Recent eLife article on plankton tracking gets featured on Swedish national radio

Planktons imaged under a holographic microscope. (Illustration by J. Heuschele.)
The article Microplankton life histories revealed by holographic microscopy and deep learning gets featured on Vetenskapradion Nyheter (Science radio) operated by Sveriges Radio (Swedish national radio) on November 7, 2022.

The short audio feature (Hologram hjälper forskare att förstå plankton) which highlights the important results of the paper (in Swedish) is now available for public listening.

Vetenskapradion Nyheter airs daily news, reports and in-depth discussions about latest research.

Press release on Tunable critical Casimir forces counteract Casimir-Lifshitz attraction

An illustration of microscopic gold flakes on surface. (Image by F. Schmidt.)
The article Tunable critical Casimir forces counteract Casimir-Lifshitz attraction has been featured in the News of the University of Gothenburg (in English and in Swedish), SISSA-International School of Advanced Studies in Trieste, Italy, Heinrich-Heine-Universität Düsseldorf, and Friedrich-Schiller-Universität Jena.

The study, published in Nature Physics and co-written by researchers at the Soft Matter Lab of the Department of Physics at the University of Gothenburg, demonstrate that tunable repulsive critical Casimir forces can be used to counteract stiction, i.e., the tendency of tiny parts of micro- and nanoelectromechanical devices to stick together, which is caused by the Casimir-Lifshitz interaction.

The study is featured also in Phys.org, NanoWerk.

Here the links to the press releases:
Casimir vs Casimir – using opposing forces to improve nanotechnology (GU, English)
https://www.gu.se/nyheter/casimir-vs-casimir-klaschande-krafter-kan-forbattra-nanotekniken (GU, Swedish)
Casimir vs Casimir – usare forze opposte per migliorare le nanotecnologie (SISSA, Italian)
Casimir vs Casimir – using opposing forces to improve nanotechnology (SISSA, English)
Nano-Bauteile clever voneinander lösen (Heinrich-Heine-Universität Düsseldorf)
Clever method for separating nano-components (Friedrich-Schiller-Universität Jena)
Clever method for separating nano-components (Phys.org)
Clever method for separating nano-components (NanoWerk)

Tunable critical Casimir forces counteract Casimir-Lifshitz attraction published in Nature Physics

Gold flake suspended over a functionalized gold-coated substrate. (Image by F. Schmidt.)
Tunable critical Casimir forces counteract Casimir-Lifshitz attraction
Falko Schmidt, Agnese Callegari, Abdallah Daddi-Moussa-Ider, Battulga Munkhbat, Ruggero Verre, Timur Shegai, Mikael Käll, Hartmut Löwen, Andrea Gambassi and Giovanni Volpe
Nature Physics 19, 271-278 (2023)
arXiv: 2202.10926
doi: 10.1038/s41567-022-01795-6

Casimir forces in quantum electrodynamics emerge between microscopic metallic objects because of the confinement of the vacuum electromagnetic fluctuations occurring even at zero temperature. Their generalization at finite temperature and in material media are referred to as Casimir-Lifshitz forces. These forces are typically attractive, leading to the widespread problem of stiction between the metallic parts of micro- and nanodevices. Recently, repulsive Casimir forces have been experimentally realized but their reliance on specialized materials prevents their dynamic control and thus limits their further applicability. Here, we experimentally demonstrate that repulsive critical Casimir forces, which emerge in a critical binary liquid mixture upon approaching the critical temperature, can be used to actively control microscopic and nanoscopic objects with nanometer precision. We demonstrate this by using critical Casimir forces to prevent the stiction caused by the Casimir-Lifshitz forces. We study a microscopic gold flake above a flat gold-coated substrate immersed in a critical mixture. Far from the critical temperature, stiction occurs because of dominant Casimir-Lifshitz forces. Upon approaching the critical temperature, however, we observe the emergence of repulsive critical Casimir forces that are sufficiently strong to counteract stiction. This experimental demonstration can accelerate the development of micro- and nanodevices by preventing stiction as well as providing active control and precise tunability of the forces acting between their constituent parts.

