Dibyendu Das

Associate Professor

Contact Information

Address : Physics Department, IIT Bombay, Powai, Mumbai 400076, India.
E-mail: dibyendu@phy.iitb.ac.in
Telephone : 25767555 (Office), 25768555 (Residence)
Fax : 25767552

Academic Qualifications

I.S.C. (10+2, St. Pauls Mission School, Calcutta, in 1990)
B.Sc. (Presidency College, University of Calcutta, in 1993)
M.Sc. (IIT Kanpur, in 1995)
Ph.d. (Tata Institute of Fundamental Research, Mumbai, India, in 2000)
Post-doctoral fellow (Brandeis University, USA, 2000-2002)
Post-doctoral fellow (Laboratoire LPTMS, Universite Paris Sud, Orsay, France, 2002-2003)
Faculty (IIT Bombay, India, 2003 - now)

Research Interests

We have the following broad directions of research:

(I) Stochastic processes in biological systems.
(II) Stochastic processes in physical systems.
(III) Dynamics of dilute granular systems without drive.
(IV) Dynamics of driven active systems.

*Stochastic processes in biological systems*

A) Dynamics of cytoskeletal filaments:
Actin and microtubules are dynamic cytoskeletal filaments within cells which grow and shrink and generate requisite amount of forces which are utilised by the cells for various purposes. We study the basic mechanisms of their dynamics and force generation through simple modelling. Recently we have discovered some interesting facts about their collective behaviour –
(i) “Collective force generated by multiple biofilaments can exceed the sum of forces due to individual ones”, New J. Phys. 16, 063032 (2014).

B) Kinetics of nucleosome binding and unbinding to DNA:
DNA is wrapped around structures called nucleosomes, but have to often unwrap to allow for important functions like “transcription” to happen. Nucleosome kinetics and DNA exposure is an important problem on which we are working.

C) Stochastic fluctuations in microbial populations:
It is well-known from the old works of Luria and Delbruck that growth phases of microbial populations undergoing birth and spontaneous mutations exhibit “giant fluctuations” violating central limit theorem. Recently we have shown that such large fluctuations are relevant even in microbial populations having more complex processes –
(i) “Giant number fluctuations in microbial ecologies”, Jr. Theo. Bio. 308, 96 (2012).

D) Collective motion of cells:
Experiments on collectively moving cells exhibit large scale velocity ordering, pattern formation, and large traction force fluctuations in wound healing assays. Our simple modelling captures some of these aspects —
(i) ``Broad-tailed force distributions and velocity ordering in a heterogeneous membrane model for collective cell migration’‘, Europhys. Lett. 99, 18004 (2012).

*Stochastic processes in physical systems*

In recent years, flourescent microscopic studies of single polymers in various laminar flows have revealed very accurate measures of static and dynamic properties of polymers. Flow patterns can be elongational, rotational, shear, or random. In particular, in shear flow, the polymer exhibits an interesting tumbling motion. We have studied the latter phenomenon recently for a flexible polymer (see (i) and (ii)). Other first passage problems related to polymer motion have been studied in (iii) and (iv) below.
(i) “Dynamics of a flexible polymer in planar mixed flow”,
J. Phys.: conf. ser. 297, 012007 (2011).
(ii) “Accurate statistics of a flexible polymer chain in shear flow”
Phys. Rev. Lett. 101, 188301 (2008).
(iii) “Persistence of a Rouse polymer chain under transverse shear flow”,
Phys. Rev. E 75, 061122 (2007).
(iv) “Persistence of Randomly Coupled Fluctuating Interfaces”,
Phys. Rev. E 71, 036129 (2005).

*Dynamics of dilute granular systems without drive*

Granular systems (like sand or marbles) can be forced to flow (by shaking, or applying shear), but without drive they freely dissipate energy and “cool”. We have a long-term project on understanding this system using Molecular-Dynamics simulations of inelastic particles and scaling theories, in their highly correlated and inhomogeneous cooling regime. The most challenging problem is to find out the universal characteristics of the system, and develop correct coarse-grained descriptions. We have studied the system in 1-dimension (papers (iii)-(vi) below), and recently in 2-dimensions (paper (i)), and in 3-dimensions (paper (ii) below).

(i) “Inhomogeneous cooling of the rough granular gas in two dimensions”,
Europhys. Lett. 107, 44001 (2014).
(ii) “Energy decay in Three-dimensional freely cooling granular gas”,
Phys. Rev. Lett. 112, 038001 (2014).
(iii) “Coarse grained dynamics of the freely cooling granular gas in one dimension”,
Phys. Rev. E 84, 031310 (2011).
(iv) “Lattice models for ballistic aggregation in one dimension”,
Europhys. Lett. 93, 44001 (2011).
(v) “Equivalence of the freely cooling granular gas and the sticky gas”,
Phys. Rev. E 79, 021303 (2009).
(vi) “Violation of Porod law in a freely cooling granular gas in one dimension”,
Phys. Rev. Lett. 99, 234505 (2007).

