Ashkan Vaziri's blog

Two postdoctoral fellow positions at Northeastern University are available immediately, focused on the analysis of the nonlinear behavior of structures and soft matter using computational mechanics and the development and analysis of active cellular structures, and biomimetic materials. The research will be carried out at the High Performance Materials and Structures Laboratory (http://www.hpmsl.neu.edu/).

Two postdoctoral fellow positions at Northeastern University is available immediately, focused on the analysis of the nonlinear behavior of structures and soft matter using computational mechanics and the development and analysis of active cellular structures, and biomimetic materials. The research will be carried out at the High Performance Materials and Structures Laboratory (http://www.hpmsl.neu.edu/).

Two postdoctoral fellow positions at Northeastern University are available immediately. First position is focused on the analysis of the nonlinear behavior of soft matter using computational mechanics and the development and analysis of biomimetic materials and structural systems. Second position is focused on computational and solid mechanics. The research will be carried out at the High Performance Materials and Structures Laboratory (http://www.hpmsl.neu.edu/).

Recent developments in computational cell and biomolecular mechanics have provided valuable insights into the mechanical properties of cells, subcellular components and biomolecules, while simultaneously complementing new experimental techniques used for deciphering the structure–function paradigm in living cells. These computational approaches have direct implications in understanding the state of human health and the progress of disease and can therefore aid immensely in the diagnosis and treatment of diseases.

In nature, several species use flexible probes to actively explore their environment, and acquire important sensory information, such as surface topology and texture, water/air flow velocity, etc. For example, rats and other rodents have an array of facial vibrissae (or whiskers) with which they gather tactile information about the external world.  The complex mechanisms, by which mechanical deformations of the probe lead to neuronal activity in the animal’s nervous system are still far from being understood. This is due to the intricacy of the deformation mechanics of the flexible sensors, the processes responsible for transforming the deformation to electrical activity, and the subsequent representation of the sensory information by the nervous system. Understanding how these mechanosensory signals are transduced and extracted by the nervous system promises great insight into biological function, and has novel technological applications. To understand the mechanical aspect of sensory transduction, here we monitored the deformation of a rat’s vibrissa as it strikes rigid objects with different topologies (surface features) during locomotion, using high-speed videography. Motivated by our observations, we developed detailed numerical models to study the mechanics of such flexible probes. Our findings elucidate how active sensation with vibrissae might provide sensory information and in addition have direct implications in several technological areas. To put this in perspective, we propose strategies in which flexible probes can be used to characterize surface topology at high speeds, which is a desirable feature in several technological applications such as memory storage and retrieval. (The full article is attached)

The increasing use of fiber-reinforced composites accentuates the need for developing multi-axial fatigue failure models for these materials. In this article (attached), we proposed several multiaxial fatigue failure models for fiber-reinforced composites considering the contribution of mean and cyclic normal stress/strain and shear stress/strain at the plane of failure and examined their capability for predicting the fatigue life of the E-glass/epoxy composite materials.

The response of low-dimensional solid objects combines geometry and physics in unusual ways, exemplified in structures of great utility such as a thin-walled tube that is ubiquitous in nature and technology.

A stiff skin forms on surface areas of a flat polydimethylsiloxane (PDMS) upon exposure to focused ion beam (FIB) leading to ordered surface wrinkles. By controlling the FIB fluence and area of exposure of the PDMS, one can create a variety of patterns in the wavelengths in the micrometer to submicrometer range, from simple one-dimensional wrinkles to peculiar and complex hierarchical nested wrinkles. Examination of the chemical composition of the exposed PDMS reveals that the stiff skin resembles amorphous silica. Moreover, upon formation, the stiff skin tends to expand in the direction perpendicular to the direction of ion beam irradiation. The consequent mismatch strain between the stiff skin and the PDMS substrate buckles the skin, forming the wrinkle patterns. The induced strains in the stiff skin are estimated by measuring the surface length in the buckled state. Estimates of the thickness and stiffness of the stiffened surface layer are estimated by using the theory for buckled films on compliant substrates. The method provides an effective and inexpensive technique to create wrinkled hard skin patterns on surfaces of polymers for various applications. Click here for access to the full article. See also the press release: Applied scientists create wrinkled 'skin' on polymers