Wydział Fizyki UW > Badania > Seminaria i konwersatoria > Soft Matter and Complex Systems Seminar

Soft Matter and Complex Systems Seminar

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Zapraszamy do sali 1.40, ul. Pasteura 5 o godzinie 09:30

Joanna Piotrowska (California Institute of Technology)

What Black Holes Remember: Constraining Their Cosmic Growth with Angular Momentum Measurements

Supermassive black holes are thought to play a central role in shaping the evolution of galaxies, particularly in shutting down star formation in the most massive systems. However, the pathways by which these black holes grow over cosmic time, and how that growth connects to their host galaxies, remain uncertain. A growing body of work combining cosmological simulations and observational surveys indicates that the suppression of star formation is closely linked to black hole activity from the early Universe to the present day. While this connection is now well established, direct constraints on the growth history of supermassive black holes remain limited.
X-ray reflection spectroscopy provides a unique probe of the innermost regions of accretion flows, where strong-gravity effects enable measurements of black hole angular momentum (spin). As a quantity that retains memory of past accretion and merger events, spin offers apowerful observational handle on black hole growth pathways. Recent work has begun to place these measurements in a broader cosmological context by combining spin constraints from X-ray reflection spectroscopy with predictions from galaxy formation models, enabling the first population-level tests of black hole growth scenarios. These efforts move beyond individual objects toward statistical constraints on how supermassive black holes assemble their mass.
The next generation of upcoming X-ray observatories will significantly expand these measurements, enabling a direct link between small-scale accretion physics and the large-scale evolution of galaxies.

Zapraszamy do sali 1.40, ul. Pasteura 5 o godzinie 09:30

Jan Turczynowicz (FUW)

Measurements of biological carbon sequestration in the oceans

The oceans capture a significant portion of human-made CO2. In the upper 100 meters (the euphotic zone), phytoplankton convert this dissolved gas into organic matter, which aggregates into sinking particles known as marine snow. This process, called the biological carbon pump, is a critical mechanism for burying carbon on the seabed. Field observations, described by the Martin curve, show that carbon flux drops rapidly with depth, with only about 10% of this material sinking past 200 meters. However, directly measuring this curve is difficult. While indirect methods using radioactive thorium isotopes are widely popular, they present significant inconsistencies. This talk will discuss the issues surrounding thorium-based estimates and present an alternative method based on oxygen distributions, which shows promising agreement with direct measurements.

Zapraszamy do sali 1.40, ul. Pasteura 5 o godzinie 09:30

Igor Kumela, Jan Kossacki, Jakub Wróbel, Aleksander Syrewicz, Maria Puciata-Mroczynska (FUW)

Student Talks vol. 1

The schedule of talks:

Igor Kumela – Minimalistic particle-based model of cloud chamber
Jan Kossacki – Topological transition in confined ciliary systems
Jakub Wróbel – Bistability in chemical reactors
Aleksander Syrewicz – Physics of flocking
Maria Puciata-Mroczynska – Modelling single grain dynamics on a rough inclined plane

Zapraszamy do sali B0.14, ul. Pasteura 5 o godzinie 11:15

Douglas R. Brumley (University of Melbourne, Australia)

Nutrient transport in dynamic microenvironments

The capacity for organisms to exchange nutrients with one another and their surroundings underpins microbial symbioses, biogeochemical cycling in the ocean, and the healthy functioning of corals. Here, we explore three-dimensional active transport by ciliary arrays around coral surfaces, using a combination of mathematical modelling, non-invasive measurements of ciliary distributions, and quantification of flow fields and spatial oxygen profiles. We also examine how individual bacteria are capable of exchanging nutrients through chemotactic tracking of fine-scale chemical trails exuded by cells and highlight how nutrient transport and chemical partnerships are influenced by fluid flows.

Zapraszamy do sali 1.40, ul. Pasteura 5 o godzinie 09:30

Maciej Matyka (Faculty of Physics and Astronomy, University of Wrocław)

Computational Modelling with Single Prompts

Regardless of how we look at AI large language models (LLMs) - as a massive collection of data from which we can cleverly extract information, as an assistant who can perform simple tasks for us and write simple codes, or perhaps as a machine that randomly selects words, in a sense guided by what it have had has seen in the past - we are undoubtedly witnessing a revolution.In the seminar, I will discuss selected aspects of the use of modern large language models, such as Gemini, Grok, ChatGPT, DeepSeek, and Claude. I will discuss the concept of a single prompt and its use to generate computer code for dozens of models across computational physics, statistical physics, computational fluid dynamics.
I will illustrate the presentation with practical examples from statistical and soft-matter physics and include results of students from the modelling class given by me at the same week at UW.

Zapraszamy do sali 1.40, ul. Pasteura 5 o godzinie 09:30

Emilia Trudnowska (Institute of Oceanology, Polish Academy of Sciences)

Ocean Particles in Motion: Patchiness, Fluxes, and Ecosystem Links from an In Situ Perspective

Particles in the ocean—ranging from microscopic to larger aggregates - marine snow are fundamental carriers of carbon, energy, and ecological interactions. I will present an in situ perspective on those aspects and what are the methodologies and technologies used by oceanographers for direct observations of particles in their natural environment. These include laser counters, underwater vision profilers, sediment traps, and autonomous platforms that resolve particle.

