Shaping gels and gels mixture to create helices

In cooking, food gels, such as agar-agar or alginate, are often prepared and presented in the form of spheres or spaghetti. While experimenting in our kitchen, we realized that it is quite difficult to make more advanced shapes. In this study, we sought to develop new methods to obtain more complex shapes. Our first challenge was to obtain helices. The best method we selected was to deposit the solutions before their gelation in a thread. The robustness of the method is tested by systematically changing the thread pitch, diameter, and depth. From the deformation under its own weight, we propose to deduce the mechanical characteristics of the helix. These values are compared to those obtained in the laboratory using indentation testing. Finally, we experimented with mixed gels obtained by combining agar-agar and alginate.Fil: D'angelo, María Verónica. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Buenos Aires. Facultad de Ingeniería. Departamento de Física. Grupo de Medios Porosos; ArgentinaFil: Pauchard, L.. Centre National de la Recherche Scientifique; FranciaFil: Auradou, H.. Centre National de la Recherche Scientifique; FranciaFil: Darbois Texier, B.. Centre National de la Recherche Scientifique; Franci

Friction of a sphere rolling down a granular slope

The present study investigates the rolling motion of a rigid sphere moving down a granular slope. We observe that the sphere only moves steadily beyond a critical inclination that depends on the diameter and density of the sphere. The groove created on the bed surface during the passage of the sphere, grows with the diameter and density of the sphere and it is nearly independent of both the sphere speed and the slope angle. The granular resistance experienced by the rolling sphere is deduced from its dynamics. A mechanical description of the interaction between the sphere and the granular bed accounts for the experimental findings through a single adjustable parameter. A phase diagram for the sphere dynamics defined by two dimensionless parameters, namely the slope angle and the ratio of the densities of the sphere and of the grains, is proposed

Weightlifting and the actomyosin cycle

International audienc

Friction of a sphere rolling down a granular slope

International audienceThe present study investigates the rolling motion of a rigid sphere moving down a granular slope. We observe that the sphere only moves steadily beyond a critical inclination that depends on the diameter and density of the sphere. The groove created on the bed surface during the passage of the sphere, grows with the diameter and density of the sphere and it is nearly independent of both the sphere speed and the slope angle. The granular resistance experienced by the rolling sphere is deduced from its dynamics. A mechanical description of the interaction between the sphere and the granular bed accounts for the experimental findings through a single adjustable parameter. A phase diagram for the sphere dynamics defined by two dimensionless parameters, namely the slope angle and the ratio of the densities of the sphere and of the grains, is proposed