Determination of dielectric and calorimetric properties in the cure reaction of two thermosets by dielectric analysis and differential scanning calorimetry

Dielectric analysis and differential scanning calorimetry were used to study the cure reaction of an epoxy resin (the diglycidyl ether of bisphenol A (DGEBA) (n = 0)) and two curing agents, ie 1,2‐diamine cyclohexane (1,2‐DCH) and m‐xylylenediamine (m‐XDA). Various dielectric properties, such as the relaxed permittivity, unrelaxed permittivity and dipole strength, were determined as a function of the curing time, temperature and conversion. The dielectric curing properties observed were related to geometric and energetic aspects of the samples. Analysis of the results shows that the relaxed permittivity and dipole strength are higher for the system DGEBA (n = 0)/1,2‐DCH than for the system DGEBA (n = 0)/m‐XDA. Copyright © 2005 Society of Chemical Industry     

High temperature circular position sensor based on a giant magnetoresistance nanogranular Ag/sub x/Co/sub 1-x/ alloy

A new circular position sensor based on giant magnetoresistances has been developed. The sensing film is an AgCo nanogranular thin film patterned in a circular Wheatstone bridge configuration. This alloy shows a high magnetoresistance (8%) at room temperature within the field generated by an NdFeB permanent magnet that provides a sensitivity of 440 /spl mu/V/V/(/spl deg/). The operational temperature range of this sensor is -40/spl deg/C/+120/spl deg/C, although the magnetic film tolerates higher temperatures up to 200/spl deg/C. These parameters and the contactless way of sensing make this device appropriate for automotive applications. The developed sensor presents excellent characteristics for life, since it is not sensitive to pollution; it is frictionless and does not present any type of electrical noise generated by contacts.     

Low power VLSI architecture design of BMC,BPSC and PC schemes

Line coding is used to tune the wave form based on the properties of the physical channel. Bi-Phase Mark Coding (BMC), Bi-Phase Space Coding (BPSC) and Phase Coding (PC) are used as Line coding techniques. The first objective of the proposed work is to design Generation and Degeneration operations of BMC, BPSC and PC techniques in a single chip. The second objective is to reduce the area and power consumption, by modifying the number of MOS devices used to design the system and by adjusting the width of the MOS devices. The proposed system is designed with 59 transistors and simulated using Cadence^® 90 nm technology. This occupies 1290 µm². Required power can be reduced up to 33% by using any one of the suitable coding among BMC, BPSC and PC based on the properties of the input data signal. If the input data has equal possibility of high and low level signals, PC technique will be suitable for power reduction. If the high level beats the low level, BPSC technique will be suitable. If the low level beats the high level, BMC technique will be suitable.     

Reducing Oxidation of Foods Through Antioxidant Active Packaging Based on Ethyl Vinyl Alcohol and Natural Flavonoids

The development of antioxidant active packaging systems is attracting considerable attention as one of the preferred emerging technologies for reducing the incidence of lipid peroxidation. This work presents the use of ethylene vinyl alcohol copolymer films containing two natural flavonoids, catechin and quercetin, to reduce the oxidation of food. In a series of experiments, these materials showed their ability to reduce the presence of hydroxyl radicals in the package headspace. Packaging fried peanuts in bags manufactured with these active films resulted in a large reduction in the presence of hexanal, a compound produced during peroxidation of the unsaturated fat in peanuts. The results indicated that the materials actively reduced the presence of radical oxidative species although the antioxidants are not released into the food. On exposing sunflower oil to the films, the peroxide values obtained showed that the films actively protected the oil; because of the higher solubility of quercetin in this food product as well as the higher antioxidant capacity, the samples containing this flavonoid were more efficient. Industrial relevance: Active packaging is receiving considerable attention as an emerging technology that can be used to improve the quality and the stability of food, reducing the direct addition of chemicals and the need for changes in formulation. The results of this study show that it is possible to reduce food oxidation without adding antioxidants to the food. The films obtained can be used to protect any type of food, including dry or fatty products. Copyright © 2012 John Wiley & Sons, Ltd.     

SiO2/TiO2 thin films with variable refractive index prepared by ion beam induced and plasma enhanced chemical vapor deposition

SiO₂/TiO₂ optical thin films with variable compositions have been prepared by ion beam induced and plasma enhanced chemical vapour deposition (IBICVD and PECVD). While the films obtained by IBICVD were very compact, the PECVD ones with a high content of Ti presented a columnar microstructure. The formation of Si–O–Ti bonds and a change in the environment around titanium from four- to six-coordinated has been proved by vibrational and X-ray absorption spectroscopies. The refractive index increased with the titanium content from 1.45 to 2.46 or 2.09 for, respectively, the IBICVD and PECVD films. Meanwhile, the band gap decreased, first sharply and then more smoothly up to the value of pure TiO₂. It is concluded that the optical properties of SiO₂/TiO₂ thin films can be properly tailored by using these two procedures.     

