Physics of Life
  Soft and Living Matter Group

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SOFT MATTER SEMINARS AND ZOOM LINKS.

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Dear All,

 

Please find the details of a physics seminar to be held on Tuesday, February 02, 2021, at 4:30 pm over Zoom.

 

Speaker: Prof. Frank Cichos

               Leipzig University, Germany

 

Title:  Moving Molecules and Particles with Heat
 

Abstract: 

The local generation of heat by optical pumped metal nanostructures allows to create well-defined temperature fields that offer new possibilities to manipulate molecules and particles in liquids. At the same time the thermal non-equilibrium poses new fundamental physical questions.In this lecture, I will introduce various temperature-induced effects that can be employed to trap molecules without external forces or to create active matter that will respond to light. I will show how these effects in conjunction with a sophisticated feedback control can help to explore, for example, protein aggregation or the collective behavior of active particles. 

 

IISER-PHY PUNE is inviting you to a scheduled Zoom meeting.

 

Topic: Soft + Living matter seminar - Prof. Frank Cichos

Time: Feb 2, 2021 04:30 PM India

 

Join Zoom Meeting

https://zoom.us/j/97536198701?pwd=WWV2MWpYemlnUDhJaHU4S0NOUjhPUT09

 

Meeting ID: 975 3619 8701

Passcode: 539776

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Dear All,

 

Please find the details of a physics seminar to be held on Friday, January  29, 2021, at 9:00 pm over Zoom.

Please note, the seminar time is changed to 9:00 pm (instead of 9 am).

 

Speaker:  Prof.  Oleg D. Lavrentovich
                Advanced Materials and Liquid Crystal Institute,

                Department of Physics and Chemical Physics Interdisciplinary Program,

                Kent State University, Kent, Ohio 44242, USA

 

Title: Dynamics of micro-organisms controlled by liquid crystals


Abstract: 

 

 

Active systems such as swarms of swimming bacteria and cell tissues demonstrate fascinating dynamics that can potentially be used in microscale applications. Control of this dynamics in isotropic media such as water is difficult.  We describe an approach in which instead of an isotropic medium, the dynamics of micro-organisms is guided by a liquid crystal.  An example with a droplet of an active bacterial suspension shows an immediate benefit of such a replacement: when placed in an isotropic fluid, the droplet experiences random Brownian motion, but once the medium becomes a nematic liquid crystal, the droplet acquires an ability to swim unidirectionally along a prescribed trajectory [1]. Other examples of liquid crystal control over the dynamics of microscopic objects include dynamic swarms of swimming bacteria [2-4] and living tissues [5]. Director gradients and topological defects impact the biological microstructures most strongly, causing spatial variation of bacterial concentration and cell phenotype and shaping irreversible active flows.  The physical mechanisms are shaped by the nontrivial effect of the orientational order of a liquid crystal on the interactions of dynamic active units.  The control of active matter by patterned liquid crystals might result in new approaches to harness the energy of collective motion for micro-robotic, biomechanical, biomedical, and sensing applications. The work is supported by NSF DMR-1905053, CMMI-1663394, and DOE DE-SC0019105 grants.

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[1]            M. Rajabi, B. Hend, T. Turiv, and O. D. Lavrentovich, Directional self-locomotion of active droplets enabled by nematic environment, Nature Physics, https://doi.org/10.1038/s41567-41020-01055-41565 (2020).

[2]            C. Peng, T. Turiv, Y. Guo, Q.-H. Wei, and O. D. Lavrentovich, Command of active matter by topological defects and patterns, Science 354, 882-885 (2016).

[3]            T. Turiv, R. Koizumi, K. Thijssen, M. M. Genkin, H. Yu, C. Peng, Q.-H. Wei, J. M. Yeomans, I. A. Aranson, A. Doostmohammadi, and O. D. Lavrentovich, Polar jets of swimming bacteria condensed by a patterned liquid crystal, Nature Physics 16, 481–487 (2020).

[4]            R. Koizumi, T. Turiv, M. M. Genkin, R. J. Lastowski, H. Yu, I. Chaganava, Q.-H. Wei, I. S. Aranson, and O. D. Lavrentovich, Control of bacterial swirls by spiral nematic vortices: Transition from individual to collective motion and contraction, expansion, and stable circulation of bacterial swirls, Physical Review Research 2, 033060 (2020).

[5]            T. Turiv, J. Krieger, G. Babakhanova, H. Yu, S. V. Shiyanovskii, Q. Wei, -H., M.-H. Kim, and O. D. Lavrentovich, Topology control of human fibroblast cells monolayer by liquid crystal elastomer, Science Advances 6, eaaz6485 (2020).