*Dynamics of driven active systems*

Study of spatio-temporal pattern formation in flocks of animals (birds, fishes, insects, bacteria), in motile actin and microtubule assays, and in driven granular disks and rods have been an active area of research over the past decade. Theoretically these systems are studied using rule based models of discrete objects, as well as coarse-grained continuum approaches. One of our recent work on this subject is –
(i) “Spatial structures and Giant number fluctuations in models of active Matter”,
Phys. Rev. Lett. 108, 238001 (2012).

Awards

American Physical Society (APS-IUSSTF) Professorship award (2011) – delivered a lecture series at Colorado State University.

Satyamurthy award, from Indian Physics Association (2009).

Excellence in teaching award, from IIT Bombay (2008).

Courses taught

1. Spring ‘10, ‘11, ‘12, ‘13: Statistical Mechanics (PH 304).
2. Autumn ‘07, ‘08, ‘14: Advanced Statistical Mechanics (EP 403).
3. Spring ‘07, ‘08, ‘09, ‘14: Mathematical Methods II – Complex analysis and ODEs (PH 408).
4. Autumn ‘04, ‘05, ‘06, ‘09, ‘10, ‘11, ‘12: Classical Mechanics (PH 401, EP 222).
5. Spring ‘04, ‘05, ‘06: Electricity and Magnetism (PH 102).

Ph.d. Students

1. Mahendra Shinde
Thesis: Spatio-temporal pattern formation in freely cooling granular gases (submitted – 2009; defended – June 2010).
Currently: Post-doctoral fellow (in JNCASR)

2. Supravat Dey
Thesis: Pattern formation in Active matter and Dissipative systems. (submitted – July 2012; defended – October 2012)
Currently: Post-doctoral fellow (in Rome, Italy)

3. Dipjyoti Das
Thesis: Stochastic processes in cytoskeletal filaments and microbial populations (submitted July 2014)
Currently: RA at IITB

4. Aparna J.S.
(In collaboration with Prof. Ranjith P. of Bio-Sc and Bio-Engg, IITBombay)
Thesis: Dynamics of bio-filaments.
Currently: 2nd year

Projects

1. Sponsored project (completed): Indo-French Center – IFCPAR/CEFIPRA (project no. 3404-2).
Period: 01.05.2006 – 30.04.2009.
Jointly with J.L. Jacobsen, Alain Comtet and S.N. Majumdar (of Laboratoire LPTMS., Orsay,France) and Deepak Dhar and Mustansir Barma (of TIFR Mumbai).

Publications

31. “Inhomogeneous cooling of the rough granular gas in two dimensions”,
Sudhir N. Pathak, Dibyendu Das and R. Rajesh,
Europhys. Lett. 107, 44001 (2014).

30. “Collective force generated by multiple biofilaments can exceed the sum of forces due to individual ones”,
Dipjyoti Das, Dibyendu Das and Ranjith Padinhateeri,
New J. Phys. 16, 063032 (2014).

29. “Energy decay in Three-dimensional freely cooling granular gas”,
Sudhir N. Pathak, Zahera Jabeen, Dibyendu Das and R. Rajesh,
Phys. Rev. Lett. 112, 038001 (2014).

28. “Broad-tailed force distributions and velocity ordering in a heterogeneous membrane model for collective cell migration”,
Tripti Bameta, Dipjyoti Das, Sumantra Sarkar, Dibyendu Das, and Mandar Inamdar,
Europhys. Lett. 99, 18004 (2012).

27. “Giant number fluctuations in microbial ecologies”,
Dipjyoti Das, Dibyendu Das, and Ashok Prasad,
Jr. Theo. Bio. 308, 96 (2012).

26. “Spatial structures and Giant number fluctuations in models of active Matter”,
Supravat Dey, Dibyendu Das, and R. Rajesh,
Phys. Rev. Lett. 108, 238001 (2012).

25. “Coarse grained dynamics of the freely cooling granular gas in one dimension”,
Mahendra Shinde, Dibyendu Das, and R. Rajesh,
Phys. Rev. E 84, 031310 (2011).

24. “Dynamics of a flexible polymer in planar mixed flow”,
Dipjyoti Das, Sanjib Sabhapandit, and Dibyendu Das,
J. Phys.: conf. ser. 297, 012007 (2011).

23. “Lattice models for ballistic aggregation in one dimension”,
Supravat Dey, Dibyendu Das, and R. Rajesh,
Europhys. Lett. 93, 44001 (2011).