Carbon monoxide detector fabricated on the basis of a tin oxide novel doping method

Toxic gas detection is a common issue of interest in domestic as well as industrial environments. There are, in fact, accurate methods to measure gas concentrations (Fourier transform infrared, gas chromatographs, or mass spectrometers) but they are too expensive and require skilled operators. Therefore, these complex detection systems are not useful for many applications, such as hazardous gas level detection in domestic appliances. In this paper, investigations lead to the fabrication of a micromachined tin oxide device for carbon monoxide detection in domestic environments. Relevant parameters that influence gas detection are analyzed and thus the device fabrication process defined by means of microtechnologies. Throughout the material optimization for CO detection, three different additive adding methods by dc sputtering PVD technique are studied and compared for two additives: Pt and Pd.     

Shape design sensitivity analysis in elasticity using the boundary element method

This paper deals with sensitivity analysis of the different functionals appearing in optimum shape design in elasticity using boundary element method (BEM). First, a general review concerning sensitivity analysis of the most usual functionals in elasticity is presented, based on the continuum approach. The accuracy in sensitivity analysis depends on the accuracy in evaluating strains and stresses on the boundary. A general procedure for strain calculation based upon some results of differential geometry of surfaces is shown. Another essential aspect in sensitivity analysis is the definition of the design velocity on the boundary, which defines the change in the geometry of the elastic solid. A computational treatment independent of the design variables used is presented, defining nodal values of the design velocity and taking advantage of the boundary element approximation. Finally, the feasibility and accuracy of the proposed procedures are assessed through several example problems.     

Tunable shapes in supported metal nanoparticles: From nanoflowers to nanocubes

The facile preparation of a range of supported nanoparticles on porous materials was successfully accomplished through the use of a range of environmentally friendly protocols including a modified impregnation/reduction methodology, ultrasounds and microwave irradiation. Materials were characterised by transmission electron microscopy (TEM) and XPS. Different morphologies including conventional nanospheres, nanoflower aggregates, nanorod-like structures and nanocubes were achieved under different conditions. The reported supported nanoparticles are envisaged to have interesting applications in various areas including catalysis, optics and sensors.     

Preservation of aseptic conditions in absorbent pads by using silver nanotechnology

Silver nanoparticles have been formed in fluff pulp and nanostructured Lyocell fibres by immersion in silver nitrate, and a subsequent transformation of the adsorbed silver ions into elementary silver nanoparticles by physical (thermal/UV) or chemical (sodium borohydride) methods. Microscopy revealed that nanoparticles generated by physical methods were regular in shape and efficiently dispersed, while the chemical reduction produced highly aggregated nanoparticles. Nanoparticle size has been found relevant to guarantee high antimicrobial activity, being the samples with big aggregated silver nanoparticles almost inefficient. Indeed a satisfactory correlation between silver ion release and the antimicrobial efficiency against Escherichia coli and Staphylococcus aureus could be confirmed, and furthermore, the highest concentrations tested were efficient to reduce the microbial load in poultry exudates. This work demonstrates that especially designed absorbent materials could be optimised to preserve aseptic conditions during manipulation, leading to feasible applications of a silver based nanotechnology in food technology.     

Identification of 2-dodecylcyclobutanone and linear-alkanes as irradiation markers in sliced dry-cured ham

The usefulness of 2-dodecylcyclobutanone (2-DCB) and alkane hydrocarbons as irradiation markers in sliced dry-cured ham was evaluated by solid phase microextraction (SPME)-gas chromatography-mass spectrometry (GC–MS). To that aim, sliced dry-cured ham was irradiated with different irradiation doses and subsequently examined together with non-irradiated dry-cured ham used as a control sample. The SPME conditions utilized were selected as a consequence of performing an optimization process. The results found in this work reflected that the presence of 2-DCB may be used as an irradiation indicator in sliced dry-cured ham since it does not occur in non-irradiated samples. This confirms data reported in the literature on irradiated foods, other than ham. Likewise, the concentrations of alkanes C₁₄–C₁₇ increased considerably in samples irradiated with low doses, although a decrease was observed when high irradiation doses were used. As a consequence, the concentration of these compounds can also be used as an irradiation indicator when doses lower than 1.0 kGy are applied. These results are discussed.