 

 

Topic: Seminar - Oleg D. Lavrentovich
Time: Jan 29, 2021 09:00 PM Mumbai, Kolkata, New Delhi

Join Zoom Meeting
https://zoom.us/j/98049215438?pwd=YTQ5Y3crRDZKQUpYMXBudXVkak5uQT09

Meeting ID: 980 4921 5438
Passcode: 093029

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Speaker: Prof. Giovanni Volpe
Gothenburg University, Sweden

Title: Deep learning for microscopy and optical trapping

Time: Jan 21, 2021 04:30 PM India

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https://zoom.us/j/91448769854?pwd=K1Y3MEtBTkFIN1FNdDF6R3VQTlRmZz09

Meeting ID: 914 4876 9854

Passcode: 438858

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Abstract:
After a brief overview of artificial intelligence, machine learning and deep learning, I will present a series of recent works in which we have employed deep learning for applications in photonics and active matter. In particular, I will explain how we employed deep learning to enhance digital video microscopy, to estimate the properties of anomalous diffusion, to characterize microscopic force fields, to improve the calculation of optical forces, and to characterize nanoparticles. Finally, I will provide an outlook for the application of deep learning in photonics and active matter.


IISER-PHY PUNE is inviting you to a scheduled Zoom meeting.

Topic: Soft + Living Matter Seminar - Giovanni Volpe
 

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Speaker:  Dr. Roberto Cerbino

                University of Milan

                web: http://www.cerbino.eu

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Join Zoom Meeting

https://zoom.us/j/99186660296?pwd=c0tTOXdNWGlKQjFZOEx6Q1BaeTI4Zz09

 

Meeting ID: 991 8666 0296

Passcode: 476317

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Title:   Probing multi-scale activity in complex fluids and biological systems with differential dynamic microscopy

Abstract: 

Differential dynamic microscopy (DDM) is a technique that exploits optical microscopy to obtain local, multi-scale quantitative information about dynamic samples, in most cases without user intervention. It is proving extremely useful in understanding dynamics in liquid suspensions, soft materials, cells, and tissues. In DDM, image sequences are analyzed via a combination of image differences and spatial Fourier transforms to obtain information equivalent to that obtained by means of light scattering techniques. For many questions, DDM has advantages compared to scattering techniques, as well as to segmentation/tracking and correlation techniques like particle image velocimetry. The very straightforward DDM approach, originally demonstrated with bright field microscopy of aqueous colloids [1], has lately been used to probe a variety of other complex fluids and biological systems with many imaging methods, including dark-field, differential interference contrast, wide-field, light-sheet, and confocal microscopy [2]. The number of adopting groups is rapidly increasing and so are the applications. Here, we briefly recall the working principles of DDM, we highlight its advantages and limitations, we outline recent experimental breakthroughs, and we provide a perspective on future challenges and directions [3].

References
[1] R. Cerbino, V. Trappe, Phys. Rev. Lett. 100 2008, 188102
[2] F. Giavazzi, R. Cerbino, J. Opt. 16 2014, 083001
[3] R. Cerbino, P. Cicuta, J. Chem. Phys. 147 2017, 110901

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IISER-PHY PUNE is inviting you to a scheduled Zoom meeting.

 

Topic: Soft + Living Matter Seminar - Dr. Roberto Cerbino

Time: Jan 19, 2021 04:30 PM India

 

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on Tuesday, January 12, 2020, at 4:30 pm over Zoom.

 

Speaker:   Prof. Clemens Bechinger

                 University of Konstanz, Germany

 

 

Title:   Critical dynamics in collective states of active particles

 

Abstract: 

Functional collective states in living systems are thought to exhibit an optimal balance between stability and sensitivity to external perturbations. One way to achieve such behavior is that individuals adjust their response to neighbors so that the entire group operates near a critical point that separates distinct dynamical collective states. Since responses between individuals in living systems cannot easily be changed, evidence for critical behavior in groups of birds, insects, and also micron-sized protozoa, has mainly been inferred from how their properties vary as a function of group size or density. Here we demonstrate critical collective behavior in a system of active colloidal particles (APs), achieved through variations of their mutual interactions using feedback control. At the transition between a swarm and a swirl we observe an explicit bifurcation dynamics of the rotational order parameter and a critical slowing down, i.e., a growth of the relaxation time by almost one order of magnitude. Additional signatures of critical dynamics, including hysteresis in presence of symmetry-breaking particle interactions, and a maximum of the susceptibility, are measured and characterized in terms of a theoretical model which is based purely on the time-reversal symmetry of the order parameter. Our results suggest that collective dynamics can be tuned not only via group size but also by small behavioral changes between group members.

 

 

1.        T. Bäuerle, R. C. Löffler, C. Bechinger, Formation of stable and responsive collective states in suspensions of active colloids. Nature Comm. 11, 1-9 (2020).

2.        F. Lavergne, H. Wendehenne, T. Bäuerle, C. Bechinger, Group formation and cohesion of active particles with visual perception-dependent motility. Science 364, 70-74 (2019).