Press release on Microplankton life histories revealed by holographic microscopy and deep learning

Planktons imaged under a holographic microscope. (Illustration by J. Heuschele.)
The article Microplankton life histories revealed by holographic microscopy and deep learning has been featured in the news of University of Gothenburg (in English & Swedish) and in the press release of eLife (in English).

The study, now published in eLife, and co-written by researchers at the Soft Matter Lab of the Department of Physics at the University of Gothenburg, demonstrates how the combination of holographic microscopy and deep learning provides a strong complimentary tool in marine microbial ecology. The research allows quantitative assessments of microplankton feeding behaviours, and biomass increase throughout the cell cycle from generation to generation.

The study is featured also in eLife digest.

Here are the links to the press releases:
Researchers combine microscopy with AI to characterise marine microbial food web (eLife, English)
Holographic microscopy provides insights into the life of microplankton (GU, English)
Hologram ger insyn i planktonens liv (GU, Swedish)
The secret lives of microbes (eLife digest)

Seminar by G. Volpe at QSIT, ETH Zurich, 3 November 2022

Active droploids. (Image taken from Nat. Commun. 12, 6005 (2021).)
Experimental study of critical fluctuations and critical Casimir forces
Giovanni Volpe
Invited seminar at QSIT/Quantum Center, ETH Zurich
Thursday, November 3, 2022 – 16:00 – 17:00

Critical Casimir forces (CCF) are a powerful tool to control the self-​assembly and complex behavior of microscopic and nanoscopic colloids. While CCF were theoretically predicted in 1978, their first direct experimental evidence was provided only in 2008, using total internal reflection microscopy (TIRM). Since then, these forces have been investigated under various conditions, for example, by varying the properties of the involved surfaces or with moving boundaries. In addition, a number of studies of the phase behavior of colloidal dispersions in a critical mixture indicate critical Casimir forces as candidates for tuning the self-​assembly of nanostructures and quantum dots, while analogous fluctuation-​induced effects have been investigated, for example, at the percolation transition of a chemical sol, in the presence of temperature gradients, and even in granular fluids and active matter. In this presentation, I’ll give an overview of this field with a focus on recent results on the measurement of many-​body forces in critical Casimir forces, the realization of micro-​ and nanoscopic engines powered by critical fluctuations, and the creation of light-​controllable colloidal molecules and active droploids.

Date: Thursday, November 3, 2022
Time: 16:00
Place: ETH Zurich, Campus Hönggerberg, HPF G 6
Host: Lukas Novotny

Microplankton life histories revealed by holographic microscopy and deep learning published in eLife

Tracking of microplankton by holographic optical microscopy and deep learning. (Image by H. Bachimanchi.)
Microplankton life histories revealed by holographic microscopy and deep learning
Harshith Bachimanchi, Benjamin Midtvedt, Daniel Midtvedt, Erik Selander, and Giovanni Volpe
eLife 11, e79760 (2022)
arXiv: 2202.09046
doi: 10.7554/eLife.79760

The marine microbial food web plays a central role in the global carbon cycle. Our mechanistic understanding of the ocean, however, is biased towards its larger constituents, while rates and biomass fluxes in the microbial food web are mainly inferred from indirect measurements and ensemble averages. Yet, resolution at the level of the individual microplankton is required to advance our understanding of the oceanic food web. Here, we demonstrate that, by combining holographic microscopy with deep learning, we can follow microplanktons throughout their lifespan, continuously measuring their three dimensional position and dry mass. The deep learning algorithms circumvent the computationally intensive processing of holographic data and allow rapid measurements over extended time periods. This permits us to reliably estimate growth rates, both in terms of dry mass increase and cell divisions, as well as to measure trophic interactions between species such as predation events. The individual resolution provides information about selectivity, individual feeding rates and handling times for individual microplanktons. This method is particularly useful to explore the flux of carbon through micro-zooplankton, the most important and least known group of primary consumers in the global oceans. We exemplify this by detailed descriptions of micro-zooplankton feeding events, cell divisions, and long term monitoring of single cells from division to division.

