My research interests

The following list is not only incomplete, but is also in constant evolution, which in my opinion is the hallmark of a true theoretical physicist. To keep studying variations of the same problems means narrowing down and eventually leads to fossilization due to understimulation of the grey cells, something I fight with all my heart; sometimes an uphill battle. While this attitude had evident implications on my career (no one regards me as a specialist on any specific problem) it has the advantage of giving me a relatively broad horizon and has attracted quite a few collaborations, which keeps at bay a complete disillusion with the current practice of theoretical science.
On some of the projects below I have collaborators and on others I don't. Consequently, many of these issues are not progressing at a satisfactory pace. If you would like to join effort, you think you have a possibly related problem, or you simply want to chat on semi-relevant issues, feel free to contact me. Even if the relation is remote. You may be surprised by my ability to find connections between seemingly unrelated problems, even from completely different fields. Even if I cannot find such relations I am always game for stimulating discussions.

Current interests

  • Physics of granular and cellular materials:
    Ever wondered why hour-glasses use sand rather than water? Why it gets wet around your foot when you walk on the beach close to the water line? Why sometimes salt will not pour out of the wretched shaker? Why landslides and snow avalanches occur? These are a few of the questions that interest me in this line of research. I study the way that stresses are transmitted in systems made of discrete particles, regardless of the size. There are quite a few surprises here; some recent insight coming out of this study defy concepts that we are brought up on in highschool. This work is relevant to many industries: powders, grain transport, mechanical and flow properties of sand, colloidal suspensions, stress transmission in cellular systems and solid foams and more.
  • Pullout of single polymer and protein chains, polymer dynamics near the glass temperature and implications to polymer science and protein folding:
    A great deal of effort has been devoted recently to understanding experiments of pulling single polymer and biological molecules and measuring the forces involved. These experiments reveal a very rich behaviour and one usually aims to understand from the force fluctuations the structure of the molecule or the dynamics of the pulling process. Understanding these dynamics, however, gives insight into many phenomena in polymer and protein science. I have constructed a theoretical model to understand the dynamics of such processes in the vicinity of the glass transition temperature. I currently explore the implications of my model on viscosity measurements in this regime, with the rather ambitious goal of trying to bridge between the melt- and glass-based models for polymer dynamics. This model also has direct implications for resistance of polymeric materials to failure at interfaces,plastic deformation of polymer glasses, strength of welded and grafted polymers, and relaxation of single molecules. Efforts to test these ideas experimentally are under way. I am further interested in the application of my model to the pullout of protein chains. There are currently several groups in the world using an Atomic Force Microscope setup to measure the forces needed to unfold particular molecules with the aim to understand from these experiments how proteins are structured. I am keen on applying my model to understand these experiments and hopefully to correctly interpret the force signatures so as to extract information, not only on the protein structure, but also on the relevance of the unfolding dynamics to the folding process of the particular proteins and to protein folding in general.
  • Stress transmission and yield flow in granular media and colloidal suspensions:
    This work is fundamental in that it goes completely outside the paradigm of conventional elasticity and elastoplasticity theories. It is relevant to powders, grain transport, mechanical and flow properties of sand, colloidal suspensions and more. We have formulated a first principles theory for the mesoscopic equations of stress transmission. For some systems, these equations are straightforward to upscale to the macroscopic regime (the holy grail in many fields of science and engineering), but in other systems this is difficult due to effects similar to frustration in glassy systems. The work is carried out both theoretically and experimentally (My first ever experiment!). I have recently found that the same theory applies to cellular solids and, moreover, that it actually pulls the rug from under many respectable analyses in conventional textbooks.
  • Moving curves in 3d and nonlinear dynamics of domain-wall solutions:
    This fundamental study is relevant to a wide range of problems: geometric phases, spin chains (eg, the one dangling from your cursor is an example of a ferromagnetic spin chain with one domain wall marked by the ball), protein dynamics, and domain formation in thin magnetic layers? I have some very intriguing results but hardly any time to build up a detailed file here. If you are very interested I will send you a list of my recent papers on the subject.

Past (but lingering) interests

  • Mesoscale modelling and coarse-graining for use in numerical methods.
  • Slow and fast cracking, and the rough surfaces that these result in.
  • Characterization of hierarchical and fractal patterns beyond simple scaling.
  • Theory for evolving unstable interfaces in Laplacian fields.
  • Properties of strongly nonlinear and inhomogeneous/textured media - This is an old flame which is silently burning and waiting for an opportunity to erupt again.
  • Electromagnetic waves in strongly nonlinear media.