Effect of conducting fillers on the microstructure and electrical conductivity of thermoplastic polymer composites

Summary This paper reports on the synthesis and characterization (electrical, mechanical, thermal and dynamic mechanical) of electrically conducting polymer composites based on thermoplastic matrices (low density polyethylene (LDPE) and polypropylene (PP)) and two conducting fillers: iron particles (Fe) and carbon black (CB). The addition of Fe allows the easy incorporation of higher amounts of CB. Results suggest that the electrical and mechanical properties of these materials are improved by the presence of both fillers being necessary the addition of CB to achieve interesting values of conductivity. On the other hand, the crystalline structure of the polymer matrix is gradually reduced with the incorporation of both fillers but Fe by itself does not affect the geometry of growing crystals.     

Solidification of NaCl–LiF–$$\hbox {CaF}_{2}$$ ternary composites

The purpose of this work is to refine the microstructure of eutectic halides, candidates to polaritonic metamaterials, through the directional solidification of ternary compositions. NaCl–LiF–\(\hbox {CaF}_{2}\) ternary composites have been solidified using Bridgman and micro-pulling-down techniques at pulling rates from 3 to 300 mm/h for the first time. The interparticle spacing is 12% smaller for this composition than for the binary fibrous NaCl–LiF eutectic. Conditions for solidification and growth in order to generate ternary aligned microstructures are discussed. The very small amount of melt remaining in the mixtures until \(580\,^{\circ }\hbox {C}\) is probably the consequence of solid solubility of LiCl in NaCl and the formation of the reciprocal salt pairs, as in NaCl–LiF. However, it does not prevent the solidification of homogenous ternary microstructures.     

Generation of smooth grids with line control for scattering from multiple obstacles

A new approach to generate structured grids for two-dimensional multiply connected regions with several holes is proposed. The bounding curves may include corners or cusps. The new algorithm constitutes an extension of the Branch Cut Grid Line Control (BCGC) technique introduced byVillamizar et al. [V. Villamizar, O. Rojas, J. Mabey, Generation of curvilinear coordinates on multiply connected regions with boundary-singularities, J. Comput. Phys. 223 (2007) 571–588] to domains with a finite number of holes. Regions with multiple holes are reduced to several contiguous single hole subregions. Then, the BCGC algorithm is applied to each single hole subregion producing a smooth grid with line control. Finally, the subregions with their respective grids are joined and their interfaces are smoothed resulting a globally smooth grid. The advantages of the novel grids are revealed by employing them to numerically solve acoustic scattering problems in the presence of multiple complexly shaped obstacles.     

Anisotropic error estimates for an interpolant defined via moments

Summary An interpolant defined via moments is investigated for triangles, quadrilaterals, tetrahedra, and hexahedra and arbitrarily high polynomial degree. The elements are allowed to have diameters with different asymptotic behavior in different space directions. Anisotropic interpolation error estimates are proved.      

A flight by periscope and where it landed

OBJECTIVE: This study defines display design factors linking visual accommodation and the perceived size of distant objects. BACKGROUND: In 1947, in anticipation of augmented contact and sensor-relayed contact displays, a periscope was installed in an airplane to serve as a sensor-based contact display simulator. To achieve normal landing performance, however, the unity image had to be magnified. This successful intervention, first published in 1966 in Human Factors, implicated oculomotor mechanisms and higher perceptual functions and became the observational basis for a series of investigative hypotheses. METHOD: Observers registered the perceived size of the collimated image of a "moon" by adjusting a disk of light while alternatively providing optometric measurements of accommodative distance. RESULTS: Various investigators found high correlations between focal distances and perceived moon sizes. CONCLUSION: The simulated moon provided a superior vehicle for revealing the relationship between focal distance and perceived size and the factors affecting both. The operational display design implications and the possibility of a partial explanation for the moon illusion provided the motivation for an important doctoral research project involving eight factors that affect both focal distance and perceived size. APPLICATION: The investigation reaffirmed that virtual images, as found in head-up and head-mounted displays (HUDs and HMDs, respectively), do not consistently draw focus to optical infinity and that a variety of factors necessarily manipulated by display designers and present in many operational systems can affect visual performance partially through the mediation of accommodation.     

Design of a wavelength multiplexer-demultiplexer by the use of planar microlenses

The ray-tracing method is applied to design a wavelength multiplexer-demultiplexer by the use of planar microlenses as focusing and collimating elements. By simulating both uniform and Gaussian intensity distributions of the input sources, we find the position of the input-output components of the wavelength multiplexe-rdemultiplexer, which maximizes the coupling efficiency in each channel. Losses are also evaluated.     

A nonlinear hybrid controller for swinging-up and stabilizing the Furuta pendulum

The conventional switching strategy for solving the inverted pendulum control problem is based on two steps: swinging-up and stabilization. In this note, first, a new strategy for swinging the Furuta pendulum up towards the desired upright position is designed using the Speed-Gradient method, which uses only directly measured coordinates. Then, a nonlinear controller, based on the Forwarding approach, stabilizes the upright position. As a new contribution the latter leads to a nonlinear stabilizer around the upright position, whose Lyapunov function yields a larger size estimation of the domain of attraction than the one obtained with the traditional linear approach. This estimation allows us to use it in a global switching strategy in the practical implementation and guarantees almost-global asymptotic stability of the equilibrium. Successful experimental results are reported with the available laboratory Furuta pendulum.     

Application of a mathematical model to the study of the glass transition temperature in polymer electrolyte precursor systems

To the purpose of studying the effect of composition on the glass transition temperature (Tg) of a series of polymer electrolytes based on blends of polyethylene oxide (PEO), poly(octafluoropentoxytrifluoroethoxy)phosphazene (PPz) and poly(epichlorhydrine), a mathematical model was applied to results obtained through DSC determination using seven ternary blends selected by an experimental design. The parameters of the model were chosen by means of stepwise linear regression method. The final model proved to be appropriate (R² = 0.997; s = 0.99 K) to predict the Tg values. From a structural point of view it was found that the lowest Tg values were obtained for the blends containing the smallest PECH portion. Received: 18 November 1996/Revised: 2 December 1996/Accepted: 3 December 1996     

Iron and vitamin A deficiencies and prevalence of anemia in boys and girls between 6 to 24 months of age in Chaco,Argentina

To determine the prevalence of anemia, and iron (ID) and vitamin A deficiencies aiming at their prevention, 414 children between 6 and 24 months of age, were randomly selected from the whole province of Chaco. A sociodemographic survey was implemented, and hemoglobin (Hb), plasma ferritin and retinol were measured. Anemia prevalence (Hb < 110 g/L) was 66.4%, without differences between age groups, and included 18% with Hb < 90 g/L. These cases were significantly less in children 6-8 month of age (5.1%) than in the others (approximately equal to 20%) (P: 0.007). Mean Hb was also higher in 6-8 months old children and was associated with lower prevalence of ID (ferritin < 12 micrograms/L) (p < 0.000) but not with age (p = 0.8865). ID already present, however, in 36.6% of children in this age group, reached a prevalence of 72.9% in children older than 18 months. Anemia prevalence was significantly higher in males, in children whose birth weight was < 3000 g, in those who had never taken iron supplements and among the poor, both structural and by income. Retinol values < 20 micrograms/dl occurred only in 5.1% of children. Iron nutrition prior to, during pregnancy and in children during the first 2 years of life must be improved by joining strategies based on community empowerment aimed at improving dietary iron, assuring effective preventive supplementation and promoting the opportune umbilical cord ligation.     

Microemulsion phase behavior of anionic-cationic surfactant mixtures: Effect of tail branching

This research evaluated middle-phase microemulsion formation by varying the mole ratio of anionic and cationic surfactants in mixtures with four different oils (trichloroethylene, n-hexane, limonene, and n-hexadecane). Mixtures of a double-tailed anionic surfactant (sodium dihexyl sulfosuccinate, SDHS) and an unbalanced-tail (i.e., doubletailed with tails of different length) cationic surfactant (benzethonium chloride, BCl) were able to form microemulsions without alcohol addition. The amount of NaCl required to form the middle-phase microemulsion decreased dramatically as an equimolar anionic-cationic surfactant mixture was approached. Although the mixture of anionic and cationic surfactants demonstrated a higher critical microemulsion concentration (cμc) compared to the anionic surfactant alone, the Winsor Type IV single-phase microemulsion started at lower surfactant concentrations for the anionic-cationic mixture than for the anionic surfactant alone. Under optimum middlephase microemulsion conditions, mixed anionic-cationic surfactant systems solubilized more oil than the anionic surfactant alone. Pretreatment detergency studies were conducted to test the capacity of these mixed surfactant systems to remove oil form fabrics. It was found that anionic-rich mixed surfactant formulations yielded the largest oil removal, followed by cationic-rich systems.