毛织物起毛起球的BP神经网络预测研究

采用BP神经网络技术建立和训练反应纱线、织物结构参数与织物起毛起球性之间关系的三层神经网络模型，对比预测值和实验值，表明用神经网络方法预测织物起毛起球性有相当的准确性。     

Improvement of frozen banana (Musa cavendishii, cv. Enana) colour by blanching: relationship between browning, phenols and polyphenol oxidase and peroxidase activities

 Browning in banana (Musa cavendishii, cv. Enana) processed products is a result of phenol oxidation catalysed by polyphenol oxidase (PPO) and peroxidase (POD) or of other non-enzymatic reactions (Maillard and Strecker mechanisms). Microwave and steam blanching significantly reduced PPO and POD activities and phenol levels in banana flesh, steam blanching being the most effective method for enzyme inactivation. Freezing/thawing processes produced a significant increase in phenol levels in all samples, due to cellular breakdown. After microwave heating browning processes occurred while steam-treated samples did not exhibit a significant colour change. Extractable PPO and POD activities in all banana samples increased as a consequence of freezing/thawing: steam-blanched slices exhibited lower residual activities. High correlations occurred between phenols and browning (r=0.86) in control samples. Blanched samples (microwave or steam) only exhibited correlations between PPO (r=0.80) and POD (r=0.80) activities and browning. Received: 22 February 1996     

N-acryloxysuccinimide: Synthesis, characterization, and incorporation in dental adhesives

In an attempt to enrich the world of dentistry through the development of new materials, this study proposes to synthesize and incorporate a monomer containing the N-hydroxysuccinimide (NHS) ester reactive group to a dental adhesive. As such, this study developed a simple method to obtain NHS esters by employing acrylic acid (AA) and NHS in the presence of EDC (N-ethyl-N′-(3-dimethylaminopropyl)carbodiimide), from an aprotic medium. The experimental N-acryloxysuccinimide (NSA) monomer was analyzed by infrared spectroscopy (FTIR) and nuclear magnetic resonance of hydrogen (¹H NMR). This monomer was then incorporated within a prepared dental adhesive, in a 5% proportion. The modified adhesive, containing NSA, was applied to the dental surface of bovine teeth to obtain an adhesive/dentin interface in vitro. The characterization of this interface by Raman spectroscopy presented the formation of new amide bonds. Moreover, through scanning electron microscopy (SEM), it became possible to observe an intense penetration of this modified adhesive on the dental surface. Considering the outcome, it can be concluded that the synthesized NSA monomer provided a favorable condition for the dental adhesives to interact chemically with the dentin collagen fibers.     

Ozone Production in a Dielectric Barrier Discharge with Ultrasonic Irradiation

Ozone production has been investigated using an atmospheric pressure dielectric barrier discharge in pure O₂ at room temperature with and without ultrasonic irradiation. It was driven at a frequency of either 15 kHz or ～40 kHz. The ozone production was highly dependent on the O₂ flow rate and the discharge power. Furthermore, powerful ultrasonic irradiation at a fundamental frequency of ～30 kHz with the sound pressure level of ～150 dB into the discharge can improve the ozone production efficiency, particularly when operated at the frequency of 15 kHz at the flow rate of 15 L/min.     

Hydrogen production by aqueous-phase reforming of glycerol over nickel catalysts supported on CeO2

Nickel catalysts supported on CeO₂ were prepared and evaluated in aqueous-phase reforming of glycerol. Three different methodologies of synthesis were used: wet impregnation, co-precipitation and combustion, and the catalysts were characterized by chemical composition, textural analysis, crystalline structure and reducibility. The reaction was carried out in a batch reactor with solution of 1 and 10 wt.% glycerol, at 523 and 543 K. A maximum glycerol conversion of 30% was achieved by the catalyst prepared by combustion at 543 K using solution 1% glycerol. In the gas phase, the molar fraction of H₂ was always higher than 70% and formation of CH₄ was very low (< 1%). The increase in glycerol concentration decreases the conversion and H₂ formation.     

Monitoring the transesterification reaction with laser spectroscopy

The production of biodiesel is rapidly expanding around the world, making it more important to produce this fuel with more energy efficiency. In this paper, we observed a series of transesterification reactions of soy bean oil and methyl alcohol catalyzed by potassium hydroxide. The observations were made using a non-invasive optical technique. This technique is useful to indicate the endpoint of a transesterification reaction or to determine when this reaction is reaching the state of chemical equilibrium. This study made it possible to improve the follow-up of the transesterification reaction, by optimizing the reaction time with a better monitoring system.     

Continuous production of soybean biodiesel with compressed ethanol in a microtube reactor using carbon dioxide as co-solvent

This work investigates the production of fatty acid ethyl esters (FAEE) from the transesterification of soybean oil in supercritical ethanol in a continuous catalyst-free process using carbon dioxide as co-solvent. The experiments were performed in a microtube reactor in the temperature range of 523 K to 598 K, from 10 MPa to 20 MPa, oil to ethanol molar ratio from 1:20 to 1:40, and co-solvent to substrates mass ratio from 0.05:1 to 0.2:1. Results showed that ethyl esters yield obtained increased with increasing addition of carbon dioxide to the system. Considerable reaction yields were achieved at 598 K, 20 MPa, oil to ethanol molar ratio of 1:20 and using a CO₂ to substrate mass ratio of 0.2:1.     

Proposal of an alternative transmission line model for symmetrical and asymmetrical configurations

This article shows a transmission line model for simulation of fast and slow transients, applied to symmetrical or asymmetrical configurations. A transmission line model is developed based on lumped elements representation and state-space techniques. The proposed methodology represents a practical procedure to model three-phase transmission lines directly in time domain, without the explicit or implicit use of inverse transforms. In three-phase representation, analysis modal techniques are applied to decouple the phases in their respective propagation modes, using a correction procedure to set a real and constant matrix for untransposed lines with or without vertical symmetry plane. The proposed methodology takes into account the frequency-dependent parameters of the line and in order to include this effect in the state matrices, a fitting procedure is applied. To verify the accuracy of the proposed state-space model in frequency domain, a simple methodology is described based on line distributed parameters and transfer function associated with input/output signals of the lumped parameters representation. In addition, this article proposes the use of a fast and robust integration procedure to solve the state equations, enabling transient and steady-state simulations. The results obtained by the proposed methodology are compared with several established transmission line models in EMTP, taking into account an asymmetrical three-phase transmission line. The principal contribution of the proposed methodology is to handle a steady fundamental signal mixed with fast and slow transients, including impulsive and oscillatory behavior, by a practical procedure applied directly in time domain for symmetrical or asymmetrical representations.     

Esterification of Free Fatty Acids Using Layered Carboxylates and Hydroxide Salts as Catalysts

Layered lanthanum and copper(II) laurates were tested as catalysts for methanolic esterification of lauric acid (C₁₂). Factorial design evidenced a positive effect of reaction temperature and amount of catalyst on ester conversion, while the acid:alcohol molar ratio (MR) had a negative effect. With lanthanum laurate, 90.5% conversion was reached at 140???C with 10% catalyst and MR of 6:1. Although the highest conversion with copper(II) laurate converted 81.5% under the same conditions, results were better with a lower amount of catalyst (78% ester at 140???C with 2% catalyst and MR of 6:1). A calcium hydroxide succinate was also investigated showing better catalytic performance than the well-known CaO, under mild reaction conditions (120???C with 1% catalyst and MR of 3:1). Although layered carboxylates can be successively reused, the layered calcium hydroxide salt transformed into inactive CaCO₃ in the second reuse reaction.