YPF 2020 - Interdisciplinary physics with a focus on biophysics and geophysics
19th & 20th September 2020
Online
This year, the Young Physicists Forum event was organized online during the weekend of the 19th and 20th September 2020. First planned to take place in Bern in April, we had to postpone it and finally chose to do it as an online event for 2020 due to the COVID-19 pandemic.
The topic chosen was “Interdisciplinary physics with a focus on biophysics and geophysics”. There were in total eight lectures with two one-hour lectures per half-day. After each conference, a short questions/answers session with the lecturer took place. Between fifteen and twenty-five people participated to the event. Some of the participants attended all lectures, while some others just attended a few. The registration was open from early September to the day before the Forum on our website. Students from Swiss universities learned about the Forum through their respective student associations. We thank them for having shared our information email with the students.
The Saturday was about the physics of life sciences: biophysics (three lectures) and particle physics’ applications in medical physics (one lecture). The Sunday was focused on the physics of earth sciences with geophysics (three lectures) and physical oceanology (one lecture). Our lecturers are professors in several Swiss universities: EPFL/University of Lausanne, ETHZ, University of Basel, University of Bern and University of Geneva.
On the Saturday morning, after a welcome speech by the YPF committee, the Forum started with a biophysics lecture, “The Dynamics of Life” by Prof. Karsten Kruse (UniGe). Life exists at various scales and shapes, and even if living systems differ largely from non-living matter, they still obey the laws of physics. Hence physics can be used to understand the working principle of such life forms or life components. For example, we saw during the lecture that some protein (Min-protein) patterns are the results of processes of diffusion and of chemical reactions. Another example that was developed is about the length of neuronal axons (the nerve fiber). A neuron senses the length of its axon by using the oscillation of molecular motors, whose frequency is length dependent (this mechanism is illustrated in fig. 1). These are some examples of theoretical biophysics problems Prof. Kruse and his team are working on in Geneva.
The next lecture focused on particle physics’ applications in medical physics, “Multi-disciplinary Research Activities at the Bern medical Cyclotron”, by Prof. Saverio Braccini (UniBe). The use of particle physics in medical diagnostics dates from the late 19th century with radiography, only one month after the discovery of X-rays (the first radiography is the well-known left hand of Wilhelm Röntgen’s wife, Anna). But the X-rays can also be generated directly in the human body, e.g. in the case of a cancer, in a tumor, by attaching a radioactive element to the tumor, like 18 F, led to emit a positron, generating two 511 keV photons by annihilation with an electron. These photons are both ionizing and serving for tumor localization by PET, Positron Emission Tomography. With a strong ionizing isotope, it is even possible to destroy the tumor. When the same method is used for the diagnostics and for the therapy, it is called theranostics. Prof. Braccini and his team are working with the Bern medical cyclotron on future techniques of theranostics. A few weeks after the Forum, the committee had the opportunity to visit this cyclotron in Bern (see fig. 2).
After a lunch break, the afternoon started with a second lecture on biophysics, “Biomimetic validation of biological function” by Prof. Roderick Lim (UniBas). Prof. Lim and his team are working on nanobiology, by developing new biophysical methods to understand interactions that give biological functionality.
The first day ended by a lecture of Prof. Henning Stahlberg (EPFL and UniL): “Versatile applications of Cryo-Electron Microscopy for pharmaceutical drug research: A road map for further developments of an already revolutionary technology”. We had a first view on Cryo-electron microscopy (electron microscopy on a biological sample cooled to a cryogenic temperature), which has revolutionized the structural biology. This microscopy has an atomic resolution, it can then determine proteins structures, a very important issue in biology. However, cryo-electron microscopy still has some limitations regarding resolution and speed. Prof. Stahlberg and his team are working on further developments to reduce samples volumes and increase speed and resolution. They are also working at the Dubochet Center for Imaging, a joint research center shared by the University of Geneva, the University of Lausanne, and the EPFL.
For the second day, the topic was focused on earth sciences. The first lecture was dedicated to ocean physics: “Ocean extremes: From marine heatwaves to ocean biogeochemical extremes”, by Prof. Thomas Frölicher (UniBe). The ocean covers 71% of the Earth surface and has therefore a central role in the climate system. Its temperature is yet increasing. We are able to measure the temperature and its evolution thanks to a network of so-called Argo floats all over the oceans (3916 at the Forum’s day). The heatwaves (increase of temperature over the season’s normal for a certain period) are yet more frequent and longer than before. The most recent heatwaves are even 20 times more likely to occur in present-day climate, with global warming, than in preindustrial climate. The locations of the most important heatwaves over the last two decades are shown on the map of fig. 3. Further, the evolution of oceans’ acidification and deoxygenation is studied by Prof. Frölicher and his team by simulations of their evolution.
For our first lecture about geophysics, we listened to Prof. Andrew Jackson (ETHZ) on the “Theory of the geodynamo: A century of struggle and a new dawn”. The generation of the magnetic field of our planet relies on very complex systems. It is caused by a dynamo effect, which in turn is caused by convection movements of the liquid iron circulating in the outer core (Joseph Larmor was the first one to suppose this, in 1919). The basic equations are known and simulations agree with observations on a large scale. But the experimental reproduction of such a dynamical effect in the laboratory is still a difficult task. The effects on small scales are also not yet fully understood. Prof. Jackson and his team are working about simulating and observing (e.g. with satellites) the planet's magnetic field at ETHZ.
After lunch we attended to the second geophysics lecture about: “Plate tectonics, mantle convection and the long-term evolution of terrestrial planets and moons”, by Prof. Paul Tackley (ETHZ). Tectonic motion is observed, but what is the mechanism? There is convection of hot matter from the depths of the Earth mantle to the surface. The mantle is a solid, but also acts as a fluid with a very high viscosity. It is possible to model a sphere with continents, which fits pretty well the observations on Earth. However, long-term evolution is hard to predict because of the complexity of the system: the fluid dynamics is global but depends on local evolution. Prof. Tackley and his team are working on simulating the formation, evolution and present-day dynamics of the mantle of planets and moons.
The last (but not the least) lecture of the 2020 YPF was given by Prof. Johan Robertsson (ETHZ) about: “Generalized sampling and gradiometry: Changing the rules of the information game”. Gradiometry is the measurement of local gravity acceleration. During the lecture, we learned about some basics of information theory. The development of better techniques to sample the Earth crust is important to gain more information and a better understanding of environmental geophysics. Prof. Robertsson and his team are working on data acquisition, imaging and characterization methods in order to improve the understanding of geophysical processes.
This online 2020 edition of the YPF was evidently a strange one, without discussions between participants nor laboratory visit. We were pretty lucky for not having had any technical problem during the lectures. Despite these strange conditions, our lecturers were happy of their participation and the students were also interested in the topics as shown by the many questions. I personally think this event highlighted the universalism of physics and of physical techniques in sciences. We learned about some topics that are pretty far from the typical physics courses at the university, but that need physics to be understood. After the Forum, we offered some boxes of delicious chocolates to our lecturers to thank them for their very exciting lectures. We hope that the participating students had pleasure and learned a lot from these stimulating introductions to various topics in interdisciplinary physics.
This review was first published in SPS Communications No. 63, February 2021
This year event was made possible thanks to the collaboration of:
