronic banking service of a prestigious Spanish National financial institution. The analysis tests the relationship between the proposed variables (ease of access, trust, ease of use and usefulness) and demonstrates the moderating effect of electronic banking experience on them. The study was limited to the data of a single financial institution. Caution should therefore be exercised in generalizing the results. The research results provide a number of valuable conclusions for financial institutions. This paper is a pioneer study of satisfaction with electronic banking, especially with regard to the causal relationships between satisfaction and its main determinants.     

Rate-Controlling Mechanisms in the Photo-degradation of 5-Hydroxymethylfurfural

Rate-controlling mechanisms in the photo-degradation of 5-hydroxymethylfurfural (HMF) were studied applying kinetic and thermodynamic compensations. Aqueous solutions of HMF were prepared at a concentration of 100 mg L^?1 and at pH values of 3, 3.4, 4, and 5. The UV irradiation of samples was performed in an installation consisting of a black chamber containing the reactor and a mid-pressure mercury lamp with emission wavelengths between 250 and 740 nm. Every sample was irradiated at 12, 25, 35, and 45 °C for 120 min, analyzing their HMF content each 10 min. The photo-degradation data fitted well to zero-order kinetic model, and the constant values were used to study whether the kinetic and thermodynamic compensation could be applied. The isokinetic temperature was very similar for kinetic compensation (T_B?=?278.0 K) and thermodynamic compensation (T_B?=?277.8 K). Applying the Leffler’s criterion, the HMF photo-degradation was entropically controlled, probably as a consequence of hydrophobic interactions. In order to check the entropical control, two experiments were repeated at pH 3 but avoiding agitation. As the new obtained kinetic constants were highly different from the values previously obtained using agitation, it can be concluded that the HMF photo-degradation is an entropy-controlled process and can be speeded up by changing non-thermal parameters, like agitation.     

Synthesis and characterization of NiPcTSTNa(L) thin films

NiPcTSTNa(L) [L = ethylenediamine (EDA); 1,4-diaminobutane (BDA); and 2,6-diamineanthraquinone (AqDA)] thin films were deposited by thermal evaporation. Their surface morphology was studied by AFM and SEM, and their chemical composition determined by EDS. Optical absorption studies of NiPcTSTNa(L) films were performed in the 200?C1150?nm wavelength range. The optical bandgap of thin films was determined from the (??h ??)^1/2 vs h?? plots for indirect allowed transitions. The temperature dependence of electrical conductivity shows a semiconducting behaviour. The amorphous semiconductor films show thermal activation energies of electrical conduction between 3·3 and 3·7?eV.     

University institutional repositories: competitive environment and their role as communication media of scientific knowledge

Are institutional repositories mere warehouses for digital documents or are they in fact establishing themselves as a rigorous option for the spread of scientific knowledge? This study analyses the competitive environment of the Top100 university repositories, defined as leaders in terms of market participation and penetration. The study also analyses the basic functionalities of preservation and diffusion of academic production through factors related to the prestige of the repositories and of the institutions that operate them. The results show that repositories with a larger digital academic supply are associated with the production of demonstrated scientific rigor.     

Experimental validation of a type-2 fuzzy logic controller for energy management in hybrid electrical vehicles

The aim of this paper is to present experimental validation results of an energy management system for hybrid electrical vehicles based on type-2 fuzzy logic. The energy management system (EMS) is designed by extracting knowledge from several experts using surveys. The consideration of interval type-2 fuzzy sets enables modeling the uncertainty in the answers of the experts. The validation of the EMS is performed on a real-scale heavy duty vehicle equipped with different energy sources such as batteries, fuel cell system and ultracapacitors. Experimental results are strong evidence that type-2 fuzzy logic is wide adapted for performing the energy management in hybrid electrical vehicles.