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Instabilities and Patterns in Active Systems: Effects of Substrate Friction, Geometry and Shape Fluctuations

Instabilities and Patterns in Active Systems: Effects of Substrate Friction, Geometry and Shape Fluctuations

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Instabilities and Patterns in Active Systems: Effects of Substrate Friction, Geometry and Shape Fluctuations
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<strong>Seminar of the School of Physical Sciences ----------------------------------------------</strong> Title: <strong>Instabilities and Patterns in Active Systems: Effects of Substrate Friction, Geometry and Shape Fluctuations</strong> Speaker: <strong>Pragya Srivastava</strong> (Syracuse University, Syracuse) Date: <strong>August 3, 2015</strong> <strong>Abstract:</strong> I will discuss the effects of substrate friction, geometry and shape changes on the dynamics and pattern formation in active systems with polar and apolar symmetries. I will present three different problems unified by a common theoretical approach based on the continuum modeling of active matter. First, motivated by the experiments on microtubule bundles confined to an oil-water interface, I will discuss the self-sustained dynamics of active nematic films. Upon eliminating the flow in the overdamped limit, one obtains closed equations for the nematic order parameter, with Frank constants renormalized by activity. Large values of activity can drive the renormalized elastic constants negative, Leading to instability of the uniformly ordered state. This minimal model yields emergent patterns of growing complexity with increasing activity. In second part of the talk I will shift the focus to polar active systems and will discuss the effects of substrate geometry in controlling the patterns of acto-myosin filaments in Fission Yeast cells and rod-shaped bacteria such as B. Subtillis. Using continuum models that couple orientation and curvature, I will show that the geometry of the cell is crucial in determining the steady state patterns of acto-myosin filaments. Moreover, the cellular shape not only influences the possible steady state patterns, but also determines their stability. These results are supported by experiments in spherical Fission Yeast cells demonstrating the important role played by cell shape in stabilizing the actor-myosin ring during cytokinesis. Finally, motivated by the observation of coupled fluctuations of acto-myosin density and membrane shape at the leading edges of moving and spreading cells, I will present a continuum model for the coupled dynamics of active cortical actin and the cell membrane.

A warm welcome to the modified and updated website of the Centre for East Asian Studies. The East Asian region has been at the forefront of several path-breaking changes since 1970s beginning with the redefining the development architecture with its State-led development model besides emerging as a major region in the global politics and a key hub of the sophisticated technologies. The Centre is one of the thirteen Centres of the School of International Studies, Jawaharlal Nehru University, New Delhi that provides a holistic understanding of the region.

Initially, established as a Centre for Chinese and Japanese Studies, it subsequently grew to include Korean Studies as well. At present there are eight faculty members in the Centre. Several distinguished faculty who have now retired include the late Prof. Gargi Dutt, Prof. P.A.N. Murthy, Prof. G.P. Deshpande, Dr. Nranarayan Das, Prof. R.R. Krishnan and Prof. K.V. Kesavan. Besides, Dr. Madhu Bhalla served at the Centre in Chinese Studies Programme during 1994-2006. In addition, Ms. Kamlesh Jain and Dr. M. M. Kunju served the Centre as the Documentation Officers in Chinese and Japanese Studies respectively.

The academic curriculum covers both modern and contemporary facets of East Asia as each scholar specializes in an area of his/her interest in the region. The integrated course involves two semesters of classes at the M. Phil programme and a dissertation for the M. Phil and a thesis for Ph. D programme respectively. The central objective is to impart an interdisciplinary knowledge and understanding of history, foreign policy, government and politics, society and culture and political economy of the respective areas. Students can explore new and emerging themes such as East Asian regionalism, the evolving East Asian Community, the rise of China, resurgence of Japan and the prospects for reunification of the Korean peninsula. Additionally, the Centre lays great emphasis on the building of language skills. The background of scholars includes mostly from the social science disciplines; History, Political Science, Economics, Sociology, International Relations and language.

Several students of the centre have been recipients of prestigious research fellowships awarded by Japan Foundation, Mombusho (Ministry of Education, Government of Japan), Saburo Okita Memorial Fellowship, Nippon Foundation, Korea Foundation, Nehru Memorial Fellowship, and Fellowship from the Chinese and Taiwanese Governments. Besides, students from Japan receive fellowship from the Indian Council of Cultural Relations.