Seminar by B. Roy, 24 May 2023

Basudev Roy.
Study of out-of-plane rotations in optical tweezers and applications in soft matter and biological systems
Basudev Roy
Indian Institute of Technology Madras, India
Date: 24 May 2023
Time: 12:30
Place: Nexus

Abstract:
A rigid body can have 6 degrees of freedom, namely the three translational degrees of freedom and the three rotational degrees of freedom. Of these, the translational degrees have been well explored in optical tweezers community. However, only the in-plane rotational degree of freedom has been explored. We call this in-plane degree of rotational freedom, the yaw motion in the nomenclature of the airlines. The pitch and roll degrees are only beginning to be explored recently.

In this talk, I will show you 4 ways of generating pitch rotation using the optical tweezers. I will also show you one way of detection of pitch rotation at high resolution using birefringent particles. Further, I will discuss some applications of this pitch rotation in soft matter systems and biology. I will also show you a few other projects that we are working on inside the lab.

Bio:
Basudev Roy got his MSc from Indian Institute of Technology Kharagpur and MS from the University of Maryland, College Park. He got his PhD from Indian Institute of Science Education and Research, Kolkata in 2015. He was an Alexander von Humboldt fellow at the University of Tuebingen, Germany for his postdoctoral research from 2015 to 2017. He joined Indian Institute of Technology Madras, India since 2017 where he is now an Associate Professor.

Presentation by H. Bachimanchi at Signals in the Sea mini-symposium, Lund University, 12 May 2023

Planktons imaged under a holographic microscope. (Illustration by J. Heuschele.)
Deep learning in plankton ecology
Harshith Bachimanchi
Presentation at Biology department, Lund University
12 May 2023, 13:00 CEST

In this mini-symposium organised by Dr. Erik Selander at Lund University, I have spoken about our recent work with marine microplankton, where we have combined holographic microscopy with deep learning to measure the ‘dry’ mass and 3D swimming dynamics of different species of planktons. The article related to this presentation can be found at the following here: Microplankton life histories revealed by holographic microscopy and deep learning.

The presentation was followed by discussions with Prof. Karin Rengefors group at Lund university on the topic of application of AI based methods for various kinds of studies in phytoplankton ecology and evolution.

Invited Seminar by G. Volpe at LOMA, Bordeaux, 2 May 2023

DeepTrack 2.1 Logo. (Image from DeepTrack 2.1 Project)
Deep Learning for Imaging and Microscopy
Giovanni Volpe
Seminar at LOMA, Bordeaux
2 May 2023, 14:00

Video microscopy has a long history of providing insights and breakthroughs for a broad range of disciplines, from physics to biology. Image analysis to extract quantitative information from video microscopy data has traditionally relied on algorithmic approaches, which are often difficult to implement, time consuming, and computationally expensive. Recently, alternative data-driven approaches using deep learning have greatly improved quantitative digital microscopy, potentially offering automatized, accurate, and fast image analysis. However, the combination of deep learning and video microscopy remains underutilized primarily due to the steep learning curve involved in developing custom deep-learning solutions. To overcome this issue, we have introduced a software, currently at version DeepTrack 2.1, to design, train and validate deep-learning solutions for digital microscopy.

Plenary Lecture by G. Volpe at SPIE Optics + Optoelectronics, Prague, 25 April 2023

DeepTrack 2.1 Logo. (Image from DeepTrack 2.1 Project)
AI and deep learning for microscopy
Giovanni Volpe
SPIE Optics + Optoelectronics, Prague, 25 April 2023
Time: 09:45

Video microscopy has a long history of providing insights and breakthroughs for a broad range of disciplines, from physics to biology. Image analysis to extract quantitative information from video microscopy data has traditionally relied on algorithmic approaches, which are often difficult to implement, time consuming, and computationally expensive. Recently, alternative data-driven approaches using deep learning have greatly improved quantitative digital microscopy, potentially offering automatized, accurate, and fast image analysis. However, the combination of deep learning and video microscopy remains underutilized primarily due to the steep learning curve involved in developing custom deep-learning solutions.

To overcome this issue, we have introduced a software, currently at version DeepTrack 2.1, to design, train and validate deep-learning solutions for digital microscopy. We use it to exemplify how deep learning can be employed for a broad range of applications, from particle localization, tracking and characterization to cell counting and classification. Thanks to its user-friendly graphical interface, DeepTrack 2.1 can be easily customized for user-specific applications, and, thanks to its open-source object-oriented programming, it can be easily expanded to add features and functionalities, potentially introducing deep-learning-enhanced video microscopy to a far wider audience.

