Fereydoon Taheri | Searcharxiv

arXiv2026

Brillouin Spectroscopy Reveals Mechanical Properties Beyond Hydration

Brillouin light scattering is a noncontact technique for probing the micromechanical properties of cells and tissues through the GHz-frequency longitudinal modulus. Interpreting Brillouin spectra in hydrated biological materials remains challenging because the Brillouin shift is influenced not only by water content but also by polymer network mechanics, relaxation processes, and viscous dissipation. Here, we investigated two model hydrogels with distinct network chemistry, together with a binary solvent mixture, to disentangle these contributions. Time- and space-resolved measurements of a hydrating hydrogel further show that Brillouin microscopy captures local mechanical changes that bulk rheometry only partially resolves. Experiments on ethanol-water mixtures further demonstrate that the Brillouin shift does not vary monotonically with hydration but instead reflects changes in the mixture's mechanical properties. In addition, by comparing longitudinal, bulk, and shear viscosities, we identify bulk viscous dissipation as an important contributor to the Brillouin response. Together, these results show that hydration modulates Brillouin spectra but does not fully determine them. Our findings provide a mechanical framework for interpreting Brillouin measurements in hydrated and biomolecular systems.

physics.optics↗

arXiv2022

Towards a robust criterion of anomalous diffusion

Anomalous-diffusion, the departure of the spreading dynamics of diffusing particles from the traditional law of Brownian-motion, is a signature feature of a large number of complex soft-matter and biological systems. Anomalous-diffusion emerges due to a variety of physical mechanisms, e.g., trapping interactions or the viscoelasticity of the environment. However, sometimes systems dynamics are erroneously claimed to be anomalous, despite the fact that the true motion is Brownian -- or vice versa. This ambiguity in establishing whether the dynamics as normal or anomalous can have far-reaching consequences, e.g., in predictions for reaction- or relaxation-laws. Demonstrating that a system exhibits normal- or anomalous-diffusion is highly desirable for a vast host of applications. Here, we present a criterion for anomalous-diffusion based on the method of power-spectral analysis of single trajectories. The robustness of this criterion is studied for trajectories of fractional-Brownian-motion, a ubiquitous stochastic process for the description of anomalous-diffusion, in the presence of two types of measurement errors. In particular, we find that our criterion is very robust for subdiffusion. Various tests on surrogate data in absence or presence of additional positional noise demonstrate the efficacy of this method in practical contexts. Finally, we provide a proof-of-concept based on diverse experiments exhibiting both normal and anomalous-diffusion.

cond-mat.stat-mech↗