Kontakt: Rainer-G. Ulbrich

Kontakt: Rainer-G. Ulbrich

Kontakt: Rainer-G. Ulbrich

Statistical mechanics has provided a powerful tool for understanding the states of thermodynamic matter, and it is intriguing to investigate whether these successes are also relevant to non-equilibrium systems such as granular materials. I will describe experiments on a two-dimensional dense granular gas of disks suspended on a horizontal air table and agitated at the boundaries. We measure both bulk and particle-scale dynamics, and find a number of thermal-like behaviors including diffusive dynamics, a granular Boyle's law with a van der Waals-like equation of state, and energy equipartition for rotational and translational degrees of freedom. However, the scarcity of free volume provides a crucial control on the dynamics, and each of the above thermal-like behaviors is accompanied by interesting caveats.

Kontakt: Rainer-G. Ulbrich

Kontakt: Rainer-G. Ulbrich

Kontakt: Rainer-G. Ulbrich

Kontakt: Rainer-G. Ulbrich

Kontakt: Rainer-G. Ulbrich

Kontakt: Rainer-G. Ulbrich

Kontakt: Rainer-G. Ulbrich

Kontakt: Rainer-G. Ulbrich

Two seemingly conflicting properties of native proteins, such as enzymes and antibodies, are known to coexist. While proteins need to keep their specific native fold structure thermally stable, the native fold displays the ability to perform large amplitude motions that allow proper function. This conflict cannot be bridged by compact objects which are characterized by small amplitude vibrations and by a Debye density of low frequency modes. Recently, however, it became clear that proteins can be described as fractals; namely, geometrical objects that possess self similarity. Adopting the fractal point of view to proteins makes it possible to describe within the same framework essential information regarding topology and dynamics using three parameters: the number of amino acids along the protein backbone N, the spectral dimension and the fractal dimension. The fractal character implies large amplitude vibrations of the protein that could have led to unfolding. We showed that by selecting a thermodynamic state that is “close” to the edge of stability against unfolding, nature has solved the thermostability conflict. Starting off from a thermal marginal stability criterion we reached a universal equation describing the relation between the spectral and fractal dimensions of a protein and the number of amino acids. Using structural data from the protein data bank (PDB) and the Gaussian network model (GNM), we computed and for about 5,000 proteins(!)and demonstrated that the equation of state is well obeyed. Proteins have been shown to exhibit anomalous dynamics. The anomalous behavior may, in principle, stem from various factors affecting the energy landscape under which a protein vibrates. We focused on the structure-dynamics interplay and showed how the fractal-like properties of proteins lead to such anomalous dynamics. We used diffusion, a method sensitive to the structural features of the protein fold and them alone, in order to probe protein structure. Conducting a large scale study of diffusion on........

Kontakt: Rainer-G. Ulbrich