The Friday Physics Colloquia at the Department of Physics are open to all. An important goal for the colloquia is to be a meeting place between faculty and students to learn about interesting developments in physics. Undergraduate students are especially encouraged to attend. Speakers are asked to keep the talks at a level targeting a master student in physics.

In the spring semester 2022, colloquium lectures start at 13:15 CET. Lectures are presented in either physical seminar or webinar formats according to the speaker's desire and the pandemic situation. Seminars are held in R10 and webinars are live streamed via Zoom platform.

Spring 2022 schedule

April 1st @ 13:15

Title: Liquid Crystals from Trees
Speaker: Maria Helena Godinho
Soft and biofunctional materials group, NOVA University Lisbon, Portugal
Place: R10
Abstract: Cellulose nanocrystals (CNCs) are very well known to form aqueous colloidal lyotropic liquid crystalline phases in water [1]. The colloidal liquid crystalline system is due to the rod shape of the CNCs. The formation of colloidal liquid crystals in aqueous solutions was first report for rod-like tobacco mosaic virus solutions [2] and in 1949, Onsager [3] used entropic arguments to explain the formation of a nematic phase from an isotropic phase of rods. For CNCs, in addition to the nematic phase, a cholesteric structure was also reported [4]. The formation of tactoids from an isotropic phase was found to be at the genesis of a high-density cholesteric phase that deposits at the bottom of the vials. Here, we will discuss the coexistence of a nematic phase with an isotropic phase, at the isotropic-nematic phase separation, in CNCs aqueous suspensions extracted from different sources. Our work opens new horizons on the preparation of liquid crystalline phases from CNCs aqueous suspensions.

References
[1] M.H. Godinho, Science 369 (2020) 918.
[2] F. C. Bawden, N. W. Pirie, J. D. Bernal, I. Fankuchen, Nature, 138, 1051 (1936).
[3] L. Onsager, Ann. N. Y. Acad. Sci. 51, 627 (1949).
[4] S.N. Fernandes et al., Adv. Mat., 29(2), 1603560 (2017).

April 22nd @ 13:15

Title: Who, how, and why? Navigating physics studies from students’ perspectives
Speaker: Anders Johansson
Engineering Education Research, Chalmers University of Technology, Sweden
Place: R10
Abstract: Studying physics at university is not an obvious choice for most young people today. Navigating further choices, classes, and the culture of the subject can present as challenges to those embarking on the journey of an education in physics. How can we understand these processes in order to help students succeed, and how do we remedy the imbalanced recruitment to physics educations?
My research is situated within a recent tradition in physics education that highlights the need for sociocultural approaches to these problems, that is, analyzing students’ experiences and the education in cultural terms. In the presentation, drawing from my research, I will talk about: how quantum mechanics may serve as an inspiration to study physics for some (but not all) students, but how this can turn into disappointment and disillusion at the university; how master’s students in physics need to navigate norms of intelligence and nerdiness in relation to their choices; and the various resources students from underrepresented groups have used to be able to partake and persist in physics.

April 29th @ 13:15

Title: Physical and medical acoustics: Bubbles, drops and nanoparticles
Speaker: Michel Versluis
Physics of Fluids Group, University of Twente, The Netherlands
Place: R10
Abstract: The acoustic excitation of bubbles and droplets has widespread use in medical technology and nanotechnology applications. These include bulk and surface acoustic waves for bubble and droplet production, as well as bubble and droplet actuation to perform local drug delivery or local and well-controlled surface cleaning. For example, the controlled jet breakup of droplets can be accelerated through the resonant acoustic excitation of instable modes on the jet to form monodisperse droplets at a uniform production rate. Beat frequencies can be exploited to form larger droplet constructs through well-controlled coalescence in flight to be used to efficiently generate extreme ultraviolet wavelengths for the next-generation nanolithography machines. Acoustically driven bubbles can promote efficient mixing on the microscale through acoustic streaming and stable cavitation. Microbubbles can be acoustically driven to quantify organ perfusion and low-boiling point nanodroplets can also be decorated with a payload of nanoparticles which carries great potential for their use as drug delivery agents in the context of personalized medical therapy. Key to all these emerging applications is a precise acoustic control of the interaction of ultrasound with the bubbles and droplets. The challenge here is the combined microscopic length scales and ultrashort time scales associated with the mechanisms controlling bubble and droplet formation and its activation processes, which we solve by high-resolution ultrafast microscopy, even down to the nanosecond. Together with theoretical modeling and numerical simulations these experiments assist in our in-depth fundamental physical understanding of bubble and droplet behavior, which then provides intriguing new prospects for innovative solutions in nanotechnology industry and in nanomedicine.

May 6th @ 13:15

Title: Quantum heat engines: Geometric properties and collective effects
Speaker: Rosario Fazio
Condensed Matter and Statistical Physics Section, ICTP, Italy
Place: R10
Abstract: Small quantum systems connected to several different thermal reservoirs probably constitute the smallest heat engines one can imagine. Their operating mode may be quite different from their macroscopic counterpart, intimately linked to the dynamics of quantum open systems. Fluctuations and quantum effects, for example, are essential in the characterisation of the performance of the thermal machines. I will give first an overview of the field. Afterwards, I will consider the case of heat engines and refrigerators, operating under periodic adiabatic driving and in contact with thermal reservoirs kept at different temperatures where many observables characterizing this operating mode and the performance of the machine are of geometric nature.  I will then discuss whether collective effects may help to carry enhancements  when increasing the number of constituents composing the working substance of the engine. I will in particular focus on the case  in which the working substance is composed by a system of interacting spins.