Infants' predictive reaching for moving objects in the dark.

Infants were presented with a moving object under 2 lighting conditions to investigate the role of vision in early reaching. The motion of the target object also allowed for an analysis of the infants' ability to use a predictive style of reaching. Infants were tested twice, at 5 and 7.5 months of age, with a moving object in the light and the same object painted with luminescent paint in the dark. Infants successfully contacted the glowing object on about half of their attempts at both ages, although 7.5 month-olds reached more often. Infants also took into account the motion of the target object by aiming their reaches ahead of the object and by reaching with their contralateral hand. These results suggest that proprioceptive feedback and sight of the target allow for successful reaching with limited visual information, even in relatively complex reaching tasks. The infants' success also demonstrates their ability to adapt their movements and reaching strategy to the speed and trajectory of the target object in order to reach predictively. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Anticipating Cutoff Diameters in Deterministic Lateral Displacement (DLD) Microfluidic Devices for an Optimized Particle Separation

Deterministic lateral displacement (DLD) devices enable to separate nanometer to micrometer‐sized particles around a cutoff diameter, during their transport through a microfluidic channel with slanted rows of pillars. In order to design appropriate DLD geometries for specific separation sizes, robust models are required to anticipate the value of the cutoff diameter. So far, the proposed models result in a single cutoff diameter for a given DLD geometry. This paper shows that the cutoff diameter actually varies along the DLD channel, especially in narrow pillar arrays. Experimental and numerical results reveal that the variation of the cutoff diameter is induced by boundary effects at the channel side walls, called the wall effect. The wall effect generates unexpected particle trajectories that may compromise the separation efficiency. In order to anticipate the wall effect when designing DLD devices, a predictive model is proposed in this work and has been validated experimentally. In addition to the usual geometrical parameters, a new parameter, the number of pillars in the channel cross dimension, is considered in this model to investigate its influence on the particle trajectories.     

63Cu NMR in the normal state of HgBa2Ca2Cu3O8+δ

We present a⁶³Cu NMR study of HgBa₂Ca₂Cu₃O₈₊ underdoped single crystals with T_c 115 K. While the uniform spin susceptibility decreases below T_o 370 K, relaxation rate measurements demonstrate the opening of a spingap at Q = (, ) below T* 230 K, the highest temperature reported so far. The characteristic energy of spin fluctuations is shown to be higher than in underdoped YBa₂Cu₃O_7–, and the analysis of the quadrupole and hyperfine couplings suggests that the in-plane Cu-O hybridization is also stronger. The T-dependence of T₁ is the same in the three CuO₂ planes which seems hardly compatible with the pure interlayer spin-pairing picture.     

Mechanical and tribological properties of poly(hydroxyethyl methacrylate) hydrogels as articular cartilage substitutes

Poly(hydroxyethyl methacrylate) (p(HEMA)) hydrogels have been proposed as promising biomaterials to replace damaged articular cartilage. A major obstacle to their use as replacement bearing tissue is their poor mechanical properties in comparison with healthy articular cartilage. The purpose of this study was to obtain p(HEMA) hydrogels with physicochemical and mechanical properties close to healthy articular cartilage, by introducing a hydrophilic monomer, namely acrylic acid (AA). Formulations of hydrogels with different amounts of hydrophilic monomer (acrylic acid, AA) were synthesized and tested: p(HEMA), p(HEMA-co-5%AA), p(HEMA-co-25%AA). The macro-mechanical tests were reproduced at nanoscale in order to verify if the superficial properties of the hydrogels are similar to the bulk ones.     

Capillary self-alignment of polygonal chips: a generalization for the shift-restoring force

Capillary-driven self-alignment using droplets is currently extensively investigated for self-assembly and microassembly technology. In this technique, surface tension forces associated to capillary pinning create restoring forces and torques that tend to bring the moving part into the alignment. So far, most studies have addressed the problem of square chip alignment on a dedicated patch of a wafer, aiming to achieve 3D microelectronics. In this study, we investigate the shift-restoring forces for more complex moving parts such as regular—convex and non-convex—polygons and regular polygons with regular polygonal cavities. A closed-form approximate expression is derived for each of these polygonal geometries; this expression agrees with the numerical results obtained with the Surface Evolver software. For small shifts, it is found that the restoring force does not depend on the shift direction or on the polygonal shape. In order to tackle the problem of microsystem packaging, an extension of the theory is done for polygonal shapes pierced with connection vias (channels), and a closed form of the shift-restoring force is derived for these geometries and again checked against the numerical model. In this case, the restoring force depends on the shift direction. Finally, a non-dimensional number, the shift number, is proposed that indicates the isotropic or anisotropic behavior of the chip according to the shift direction.     

Tribological behaviour of Pearlitic and Bainitic steel grades under various sliding conditions

Railway systems have to cope with increasing and heavier traffic conditions. New rail steel grades are designed to extend rail life and to prevent rail defects. The tribological response of such steel grades under wheel-rail contact conditions needs to be studied before its use on real track. Tests on reduced-scale simulator, i.e. roller-on-plate tribometer with wheel-rail contact like conditions, have been performed on three rail steel grades: the Pearlitic, the heat-treated Pearlitic and the Bainitic. Results show a difference in both sensitivity and mechanism of particle detachment with the steel grade microstructure, but no difference in friction coefficient evolution.