 

 

IISER-PHY PUNE is inviting you to a scheduled Zoom meeting.

 

Topic: Soft + Living Matter Seminar - Clemens Bechinger

Time: Jan 12, 2021 04:30 PM India

 

Join Zoom Meeting

https://zoom.us/j/96598123175?pwd=eDc5UFcyZ3NZajBLa2xiWWR0VVVHZz09

 

Meeting ID: 965 9812 3175

Passcode: 668545

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Speaker:     L. Isa

                   ETH Zurich, Switzerland

 

 

Title:    Active Colloids with External and Internal Feedback 

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Time: Jan 5, 2021 02:30 PM India

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Join Zoom Meeting

https://zoom.us/j/97222108031?pwd=ZENGVm1jQVF3RG9aTHJjSDdVRWF0Zz09

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Meeting ID: 972 2210 8031

Passcode: 004207

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Abstract: 

As research on artificial microswimmers continues to fascinate a broad community of scientists, new directions emerge by extending the scope of their application and by introducing new ways to control active motion. In this talk, I will first describe the case of active magnetic particles with external feedback. By applying randomly oriented magnetic fields, we can effectively impose rotational diffusivities decoupled from the bath temperature. This, combined with real-time tracking of the particle position, makes it possible to realize landscapes of spatially varying rotational diffusion with dramatic consequences on particle dynamics. By comparing experiments with numerical simulations, we show that interesting anomalous diffusion and particle localization emerge [1].

I will then present the case of reconfigurable active colloids that display a coupling between motility, internal properties (such as shape and dielectric properties) and environmental stimuli. I will illustrate the way in which we fabricate these particles, comprising soft responsive microgels, and discuss the detailed mechanisms of the dynamical coupling [2].  Both parts indicate new ways in which we can control the active motion of artificial microswimmers, taking us one step closer to realizing the vision of autonomous active materials.

 

 

References

[1  [1] MA Fernandez-Rodriguez, F Grillo, L Alvarez, M Rathlef, I Buttinoni, G Volpe and L Isa

     “Feedback-controlled active Brownian colloids with space-dependent rotational dynamics”, Nature Communications 11: 4223 (2020)

      [2]  L Alvarez, MA Fernandez-Rodriguez, A Alegria, S Arrese-Igor, K Zhao, M Kröger and L Isa, "Reconfigurable Active Colloids with Internal Feedback"
       submitted, https://arxiv.org/abs/2009.0838

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Speaker:    Juliane Simmchen
                  Technical University of Dresden, Germany

                   https://simmchenresearch.wordpress.com/about/

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 Title:    Photocatalytic motion on the microscale

 

Join Zoom Meeting

https://zoom.us/j/97108325080?pwd=TVVjc1NuakpSc0ZhOTREa0xYQkdiZz09

 

Meeting ID: 971 0832 5080

Passcode: 144497

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Abstract: 

Synthetic active matter has become a core interest in physics due to its ability to emulate living systems. Many living systems are able to gain their energy from sunlight by performing photosynthesis, a complex process which is currently not in reach of synthetic systems. However, there are a few alternative reactions that can be used to propel active matter. Using chemically active Janus particles, we explored that the presence of actively moving colloids induces self-assembly processes of passive particles in their surroundings.[1] The motion of chemically active colloids is conditioned by a chemical field as well as a hydrodynamic flow field which determine both, the motility as well as the influence on their surroundings. This effect becomes more pronounced and controllable, when semiconducting particles are used. [2][3] To understand the origin of these behaviors, we consider the individual contributions and analyze the swimming behaviors under different circumstances.[4]

 

References:

[1] J Simmchen, J Katuri, WE Uspal, MN Popescu, M Tasinkevych, Topographical pathways guide chemical microswimmers, Nature Communications, 7, 10598 (2016).

[2] LL Wang, A Kaeppler A, D Fischer, J Simmchen, Photocatalytic TiO2 micromotors for removal of microplastics and suspended matter, ACS AMI, 11, 3632937-32944 (2019).

[3] S Heckel, J Simmchen, Photocatalytic BiVO4 Micro Swimmers with Bimodal Swimming Strategies, Adv. Intelligent Systems, 2019, 201900093.

[4] S Heckel, J Grauer, M Semmler, T Gemming, H Löwen, B Liebchen, J Simmchen Active Assembly of Spheroidal Photocatalytic BiVO4 Microswimmer, Langmuir (2020).

 

IISER-PHY PUNE is inviting you to a scheduled Zoom meeting.

 

Topic: Soft + Living Matter Seminars - Juliane Simmchen

Time: Dec 23, 2020 04:30 PM India

 

Join Zoom Meeting

https://zoom.us/j/97108325080?pwd=TVVjc1NuakpSc0ZhOTREa0xYQkdiZz09

 

Meeting ID: 971 0832 5080

Passcode: 144497