A macrokinetic approach to crystallization applied to a new thermoplastic polyimide (New TPI) as a model polymer

The application of a new macrokinetic approach to polymer crystallization is applied in this work to a new thermoplastic polyimide (New TPI) recently developed as a matrix of advanced polymer matrix composites. The slow crystallization kinetics presented by New TPI in the entire range between the glass-transition temperature and the melting point makes TPI an excellent model polymer for testing crystallization models. In the approach presented here the variation of the induction time with the temperature is included in the Nakamura model for nonisothermal crystallization, and a simplified expression of the kinetic constant as a function of the temperature is adopted. The proposed model is verified through a comparison with a complete set of experimental data, ranging from the melting point to the glass-transition temperature of the polymer, obtained in isothermal and nonisothermal conditions. Moreover phase transformation diagrams (TTT and CCT plots) are presented, providing a fundamental tool for understanding the crystallization behavior of semicrystalline matrices and to determine the more appropriate processing conditions. © 1995 John Wiley & Sons, Inc.     

Validation of the rancimat test for the assessment of the relative stability of fish oils

The induction periods for the peroxidation of various fish oils at 55–90°C were studied by the Rancimat test. The natural logarithms of the induction periods varied linearly with respect to temperature, with a mean coefficient of −7.5×10⁻²°C⁻¹, which was significantly different from that reported for vegetable oils. The activation energy for the formation of volatile acids had a mean value of 38.9 kJ/mol and was independent of the fish oil source. Peroxide formation under Rancimat test conditions followed first-order kinetics. The same kinetics were followed under Schaal Oven test conditions (forced-air oven, 60°C). On the basis of the results obtained, the Rancimat test appears to be useful in determining the relative stabilities of fish oils without the change in peroxide decomposition kinetics that may occur at elevated temperatures.     

Elastic modulus of nanostructured polymer surfaces

Living cell cultures exhibit improved adhesion on polymer surfaces engineered with nano-scale structures as compared to their flat counterparts. During fabrication their polymer-chain structure can be altered, thus affecting their mechanical properties. Here, we demonstrate using atomic-force-microscope nanoindentation that the modulus of nanostructured PDMS is doubled, while that of nanostructured ORMOCER increases by an order of magnitude, when compared to their flat counterparts.     

Electrical characterization of graphene synthesized by chemical vapor deposition using Ni substrate

In this work, the electrical characterization of graphene films grown by chemical vapor deposition (CVD) on a Ni thin film is carried out and a simple relation between the gate-dependent electrical transport and the thickness of the films is presented. Arrays of two-terminal devices with an average graphene film thickness of 6.9 nm were obtained using standard fabrication techniques. A simple two-band model is used to describe the graphene films, with a band overlap parameter E(0) = 17 meV determined by the dependence of conductivity on temperature. Statistical electrical measurement data are presented for 126 devices, with an extracted average background conductivity σ = 0.91 mS, average carrier mobility μ = 1300 cm(2) V(-1) s(-1) and residual resistivity ρ = 1.65 kΩ. The ratio of mobility to conductivity is calculated to be inversely proportional to the graphene film thickness and this calculation is statistically verified for the ensemble of 126 devices. This result is a new method of graphene film thickness determination and is useful for films which cannot have their thickness measured by AFM or optical interference, but which are electrically contacted and gated. This general approach provides a framework for comparing graphene devices made using different fabrication methods and graphene growth techniques, even without prior knowledge of their uniformity or thickness.     

Characterization of Jatropha curcas oils and their derived fatty acid ethyl esters obtained from two different plantations in Cuba

The scope of this work is to evaluate some properties of the oils and derived fatty acid ethyl esters (FAEE) from two different Jatropha Curcas species planted in Cuba. The properties that were determined include the acid value, peroxide value, p-anisidine value and fatty acid ethyl esters composition. In order to study the influence of the genus species and geographic conditions on the fuel properties, the oils from Jatropha Curcas planted in two regions of Cuba and their derived FAEE were analyzed and compared. The two plantations were in San José (SJ) and Guantanamo (Gt) representing respectively the western and eastern part of the island.The analyses indicated that the FAEE obtained from Guantanamo has a higher acid value and peroxide value compared with the FAEE from San José. The p-anisidine values did not show a clear trend and the results of gas chromatography-mass spectrometry indicated a similar FAEE composition. The results obtained by gas chromatography are in good agreements with previous reports.     

