Tribological Properties of 1-Alkenes on Copper Foils: Effect of Low-Coordination Surface Sites

It has been suggested from molecular dynamics simulations that low-coordination-number sites are produced at a sliding metal–metal interface, but, because of their instability, they may rapidly relax to increase their coordination number. The possible presence of such low-coordination sites on the surface is tested by exploiting the observation that the desorption temperatures of 1-alkenes on copper increase with both the number of carbons atoms in the 1-alkenes and the surface roughness. Thus, 1-alkenes desorb from a Cu(111) single crystal, with relatively few low-coordination sites, at temperatures between 60 and 100 K lower than from a polycrystalline copper foil. The decrease in friction after impinging a flux of various 1-alkenes on a copper foil, while rubbing in an ultrahigh vacuum tribometer, correlates very well with the corresponding 1-alkene coverages on a copper foil, estimated using the desorption kinetics. This suggests either that rubbing does not result in the formation of lower-coordination sites or that they relax sufficiently rapidly that they do not influence the surface chemistry of 1-alkenes. Surface analyses indicate that shear at the interface causes carbon to diffuse into the subsurface region to form a tribofilm.     

Structural characterization of LDPE/EVA blends containing nanoclay‐flame retardant combinations

The combination of different types of organo‐modified montmorillonite (MMT) with aluminum hydroxide (aluminum trihydrate—ATH), as a flame retardant system for polyethylene‐ethylene vinyl acetate (LDPE/EVA), blends were studied. Five different types of organically modified montmorillonite clays, each with different modifier, were used. The structural characterization was carried out by X‐ray diffraction (XRD) and scanning electron microscopy in transmission mode (STEM). The mechanical and rheological properties were also evaluated. The XRD analysis showed a clear displacement of the d₀₀₁ signal, which indicates a good degree of intercalation, especially for the MMT‐I28 and MMT‐20, from Nanocor and Southern Clay Products, respectively. The presence of ATH and the compatibilizer did not have any effect on the exfoliation of the studied samples. The thermal stability and flame retardant properties were evaluated by thermogravimetric analysis (TGA), limiting oxygen index (LOI—ASTM D2863), and flammability tests (Underwriters Laboratory—UL‐94). The effect of different compatibilizers on the clay dispersion and exfoliation was studied. The results indicated that the addition of montmorillonite makes it possible to substitute part of the ATH filler content while maintaining the flame retardant requirements. The thermal stability of MMT/ATH‐filled LDPE/EVA blends presented a slight increase over the reference ATH‐filled LDPE/EVA blend. Compositions with higher clay content (10 wt %) showed better physicochemical properties. The increased stability of the higher clay content compositions results from the greater inorganic residual formation; this material has been reported to impart better performance in flammability tests. The mechanical properties and flame retardancy remained similar to those of the reference compound. The reduced ATH content resulted in lower viscosities and densities, facilitating the processing of the polymer/ATH/clay compounds. Extrusion of these compounds produced a lower pressure in the extrusion head and required reduced electrical power consumption. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Fruit quality: new insights for biotechnology

At ripening fruits undergo many changes which include the development of color and aroma and improvements in flavor and texture that make them attractive to potential consumers. Fruits provide an important source of health-related substances, plus minerals and vitamins, and the quality of a fruit is influenced by variety, nutritional status, and environmental conditions during plant growth and fruit development. Ripening is considered to be the main process in fruit development, and all studies had been focused on this process which included physicochemical, biochemical, and molecular analysis. With the development of genomic analysis the strategies to study fruit ripening have been changing and now there are new perspectives and opportunities. The objective of this review is to describe the state of the art in the studies related to fruit ripening with emphasis in molecular studies.     

Relating Molecular Structure to Tribological Chemistry: Borate Esters on Copper

The surface and tribological chemistry of 2-propanol and borate esters, isopropoxy tetramethyl dioxaborolane (ITDB), and tetramethyl dioxaborolane (TDB) as gas-phase lubricants for copper surfaces are compared by measuring the friction coefficient and contact resistance in an ultrahigh vacuum tribometer. 2-propanol reacts on copper below room temperature to desorb primarily acetone and causes no friction reduction when used as a gas-phase lubricant. TDB decomposes to deposit BO_x species on the surface and produces an initial decrease in friction coefficient that is not sustained. ITDB, which reacts at room temperature to form a tetramethyl dioxaborolide species on the surface, results in an immediate and sustained decrease in friction coefficient when used as a gas-phase lubricant for copper. This indicates that the surface chemistry of the borate esters can be correlated with their tribological properties and illustrates the effect of replacing a hydrogen atom in TDB with a 2-propoxy group in ITDB on both the surface and tribological chemistry. Analysis of the species formed in the wear track after lubrication with ITDB reveals the presence of graphitic or diamond-like carbon and oxygen, and these elements are also found in the subsurface region of the sample. Rubbing the sample in vacuo after reacting with ITDB shows the removal of a boundary film where the coefficient remains constant and the subsequent removal of the subsurface layer in which the contact resistance rises to its original value.     

