Membrane hydrodynamics is intriguing due to an interplay of dimensionalities; momentum travels in the plane of the membrane at short distances, but moves through the outer fluid at larger ones, showing a crossover from 2D to 3D like behavior. Chemical reactions on the surface of a cell, therefore, require a special treatment. While it is possible to perform a simple Smoluchowski-like calculation in 2D to predict reaction rates in membranes, we will see that the expected rates are reduced by an order of magnitude when accounting for hydrodynamic interactions between reactants and targets.
Enrico Fermi was one of the 20th century’s greatest physicists and the only one to reach the professions greatest heights as both a theorist and experimentalist. This talk will describe Fermi’s life and the manner in which his contributions to almost every field of physics came about. Gino Segre` is an emeritus professor of physics and astronomy at the University of Pennsylvania. He received his A.B. from Harvard in 1959 and his Ph.D from M.I.T. in 1963.
In this talk, I will emphasize the ways that physical formulation and insight guide the discovery of new materials, enhancing data-driven approaches. Specific examples will include the advancement of bulk photovoltaics and topological semimetals. The interlocking roles of symmetry, band topology, defects, electron counting, dimensionality crossover, and nanoscale patterning will be developed, and the connection of these phenomena with data searching techniques will be explained.
Cosmic rays are the most energetic particles in the Universe. They reach us at nearly the speed of light mostly from outside the Solar System. They encode the information on their origin and on the matter encountered in their journey to the Earth. Even though their discovery dates back to more than 100 years ago, cosmic-ray origin and transport are far from being understood.
More than 100 years after the discovery of cosmic rays we still know little about the origin of the most energetic particles in the universe. These cosmic particles are mainly atomic nuclei which are accelerated by nature to energies far beyond the reach of human-made accelerators. The highest energy particles seem to originate from other galaxies, but neither these extragalactic sources nor the most energetic sources in our galaxy, the Milky Way, are known.
Cosmic rays, high energy particles originating from outside of the solar system, are believed to be dominated by particles from our Galaxy at least up to the energy of 10^15 eV. Since the discovery of these particles in 1912, the origin, acceleration and propagation of these high energy particles have remained as century old questions. In the last few years, new results from space-borne experiments, such as the rise of the positron flux and hardening of the light nuclei, have begun to challenge our understanding of these particles.
The field of multi-messenger astrophysics is being born. The IceCube Neutrino Observatory at the South Pole plays a role by detecting neutrinos and cosmic rays produced in the most extreme environments in the universe. We aim to understand these environments by studying different kinds of radiation emitted by them. IceCube has measured a flux of neutrinos of astrophysical origin, although their sources remain unidentified. We also study the flux of cosmic rays, its composition and its arrival directions.