Release of folic acid in mesoporous NFM-1 silica

Mesoporous NFM-1 silica with folic acid as template was prepared taking advantage of the supramolecular self-assembly of pterin groups and their abilities to form hexagonal liquid crystal phases. NFM-1 materials with the varied morphologies such as fiber, chiral twisting long-rod, gyroid, and amorphous particles were prepared by varying the amount of the co-structure directing agent, stirring speed and changing pH value of the synthesis. The release kinetics of NFM-1 samples with different morphologies were studied in phosphate buffer with pH = 7.4 in 37 degrees C under stirring. All the release kinetic curves are fitted by the power law and Higuchi equations. The fitting of the power law equation was separately done as for the released amount up to 60% or 100%. The materials show slow, long-term and sustained release of folic acid from mesoporous NFM-1 silica, which establishes a new foundation for the potential application in drug delivery and bioimaging.     

Decay ratio estimation based on time–frequency representations

A novel method based on bilinear time–frequency representations (TFRs) is proposed to determine the time evolution of the linear stability parameters of a boiling water reactor (BWR) using neutronic noise signals. TFRs allow us to track the instantaneous frequencies contained in a signal to estimate an instantaneous decay ratio (IDR) that closely follows the signal envelope changes in time, making the IDR a measure of local stability. In order to account for long term changes in BWR stability, the ACDR measure is introduced as the accumulated product of the local IDRs. As it is shown in this paper, the ACDR measure clearly reflects major long term changes in BWR stability. Last to validate our method, synthetic and real neutronic signals were used. The methodology was tested on the Laguna Verde Unit 1, two events were reported in the Forsmark stability benchmark.     

Effect of native and acetylated‐crosslinked waxy corn starch‐beeswax coatings on quality attributes of raspberries during storage

Edible coatings (ECs) are a thin layer of a mixture of edible materials, applied in the liquid state and dried over the surface of a food product to maintain its quality during storage. This work was aimed to study the effect of ECs made from wx corn starch (WCS) or acetylated cross‐linked starch (ACLS) added with beeswax on fresh raspberry quality attributes during short‐term cold storage. Freshly harvested fruits were coated, dried, packed in plastic trays and stored up to 8 days at 4°C. During storage quality parameters such as firmness, respiration rate, anthocyanins content, total phenols, color changes, and weight loss were evaluated. A clear effect on control of respiration rate was observed in coated raspberries. Respiration rate of uncoated fruit was 4.5 ± 0.28 mmol/kg/h and decreased to 4.2 ± 0.27 for ACLS and to 4.1 ± 0.08 mmol/kg/h for WCS‐coated raspberries, after 56 h of storage at 15°C. Ethylene production followed a similar trend under these conditions decreasing from 0.043 ± 0.005 to 0.034 ± 0.004 mmol/kg/h for uncoated and ACLS coated fruits, respectively, indicating an effect on ripening control. Additionally, ACLS and WCS coatings permitted the preservation of color without affecting anthocyanins content. However, the presence of anaerobic metabolites and reduction of terpenes production in cold stored coated raspberries indicated hypoxic conditions, which can adversely affect shelf‐life quality attributes of raspberries such as firmness and weight loss.     

Coordinate-descent super-resolution and registration for parametric global motion models

We present a method for simultaneously obtaining registration and super-resolution from a sequence of low resolution images, based on a coordinate-descent approach. The novelty of the algorithm resides on the registration step, which can be applied easily to any parametric global motion model. We prove the validity of the model with synthetic and real data experiments, being of special interest the good performance achieved in the difficult case of images registered under a projective transformation.     

Effect of UV–Vis Photochemical Processing on Pear Juices from Six Different Varieties

The effect of ultraviolet irradiation on the activity of polyphenol oxidase and peroxidase in pear juices from six different varieties (Abate Fétel, Passa Crassana, Ercolini, Flor de Invierno, Blanquilla, and Conference) was investigated. The samples were irradiated for 120 min with a 400-W nominal power medium-pressure mercury lamp, emitting in a range between 250 and 740 nm. The temperature was kept at 25?±?1 °C with help of a refrigeration system consisting on a metallic coil fed with cold water. Polyphenol oxidase was inactivated in different rates, depending on each variety’s properties. Besides, as irradiation time increased, there was a general decrease in the absorbance spectrum, which means that some of the juice’s pigments could have been damaged. This decrease was especially significant between 400 and 450 nm. These changes were also observed by means of CIELab parameters. Vitamin C also decreased during the treatment. No variations in the pH, soluble solids, and sugar content were observed.