22. “Intrinsic noise induced resonance in presence of sub-threshold signal in Brusselator”,
Supravat Dey, Dibyendu Das, and P. Parmananda,
Chaos 21, 033124 (2011).

21. “Predicting the coherence resonance curve using a semianalytical treatment”,
Santidan Biswas, Dibyendu Das, P. Parmananda, and Anirban Sain,
Phys. Rev. E 80, 046220 (2009).

20. “Equivalence of the freely cooling granular gas to the sticky gas”,
Mahendra Shinde, Dibyendu Das, and R. Rajesh,
Phys. Rev. E 79, 021303 (2009).

19. “Accurate statistics of a flexible polymer chain in shear flow”,
Dibyendu Das and Sanjib Sabhapandit,
Phys. Rev. Lett. 101, 188301 (2008).

18. “Critical behavior of loops and biconnected clusters on fractals of dimension d < 2”,
Dibyendu Das , Supravat Dey, Jesper Lykke Jacobsen, and Deepak Dhar,
J. Phys. A: Math. Theor. 41, 485001 (2008).

17. “Violation of Porod law in a freely cooling granular gas in one dimension”,
Mahendra Shinde, Dibyendu Das, and R. Rajesh,
Phys. Rev. Lett. 99, 234505 (2007).

16. “Persistence of a Rouse polymer chain under transverse shear flow”,
Somnath Bhattacharya, Dibyendu Das, and Satya N. Majumdar,
Phys. Rev. E 75, 061122 (2007).

15. “Motion of a random walker in a quenched power law correlated velocity field”,
Soumen Roy and Dibyendu Das,
Phys. Rev. E 73, 026106 (2006).

14. “Critical Dynamics of Dimers: Implications for the Glass Transition”,
Dibyendu Das, Greg Farrell, Jane’ Kondev and Bulbul Chakraborty,
J. Phys. Chem. B 109, 21413 (2005).

13. “Persistence of Randomly Coupled Fluctuating Interfaces”,
Satya N. Majumdar and Dibyendu Das,
Phys. Rev. E 71, 036129 (2005).

12. “Landau-like theory of glassy dynamics”,
Satya N. Majumdar, Dibyendu Das, Jane’ Kondev, and Bulbul Chakraborty,
Phys. Rev. E 70, 060501 (Rapid communications) (2004).

11. “Two-dimensional O(n) model in a staggered field”,
Dibyendu Das and Jesper Lykke Jacobsen,
J. Phys. A: Math. Gen. 37, 1-35 (2004).

10. “Activated dynamics at a non-disordered critical point”,
Dibyendu Das, Jane’ Kondev and Bulbul Chakraborty,
Europhys. Lett. 61 (4), 506 (2003).

9. “Topological jamming and the glass transition in a frustrated system”,
Bulbul Chakraborty, Dibyendu Das, and Jane’ Kondev,
Eur. Phys. J. E 9, 227 (2002).

8. “Jamming in a model glass: Interplay of dynamics and thermodynamics”,
Bulbul Chakraborty, Dibyendu Das, and Jane’ Kondev,
Physica A 318, 23 (2003).

7. “Aggregate formation in a system of coagulating and fragmenting particles with mass-dependent diffusion rates”,
R. Rajesh, Dibyendu Das, Bulbul Chakraborty, and Mustansir Barma,
Phys. Rev. E 66, 056104 (2002).

6. “Phase diagram of a two-species lattice model with a linear instability”,
Sriram Ramaswamy, Mustansir Barma, Dibyendu Das and Abhik Basu,
Phase Transitions 75 (Nos. 4 & 5), 363 (2002).

5. “Fluctuation dominated phase ordering driven by stochastically evolving surfaces: depth models and sliding particles”,
Dibyendu Das, Mustansir Barma and Satya N. Majumdar,
Phys. Rev. E 64, 046126 (2001).

4. “Weak and strong dynamic scaling in a one-dimensional driven coupled-field model: effects of kinematic waves”,
Dibyendu Das, Abhik Basu, Mustansir Barma and Sriram Ramaswamy,
Phys. Rev. E 64, 021402 (2001).

3. “Particles sliding on a fluctuating surface: phase separation and power laws”,
Dibyendu Das and Mustansir Barma,
Phys. Rev. Lett. 85, 1602 (2000).

2. “Arrested states formed on quenching spin chains with competing interactions and conserved dynamics”,
Dibyendu Das and Mustansir Barma,
Phys. Rev. E 60, 2577 (1999).

1. “Polytype kinetics and quenching of spin chains with competing interactions using trimer-flip dynamics”,
Dibyendu Das and Mustansir Barma,
Physica A 270, 245 (1999).


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