Why higher resolution graphics cards are needed in colour vision research

The colour resolution of a 14‐bit and an 8‐bit per channel graphics card were evaluated and compared with the just noticeable difference between colours (varying only in luminance) for: (1) a standard observer (based on the CIE 1976 L*u*v* colour space) and (2) real observers in a colour discrimination task. The results of this study show that an 8‐bit per channel graphics card seems adequate for colour discrimination experiments where stimuli only vary in luminance. However, considering that the resolution of the graphics card should be equal to the Nyquist rate, an 8‐bit per channel card turns out to be inadequate. For colour discrimination experiments where stimuli only vary in chromaticity, there is an undersampling of the colour space with respect to MacAdam ellipses when using 8‐bit per channel graphics cards. The extremely fine colour resolution of a 14‐bit per channel graphics card overcomes these problems. Its use allows more accurate measurements of achromatic and chromatic discrimination thresholds and avoids experimental (spatial or luminance) artefacts, such as bandings that can occur on achromatic or chromatic gradients. © 2010 Wiley Periodicals, Inc. Col Res Appl, 2011     

Phosphorus dynamics in permanent pastures: differential fertilizing and the animal effect

The general objective of this study was to evaluate the deviation between measured and estimated soil phosphorus (P) content, over 3 years, in a permanent bio-diverse pasture system in Southern Portugal with grazing sheep, and subjected to annual, differential P fertilization. The results can be a contribution to the development of practical and effective site-specific management strategies to minimize pasture yield variation. The soil and pasture samples were taken from a 6 ha field and were geo-referenced with RTK GPS. This procedure was carried out, each year, from March to May, according to the vegetative growth of the pasture. In October of each year the field was fertilized in a differential manner, as a function of soil P concentration measured at the end of the pasture growth cycle (May–June). Maps were developed in ARCGIS 9.3 considering: (1) the soil P concentration and pH; (2) the average P plant uptake; (3) the differential P application; and (4) the extractable P. The significant temporal variability of soil P concentration and pasture dry matter yield confirm the complexity of soil P dynamics in pastures involving two biological systems: plant and animal, under Mediterranean conditions and the consequent difficulties in implementing precision agriculture techniques. The results of this work indicate that 3 years of P variable-rate application rate were not sufficient to obtain homogeneous and adequate levels of P in the whole field for crop production. Despite differential P fertilization with the objective of obtaining homogenous values of soil P content in experimental field, the undulating topography of the experimental field associated with the presence of grazing animals adds a notable short-range spatial variation in nutrients that generally arises from heterogeneous excreta depositions. The small and positive final deviation between measured and estimated P levels suggests the irregular and gradual release of P by the fertilizer over years, contributing to an increase in soil P concentration. P input in fertilizer and removal in the crop greatly exceed all other inputs and outputs. However, the pH effect on extractable P, the estimation of amounts of export/import by livestock, atmospheric deposition or erosion/leaching losses are complex and justify more experiments to evaluate the confidence of long-term estimated P dynamic balance before sustained decision making is possible for differential pasture fertilization and site-specific management strategy implementation.     

Dynamic viscosity of olive oil as a function of composition and temperature: A first approach

Knowledge of the viscosity of virgin olive oils (VOOs) is of great importance for the design of pilot plants, to determine the time required for the settling of particles at the end of the production chain and from a sensory view point. The dynamic viscosities of French VOOs from four different cultivars (‘Aglandau’, ‘Bouteillan’, ‘Salonenque’ and ‘Tanche’) were studied as a function of their fatty acid and TAG compositions and of the temperature [10–50°C]. These four VOOs had different TAG and fatty acid compositions representative of the range of compositional variations in the main French oils. Their viscosities were similar, although small but measurable differences that depended on their compositions were apparent. All the VOO samples exhibited the same dynamic viscosity pattern over temperature. For a given temperature, the viscosity difference was the greatest between Aglandau and Salonenque oils, Aglandau being the oil with the highest viscosity. The correlation between temperature and viscosity was highlighted by an Arrhenius model for this Newtonian fluid. The Arrhenius activation energy was correlated (R² = 0.993) with the percentage of triolein, the main TAG in olive oil.     

Effects of annealing on the hierarchical crystalline structures and mechanical properties of injection‐molded bars of high‐density polyethylene

The effect of annealing on the microstructural evolution and mechanical properties of high‐density polyethylene parts molded via gas‐assisted injection molding was investigated using scanning electron microscopy, differential scanning calorimetry, two‐dimensional wide‐angle X‐ray diffraction and tensile testing. The results indicated that a variety of annealing temperatures could induce considerable variations in the hierarchical structures, crystallinity, lamellar thickness and yield stress of the molded bars. According to these results, the annealing temperatures could be divided into three regions. In the low‐temperature region of annealing at 80 °C, the spatial variation of the superstructure developed along the thickness direction and mechanical properties of the annealed sample were mainly unchanged and similar to those of the original specimen. At 100 and 120 °C, the intermediate temperature region of annealing, the thickness of the crystals, degree of orientation and yield stress of annealed samples were greatly improved. Finally, at 127 °C, the degree of orientation decreased and yield stress slightly improved, an indication of the high‐temperature annealing region being characterized by increasing melting/recrystallization and causing relaxation of oriented molecular chains. A model is proposed to interpret the mechanism of the annealing treatment of the samples at various temperatures. © 2013 Society of Chemical Industry     

The effect of montmorillonite and compatibilizer quantities on stiffness and toughness of polyamide nanoblends

Although polymer blend nanocomposites are widely studied, the balance between stiffness and toughness has not yet been investigated in detail. Some materials producers as well as some sectors in the automotive industry try to improve the toughness of materials without an important loss in stiffness. With this in mind, the aim of the study reported here was to obtain a good balance between toughness and stiffness of polymer blends with different amounts of clay and compatibilizer. In this context, the microstructure of polyamide 6/ethylene–propylene–diene metallocene terpolymer/(ethylene–propylene–diene copolymer)‐graft‐(maleic anhydride) blends with various amounts of clay (2, 3, 4 and 5 wt%) and compatibilizer (10 and 20 wt%) was studied to analyse the achieved morphology to understand the macroscopic properties. The morphology of the rubber phase and the dispersion of the montmorillonite (MMT) are the main factors that influence the mechanical properties. In this sense, the highest Young's modulus is achieved for nanoblends with 5 wt% of MMT, although this nanoblend has the lowest value of notched Izod impact strength. The results obtained suggest that there is a clear trade‐off between stiffness, toughness and temperature behaviour when the ratio of (ethylene–propylene–diene copolymer)‐graft‐(maleic anhydride) to MMT is 5:1. Copyright © 2009 Society of Chemical Industry