לוח שנה משולב

Chirality or handedness is one of the deepest and most persistent mysteries in the sciences, from the molecular asymmetry of life’s building blocks to the emergence of homochirality in early prebiotic systems. Why is chirality “contagious, ” as when a tiny fraction of chiral dopant induces cholesteric twist in an achiral nematic? What mechanisms can spontaneously break mirror symmetry in systems composed entirely of achiral molecules? These questions lie at the intersection of physics, chemistry, and the origins of life. Using the tools of statistical physics, we explore a mechanism that focuses on the role of intramolecular degrees of freedom, in which achiral molecules switch between degenerate configurations of opposite handedness. Theoretical analysis predicts a phase diagram featuring a spatially segregated cholesteric phase with alternating domains of left- and right-handed chiral twist, alongside racemic nematic and isotropic phases. Our model also demonstrates how chiral molecular fluctuations influence the helical twisting power of dopants in the nematic phase. Monte Carlo simulations validate the predicted phase diagram and reveal pattern formation and coarsening in the segregated cholesteric phase. These results suggest that molecular fluctuations between degenerate chiral configurations may be a common mechanism driving cooperative chiral order in soft materials composed of achiral molecules.FOR THE LATEST UPDATES AND CONTENT ON SOFT MATTER AND BIOLOGICAL PHYSICS AT THE WEIZMANN, VISIT OUR WEBSITE: https://www.bio  

Financial systems are becoming increasingly digital and decentralized, demanding a practical fusion of distributed systems security and economic theory. A key enabler of this change, blockchain technology, promises more private and egalitarian economic mechanisms, built by facilitating consensus between pseudonymous actors. However, the theoretical security of these systems may mask significant real-world risks. In this talk, I will present recent advances in bridging this gap between theory and practice. First, I will discuss the resolution of a decade-old puzzle: the lack of observed attacks on major consensus mechanisms. I will then distill the lessons learnt into a holistic approach to designing robust mechanisms for distributed pseudonymous systems and demonstrate its adoption in practice using several lines of work.

We introduce first-passage resetting, in which a diffusing particle is reset to its starting point whenever it reaches a specified threshold.  We present two applications of this mechanism: (1) Optimization in a finite domain, in which a cost is incurred whenever the diffuser is reset to the origin and a reward is given when the particle stays near the reset (maximal performance) point. We derive the condition to optimize the net reward minus the net cost.  (2) We also explore consequences of first-passage resetting in a toy model of wealth sharing to try to determine whether altruism or selfishness is the optimal strategy.

Enzymes are usually described through local active-site chemistry. Yet many catalytic cycles recruit global motion that spans the protein fold. This talk traces a physical chain from sequence to function: internal dynamics generate deformation; deformation sharpens specificity; strain carries force across the fold; viscoelasticity sets the operative timescale; and proteins tune one another’s activity. The result is a physical picture in which enzymes act as sequence-encoded viscoelastic machines, with catalysis coupled to mechanics.