Internal Seminar Series

Dr. Oliver Bellwood, Quantum Engineering and Design Unit

Snakes are mediocre at quantum physics - but is this a surprise?

The difficulty in studying quantum magnetism is highly dependent on the number of spatial dimensions considered. In one dimension, both analytic and numerical methods allow us to extract physical quantities with high accuracy. In three dimensions, where quantum fluctuations can be treated as minor corrections within a semiclassical approach, mean-field and spin-wave theories are typically sufficient. However, in two dimensions the semiclassical theories often breakdown, yet the one dimensional methods do not readily generalize. An important exception is the powerful Density Matrix Renormalization Group (DMRG) algorithm; despite being explicitly one dimensional it can be used in two dimensions by identifying a bijective mapping between the dimensionalities. The most common mapping is the one that spans the lattice in a row-by-row fashion - the well known 'snake' path. Although this mapping is very natural it raises a question: is this mapping optimal? In this talk I will discuss how DMRG with the snake path is outperformed by a class of mappings, the self-similar fractal Hamilton paths, when studying the square lattice Heisenberg antiferromagnet.

Dr. Alberto Sassi, Biological Complexity Unit

How do bacteria know when to replicate DNA?

Through billions of years of evolution, bacteria have optimized their strategy for DNA replication in such a way that their genome is copied very quickly and accurately. In particular, in fast growth conditions, many bacteria manage to grow and divide in a faster time than it would take to fully copy the entire genome from start to finish. They do this by using overlapping rounds of replication (the cell is already replicating DNA not just for its daughters, but for the grand-daughters as well). For this strategy to work, the cell must have an accurate mechanism to determine when replication should begin. This timing is determined by a protein called DnaA, which binds to specific motifs in the origin of replication (DnaA boxes), stimulates the separation of the double strands and recruits the helicase. I will discuss the regulatory mechanisms that ensure that DnaA is active and available when the replication is supposed to start, while it is quickly de-activated and sequestered outside of such time window. I will also explain how the spatial organization of DnaA boxes in the origin contributes to the sensitivity and accuracy of replication timing.

Zoom Link: https://oist.zoom.us/j/94007726340 

Note on the alcohol: 

From fall 2024, we offer beer along with other refreshments. This is paid for privately by generous faculty and representatives. Behave responsibly, don't ruin it, and never drink and drive. Ishikawa Taxi (098-972-5406) and Agachi Daiko (080-6485-9978) are always available.