Sex differences in multilayer functional network topology over the course of aging in 37543 UK Biobank participants accepted on Network Neuroscience

Example of the 21 resting-state networks used as nodes and their positive (red) and negative connections (blue) for one of 140 the subjects included in the analyses. (Image by the Authors of the manuscript.)
Sex differences in multilayer functional network topology over the course of aging in 37543 UK Biobank participants
Mite Mijalkov, Dániel Veréb, Oveis Jamialahmadi, Anna Canal-Garcia, Emiliano Gómez-Ruiz, Didac Vidal-Piñeiro, Stefano Romeo, Giovanni Volpe, Joana B. Pereira
Network Neuroscience 1-40 (2022)
doi: 10.1162/netn_a_00286
medRxiv: 10.1101/2022.03.08.22272089

Aging is a major risk factor for cardiovascular and neurodegenerative disorders, with considerable societal and economic implications. Healthy aging is accompanied by changes in functional connectivity between and within resting-state functional networks, which have been associated with cognitive decline. However, there is no consensus on the impact of sex on these age-related functional trajectories. Here, we show that multilayer measures provide crucial information on the interaction between sex and age on network topology, allowing for better assessment of cognitive, structural, and cardiovascular risk factors that have been shown to differ between men and women, as well as providing additional insights into the genetic influences on changes in functional connectivity that occur during aging. In a large cross-sectional sample of 37543 individuals from the UK Biobank cohort, we demonstrate that such multilayer measures that capture the relationship between positive and negative connections are more sensitive to sex-related changes in the whole-brain connectivity patterns and their topological architecture throughout aging, when compared to standard connectivity and topological measures. Our findings indicate that multilayer measures contain previously unknown information on the relationship between sex and age, which opens up new avenues for research into functional brain connectivity in aging.

Invited Talk by G. Volpe at Adaptivity in Nonlinear Dynamical Systems, Potsdam, 23 September 2022

M. xanthus cell-cell and cell-particle local interactions during cellular aggregation.
Feedback between active matter and its environment
Giovanni Volpe
Invited Talk (Online) at the hybrid Workshop: Adaptivity in Nonlinear Dynamical Systems
Potsdam, Germany
23 September 2022, 9:30 CEST

I will present some examples of how feedback cycles can occur between active matter and its environment. In particular, I’ll show the formation of active molecules and active droploids from passive colloidal building blocks; the emergence of non-Boltzmann statistics and active-depletion forces between plates in an active bath; and the environment topography alters the way to multicellularity in the bacterium Myxococcus xanthus.

Keynote Lecture by G. Volpe at ISMC 2022, Poznan, 20 September 2022

An exemplar of Hexbugs, commercially available toy robots that have been used in the experimental demonstration proposed. (Image from arXiv: 2209.04168)
Playing with Active Matter
Giovanni Volpe
Keynote Lecture at ISMC 2022
Poznan, Poland
20 September 2022, 13:30 CEST

In the last 20 years, active matter has been a very successful research field, bridging the fundamental physics of nonequilibrium thermodynamics with applications in robotics, biology, and medicine. This field deals with active particles, which, differently from passive Brownian particles, can harness energy to generate complex motions and emerging behaviors. Most active-matter experiments are performed with microscopic particles and require advanced microfabrication and microscopy techniques. Here, we propose some macroscopic experiments with active matter employing commercially available toy robots, i.e., the Hexbugs. We demonstrate how they can be easily modified to perform regular and chiral active Brownian motion. We also show that Hexbugs can interact with passive objects present in their environment and, depending on their shape, set them in motion and rotation. Furthermore, we show that, by introducing obstacles in the environment, we can sort the robots based on their motility and chirality. Finally, we demonstrate the emergence of Casimir-like activity-induced attraction between planar objects in the presence of active particles in the environment.

Soft Matter Lab members present at ISMC 2022, Poznan, 19-23 September 2022

The Soft Matter Lab participates to the ISMC 2022 in Poznan, Poland, 19-23 September 2022, with the presentations listed below.