12:00 - 12:30 - Walk-in with Pizza
12:30 - 12:50 Janni Harju - PhD Candidate, Physics of Living Systems (Chase Broedersz's group), Vrije Universiteit Amsterdam
Title: How loop-extruders organize and segregate bacterial chromosomes
Abstract: The genomes of many bacterial species consist of a single, circular chromosome, which is concurrently transcribed, replicated, and segregated. How do bacteria organize their chromosomes to allow for these simultaneous processes? I will discuss how loop-extruding motor proteins allow bacteria to organize their chromosomes within the cellular confinement. First, I will explain how loop-extruders can give rise to linear chromosome order by either tying the chromosomal arms together, or by forming loops on a section of the chromosome. Second, I will show how loop-extruders can drive bacterial chromosome segregation by changing the large-scale topology of the chromosome. These examples illustrate how bacteria use polymer physics-based mechanisms to ensure the faithful segregation of their genomes.
12:50 -13:45 Dr. Dr. Jeroen Koelemeij, Quantum Metrology and Laser Applications, Department of Physics & Astronomy, Vrije Universiteit Amsterdam
Title: Measuring time, distances, and quantum particle properties with atomic clock networks
Abstract: The power of atomic clocks and precise time measurement is illustrated by Global Navigation Satellite Systems (GNSS), which enable positioning, navigation and timing (PNT) services on Earth. Billions of people use GNSS-powered navigation apps on their smartphones, and GNSS receivers are widely used to synchronize equipment in datacenters, mobile networks, and the electrical power grid. Yet, GNSS have their limitations. They are vulnerable to solar flares, radio jammers, and space weapons, and while GNSS distributes atomic time with high accuracy, the accuracy is insufficient for demanding (scientific) applications.
His research at VU Amsterdam aims to overcome the limitations of GNSS by integrating atomic clocks into fiber-optic telecommunications infrastructure. In his presentation, he will show how such a local atomic clock network at VU enabled accurate measurements of vibrational frequencies in single, isolated molecular ions [1], which today form the basis of reference value of the electron mass [2,3]. He will also present results of a collaboration with Delft University of Technology and SURF, in which we demonstrated decimeter-level positioning and sub-nanosecond time distribution via a mobile-network-like infrastructure that was synchronized to the atomic clocks at VSL Delft [4].
His research at VU has also led to various spin-off activities such as the enterprise OPNT BV, who recently designed and helped roll out the national SURFtime&frequency network [5]. And with support from the QuantumDeltaNL national growth fund, VU has become involved in the development of synchronization technology for future quantum and PNT networks [6], as well as European networks of optical clocks that are sensitive enough to detect centimeter height differences over continental distances via the gravitational redshift. He will show how these and other developments in the field point to an imminent paradigm shift towards (quantum) telecommunication networks that will open up new avenues for scientific research and engineering, while providing enhanced PNT services that are complementary to GNSS, thus reducing the societal risks of GNSS outage.
- S. Patra et al., Science 369, 1238 (2020).
- J.-Ph. Karr & J.C.J. Koelemeij, Mol. Phys. 121, e2216081 (2023).
- P. Mohr et al., ‘CODATA recommended values of the fundamental constants’, arXiv:2409.03787v1 [hep-ph] 30 Aug 2024; https://pml.nist.gov/cgi-bin/cuu/Value?meu|search_for=electron+mass .
- J.C.J. Koelemeij et al., Nature 611, 473 (2022).
- https://www.surf.nl/en/themes/network/surf-timefrequency-pilot .
- J.C.J. Koelemeij et al., NATO STO-MP-IST-SET-198-B1-02 (2024).