Invited Talk by G. Volpe at 12th Nordic Workshop on Statistical Physics, Nordita, Stockholm, 15 March 2023

Logo of the AnDi challenge.
An Anomalous Competition: Assessment of methods for anomalous diffusion through a community effort
Giovanni Volpe
Nordita, Stockholm, 15 March 2023, 14:00

Deviations from the law of Brownian motion, typically referred to as anomalous diffusion, are ubiquitous in science and associated with non-equilibrium phenomena, flows of energy and information, and transport in living systems. In the last years, the booming of machine learning has boosted the development of new methods to detect and characterize anomalous diffusion from individual trajectories, going beyond classical calculations based on the mean squared displacement. We thus designed the AnDi challenge, an open community effort to objectively assess the performance of conventional and novel methods. We developed a python library for generating simulated datasets according to the most popular theoretical models of diffusion. We evaluated 16 methods over 3 different tasks and 3 different dimensions, involving anomalous exponent inference, model classification, and trajectory segmentation. Our analysis provides the first assessment of methods for anomalous diffusion in a variety of realistic conditions of trajectory length and noise. Furthermore, we compared the prediction provided by these methods for several experimental datasets. The results of this study further highlight the role that anomalous diffusion has in defining the biological function while revealing insight into the current state of the field and providing a benchmark for future developers.

Presentation by Lucas Le Nagard, 15 March 2023

Propulsion of a giant unilamellar vesicle containing E.coli cells. (From: doi:10.1073/pnas.2206096119)
Giant lipid vesicles propelled by encapsulated bacteria
Lucas Le Nagard
15 March 2023
11:00, PJ

I will present the results of a recent study of motile Escherichia coli bacteria encapsulated in lipid vesicles. For slightly deflated vesicles, swimming bacteria deform the vesicles and extrude membrane tubes reminiscent of those seen in eukaryotic cells infected by Listeria monocytogenes. These membrane tubes couple with the flagella of the enclosed bacteria to generate a propulsive force, turning the initially passive vesicles into swimmers. A simple theoretical model used to estimate the magnitude of the propulsive force demonstrates the efficiency of this physical coupling. Interestingly, such vesicle propulsion was not seen in recent studies of swimmers encapsulated in vesicles. While pointing to new design principles for conferring motility to artificial cells, our results illustrate how small differences often matter in active matter physics.

Invited Talk by G. Volpe at BIST Symposium on Microscopy, Nanoscopy and Imaging Sciences, Castelldefels, 10 March 2023

DeepTrack 2.1 Logo. (Image from DeepTrack 2.1 Project)
AI and deep learning for microscopy
Giovanni Volpe
BIST Symposium on Microscopy, Nanoscopy and Imaging Sciences
Castedefells, 10 March 2023

Video microscopy has a long history of providing insights and breakthroughs for a broad range of disciplines, from physics to biology. Image analysis to extract quantitative information from video microscopy data has traditionally relied on algorithmic approaches, which are often difficult to implement, time consuming, and computationally expensive. Recently, alternative data-driven approaches using deep learning have greatly improved quantitative digital microscopy, potentially offering automatized, accurate, and fast image analysis. However, the combination of deep learning and video microscopy remains underutilized primarily due to the steep learning curve involved in developing custom deep-learning solutions.

To overcome this issue, we have introduced a software, currently at version DeepTrack 2.1, to design, train and validate deep-learning solutions for digital microscopy. We use it to exemplify how deep learning can be employed for a broad range of applications, from particle localization, tracking and characterization to cell counting and classification. Thanks to its user-friendly graphical interface, DeepTrack 2.1 can be easily customized for user-specific applications, and, thanks to its open-source object-oriented programming, it can be easily expanded to add features and functionalities, potentially introducing deep-learning-enhanced video microscopy to a far wider audience.

Presentation by Sreekanth K Manikandan, 10 February 2023

Inferring entropy production in microscopic systems
Sreekanth K. Manikandan
Stanford University
10 February 2023, 15:00, Raven and Fox

An inherent feature of small systems in contact with thermal reservoirs, be it a pollen grain in water, or an active microbe flagellum, is fluctuations. Even with advanced microscopic techniques, distinguishing active, non-equilibrium processes defined by a constant dissipation of energy (entropy production) to the environment from passive, equilibrium processes is a very challenging task and a vastly developing field of research. In this talk, I will present a simple and effective way to infer entropy production in microscopic non-equilibrium systems, from short empirical trajectories [1]. I will also demonstrate how this scheme can be used to spatiotemporally resolve the active nature of cell flickering [2]. Our result is built upon the Thermodynamic Uncertainty Relation (TUR) which relates current fluctuations in non-equilibrium states to the entropy production rate.