Effect of maize genotype,developmental stage,and cooking process on the nutraceutical potential of huitlacoche (Ustilago maydis)

Huitlacoche galls were produced in 15 creole maize genotypes harvested at two stages of development, 23 and 28 days after inoculation, and in a hybrid genotype harvested at six stages of development. Raw and cooked galls were evaluated for proximate constituents, carbohydrate composition and antimutagenic activity. Huitlacoche grown in creole maize exhibited differences in concentrations of some of the proximate and carbohydrate components, due to genotype and stage of development; some effects were also observed in hybrid maize, as a result of stage of development and cooking. Huitlacoche has a considerable amount of crude protein (9.8% average in creole maizes, and 11.3% in hybrid maize). Most of the values for total dietary fibre, β-glucans, and total free sugars were higher than those reported for other edible mushrooms. The high concentration of antimutagenic substances appears to be an asset of this culinary delicacy.     

Functional properties of safflower protein isolates: Water absorption,whipping and emulsifying characteristics

Safflower meal defatted at the laboratory (SML) and safflower cake provided by an industrial plant (SMI) were used for protein isolation. Isolates were obtained by micellisation (MP) and isoelectric precipitation (IP) techniques. The functional properties studied with these isolates were water and fat absorption, foam expansion and stability, and emulsion activity and stability. Within the experimental conditions of this research, it was observed that the various treatments received previously by the safflower meal, for oil extraction, seemed to have comparatively minor effects on the functional performance of the protein isolates. Only in the case of SML, did the MP isolates have a higher water and fat absorption, and foam expansion than IP samples. For both SML and SMI, the emulsion stability of MP was higher than that of IP.     

Photoreflectance of r.f. sputtered Cd1−xFexTe thin films

Samples of r.f. sputtered Cd_1–x Fe _x Te (withx = 0.00, 0.05, 0.10 and 0.15) films were studied by photoreflectance spectroscopy. The samples were grown at a substrate temperature of 150°C. The photoreflectance spectra around the fundamental edge were analysed using the generalized theory of electroreflectance in the low-field regime recently developed by Raccahet al. The experimental results forx = 0.00 and 0.05 show a single feature that can be intepreted in terms of optical transitions in a cubic phase structure. In those films wherex =0.10 and 0.15, the experimental results show a double feature spectrum that we attribute to optical transitions in an hexagonal phase structure. Subsequent annealing at 200 and 300° C of the samples produces some changes in the lineshape of the photoreflectance spectra. These changes are interpreted in terms of an increment in the density of polarizable defects as the annealing temperature increases; we associate this effect with an increase in the formation of complex defects composed of Fe³⁺ ions and cadmium vacancies.On leave from the Instituto de Ciencias de la Universidad Autónoma de Puebla.     

BTX abatement using Chilean natural zeolite: the role of Br?nsted acid sites

In wastewater treatment facilities, air quality is not only affected by conventional unpleasant odour compounds; toxic volatile organic compounds (VOCs) are also found. In this study, the adsorptive capacity of Chilean natural zeolite toward VOC removal was evaluated. Moreover, the influence of zeolite chemical surface properties on VOC elimination was also investigated. Three modified zeolite samples were prepared from a natural Chilean zeolite (53% clinoptilolite, 40% mordenite and 7% quartz). Natural and modified zeolite samples were characterised by nitrogen adsorption at 77 K, elemental analyses and X-ray fluorescence (XRF). Chemical modifications of natural zeolite showed the important role of Br?nsted acid sites on the abatement of VOCs. The presence of humidity has a negative effect on zeolite adsorption capacity. Natural zeolites could be an interesting option for benzene, toluene and xylene vapour emission abatement.     

Attitude Stabilization with Real-time Experiments of a Tail-sitter Aircraft in Horizontal Flight

This paper focusses on the attitude stabilization of a mini tail-sitter aircraft, considering aerodynamic effects. The main characteristic of this vehicle is that it operates in either the hover mode for launch and recovery, or the horizontal mode during cruise. The dynamic model is obtained using the Euler–Lagrange formulation, and aerodynamic effects are obtained by studying the propeller effects. A nonlinear saturated Proportional-Integral-Derivative (SPID) control with compensation of aerodynamic moments is proposed in order to achieve the asymptotic stabilization of the vehicle in horizontal mode. In addition, a homemade inertial measurement unit (HIMU) is built for operating the complete operational range of the vehicle (including vertical and horizontal modes). Finally, simulation results are presented for validating the control law, and practical results are obtained in real-time during the flight.