My work has been oscillating around explorations how particle dynamics vary across spatial and temporal scales and the processes that shape particles distribution, transformation, and ecological significance across diverse marine environments: Arctic (Svalbard, Greenland, Barents Sea), Antarctic, sub-Antarctic (Beagle Channel), north Atlantic (Gulf Stream, Norwegian Sea), and Pacific (Monterey Bay). The presented examples of key processes governing particles dynamics include: 1) patchiness, 2) models of secondary production based on size structure, 3) particle–plankton co-existance, 4) classification of particles into morphocategories that reflect their origin and transformation pathways, 5) particle flux and sinking rates in relation to carbon export and ecosystem connectivity, 6) mapping approaches that link particle distributions to food availability for higher trophic levels such as fish and seabirds, 7) the effects of glacier melting o particle pools and transformations, 8) resuspension of particles in kelp forest systems, and 9) seasonal variability in shaping particle abundance and composition.

By integrating observational techniques with process-based understanding, this lecture underscores the importance of particles as a unifying framework for studying marine ecosystems, and aims to stimulate new perspectives for discussion and collaboration.

Zapraszamy do sali 1.40, ul. Pasteura 5 o godzinie 09:30

Jacek Miękisz (MIM UW)

Phase transitions in stochastic evolutionary games on graphs

Short abstract, general discussion

We discuss similarities and differences between systems of interacting spins in the ferromagnetic Ising model and systems of interacting players in evolutionary games. We compare Nash equilibria to ground states and phase transitions in both models.

Long abstract, a case study

We examine the impact of the maintenance cost of social links on cooperative behavior in the Prisoner’s Dilemma game on the Barabási-Albert scale-free network with a pairwise stochastic imitation. We show by means of Monte Carlo simulations and pair approximation that the cooperation frequency changes abruptly from an almost full cooperation to a much smaller value when we increase the cost of maintaining links. In the critical region, the stationary distribution is bimodal and the system oscillates between two states: the state with almost full cooperation and one with coexisting strategies. We show that the critical region shrinks with the increasing size of the population. However, the expected time the system spends in a metastable state before switching to the other one does not change as a function of the system’s size, which precludes the existence of two stationary states in the thermodynamic limit of the infinite population.

Bibliography

J. Miękisz and J. Mohamadichamgavi, Phase transitions in the prisoner’sdilemma game on the Barabási-Albert graph with participation cost, Phys.Rev. E 112: L032302 (2025).
https://www.mimuw.edu.pl/~miekisz/phtrpre.pdf

J. Miękisz, J. Mohamadichamgavi and J. Łacki, Phase transitions in thePrisoner’s Dilemma game on scale-free networks, BioPhysMath 1: 9 pages(2024).
https://www.mimuw.edu.pl/~miekisz/phasetrpdbpm.pdf

Zapraszamy do sali 1.40, ul. Pasteura 5 o godzinie 09:30

Marcin Napiórkowski (KMMF FUW)

Bose-Einstein condensation: an ongoing mathematical challenge

Proving Bose-Einstein condensation in the thermodynamic limit remains a major open problem in mathematical physics. In my talk, I will explain the content of the conjecture and review recent progress in the study of bosonic many-body systems.

Zapraszamy do sali 1.40, ul. Pasteura 5 o godzinie 09:30

Rafał Błaszkiewicz (IFT UW)

Unsteady Effects in Cilia-Mediated Transport and Microscale Mixing

Authors:
Rafał Błaszkiewicz¹, Margot Young², Albane Théry², Talia Becker Calazans², Arnold J.T.M. Mathijssen², Maciej Lisicki¹

¹University of Warsaw, Warsaw, Poland
²University of Pennsylvania, Philadelphia, USA

Cilia are key drivers of fluid transport in biological systems, from single-celled organisms to human tissues. Traditional models often treat ciliary flows as steady, yet the beating of cilia is inherently unsteady, generating flows that evolve on timescales comparable to viscous diffusion.
In this work, we use a time-dependent linear Stokes framework with Green’s functions and memory kernels to model flows generated by individual and coordinated cilia motion, represented by point-like “Pufflets.” Combining theory, simulations, and experiments, we examine how unsteady actuation affects particle trajectories and flow structures.
Our results show that unsteady effects can modify transport pathways and influence mixing at the microscale, particularly when multiple cilia interact. These findings highlight differences between steady and unsteady Stokes flows and provide insight into the mechanisms underlying cilia-mediated fluid transport.

The full study is available at: https://doi.org/10.48550/arXiv.2603.11020.

Zapraszamy do sali 1.40, ul. Pasteura 5 o godzinie 09:30

Jonasz Słomka (FUW)

How encounters at the microscale prime microbial interactions

Microbial interactions often critically depend on the rate of physical cell-cell or cell-resourceencounters. In a liquid environment, many prominent examples include encounters amongphytoplankton in the ocean that lead to the formation of marine snow, the formation of livingaggregates by cyanobacteria, bacterial chemotaxis towards leaky phytoplankton, andhorizontal gene transfer between bacteria. Microscale encounters are nearly alwaysquantified as encounters between inanimate spheres, borrowing from the physics of gases,coagulating colloids, and rain formation. However, these classical approaches often fail toaccount for important traits of microorganisms, such as cell elongation, motility, or gradientsensing. Even more importantly, experimental assays typically do not control cell-cellencounters. In my talk, I will outline how more realistic models of encounters at themicroscale can contribute to our understanding of fundamental ecological processescontrolled by microbes, from active aggregation through chemotaxis to gene exchanges. Iwill close by presenting our recent experimental evidence that encounters driven by fluidshear strongly control the rates of horizontal gene transfer between bacteria.

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