References

[1] Inferring entropy production from short experiments [ Phys. Rev. Lett. 124, 120603 (2020) ]

[2] Estimate of entropy generation rate can spatiotemporally resolve the active nature of cell flickering [arXiv:2205.12849]

Bio: Sreekanth completed his PhD at the department of Physics, Stockholm University, in June 2020. His PhD supervisor was Supriya Krishnamurthy. From August 2020 – October 2022, Sreekanth was a Nordita fellow postdoc in the soft condensed matter group at Nordita. Currently, he is a postdoctoral scholar at the Department of Chemistry at Stanford University, funded by the Wallenberg foundation.

Presentation by Natsuko Rivera-Yoshida, 19 January 2023

M. xanthus cell-cell and cell-particle local interactions during cellular aggregation.
Transitions to multicellularity: the physical environment at the microscale
Natsuko Rivera-Yoshida
19 January 2023
16:30, Nexus

Physical environment contribute to both the robustness and the variation of developmental trajectories and, eventually, to the evolutionary transitions. But how? Myxococcus xanthus is a soil bacterium and is widely used as a biological model. In starvation conditions, cells move individually over the substrate into growing groups of cells which, eventually, organize into three-dimensional structures called fruiting bodies. Commonly, this developmental process is studied using standard experimental protocols that employ homogeneous and flat agar substrates, without considering ecologically relevant variables. However M. Xanthus has shown to drastically alter its development when modifying variables such as the substrate topography or stiffness. This modifications occur with trait and scale specificity, at the level of individual cells, large group of cells, fruiting bodies and also at the population scale. We use experimental and analytical tools to study how multicellular organization is altered at different spatial scales and developmental moments.

Presentation by Andreas Menzel, 19 January 2023

Individual and collective motion of nematic, polar, and chiral actively driven objects
Andreas Menzel
19 January 2023
15:30, Nexus

Abstract:
Actively driven objects comprise a manifold of possible different realizations: from self-propelling bacteria and artificial phoretically driven colloidal particles via vibrated hoppers to walking pedestrians. We analyze basic theoretical models to identify generic features of subclasses of such agents. Within this framework, we first address nematic objects [1]. They predominantly propel along one specific axis of their body, but do not feature an explicit head or tail. That is, they can move either way by spontaneous symmetry breaking. This leads to characteristic kinks along their trajectories. Second, we study chiral objects that show persistent bending of their trajectories and migrate in discrete steps [2]. When, additionally, they tend to migrate towards a fixed remote target, rich nonlinear dynamics emerges. It comprises period doubling and chaotic behavior as a function of the tendency of alignment, which is reflected by the trajectories. Third, we consider the collective motion of continuously moving chiral objects in crystal-like arrangements [3]. We here identify a localization transition with increasing chirality or self-shearing phenomena within the crystal-like structures. Overall, we hope by our work to stimulate experimental realization and observation of the various investigated systems and phenomena.

References
[1] A. M. Menzel, J. Chem. Phys. 157, 011102 (2022).
[2] A. M. Menzel, resubmitted.
[3] Z.-F. Huang, A. M. Menzel, H. Löwen, Phys. Rev. Lett. 125, 218002 (2020).

Short Bio:
Andreas Menzel studied physics at the University of Bayreuth (Germany), where he also completed his PhD on the continuum theory of soft elastic liquid-crystalline composite materials. After postdoctoral stays at the University of Illinois at Urbana-Champaign with Prof. Nigel Goldenfeld and at the Max Planck Institute for Polymer Research in Mainz in the department headed by Prof. Kurt Kremer, as well as research stays at Kyoto University with Prof. Takao Ohta, he completed his Habilitation at Heinrich Heine University Düsseldorf at the Theory Institute for Soft Matter headed by Prof. Hartmut Löwen. Amongst others, Andreas is interested in developing and applying explicit Green’s functions methods, statistical descriptions, and continuum theories on soft matter, addressing, for example, functionalized elastic composite materials and active matter. In 2020 he moved as a Heisenberg Fellow of the German Research Foundation to Otto von Guericke University Magdeburg (Germany), where he now heads the department on Theory of Soft Matter / Biophysics.