Welcome
to my homepage!

I am currently a
postdoc/visiting scientist at the Courant Institute, New York
University,

working with Mike Shelley
and Jun
Zhang, in the Applied Math Lab (AML).

I am studying
biomechanics of locomotion,
specifically locomotion of C elegans in structured environments.

(A comprehensive database about various aspects of C elegans biology is at Wormbase)

My earlier reasearch as a postdoc at MIT in Gareth McKinley's Lab was in

non-Newtonian fluid dynamics, specifically viscoelastic jets.

(A very instructive set of videos about Newtonian, and non-Newtonian fluid dynamics is available here.)

(A good resource for rheology is the Society of Rheology, SOR.)

Prior
to
this, I was a graduate student at Duke University, Department of Physics,

working with Professor
Bob Behringer
on granular systems.

**Research:**

**1.
Bio-fluid Dynamics and Bio-Mechanics: Locomotion of C. elegans in structured
environments**

**
**

The focus of my current research is to understand low Reynolds number locomotion

of microorganisms. Undulatory locomotion of microorganisms in complex environments is

ubiquitous in nature. For example, a sperm moving through mucus, or a Spirochaete moving

through tissue. Microorganisms navigate complex environments consisting of fluids and

obstacles, negotiating hydrodynamic effects and geometrical constraints.

Some of the key questions are:

What role do hydrodynamics and geometrical constraints play? Do these obstacles help or hinder

their motion?

To gain insights into these questions, I am studying undulating locomotion of C. elegans in

PDMS micro-pillar arrays filled with buffer solution. Such a setup allows systematic control over

geometric constraints, and along with hydrodynamic simulations, determines the role of

hydrodynamic contributions.

We have found that the nematode (L ~ 1 mm), while swimming between the pillars, employs a number

of different locomotory strategies depending on the lattice spacing (q: [0.380 - 0.700] mm).

Instead of being hindered by the obstacles, it can utilize them to push off and gain speed.

These regimes of enhanced locomotion depend on the lattice spacing scaled by the length of

the nematode. In addition, we also observe changes in frequency, velocity, curvature, and the gait

of the worm as a function of the scaled lattice spacing. Our experimental approach, in conjunction with

modeling and simulations (Eric Keaveny and Mike Shelley), allow us to disentangle the effects of

geometry and hydrodynamics on end behavior. We find that the simulations not only reproduce

locomotory strategies of the real nematode, but also match the experimental measurements of enhanced

velocity quantitatively. Combining experiments and simulations, we can now establish a regime map of

changes in locomotory strategies of an undulating swimmer in structured media

Paper (Accepted for Publication, Royal Soc. J. of Interface):

Experiments and Theory of Undulatory Locomotion in a Simple Structured Medium

Supplementary Material: The Mechanical Worm Model

Supplementary Movies: (combined Zip File: Supplementary Movies )

1) Movie 1 (Experimental Movie)

2) Movie 2 (Experimental Movie)

3) Movie 3 (Experimental Movie)

4) Movie 4 (Simulations Movie)

5) Movie 5 (Simulations Movie)

6) Movie 6 (Simulations Movie)

7) Movie 7 (Simulations Movie)

Here is the movie
for
DFD Gallery of
Fluid Motion: Locomotion
of C. elegans in Structured Media

Extra
Movie
files:

1) Demo-1-Large-Lattice-Movie

2) Demo-2-Small-Lattice-Movie

**2.
Granular Physics: (Advisor: Bob Behringer, Duke University, Physics)**

**
**

The focus of my graduate research was on understanding the statistical properties of dense, dry

granular systems under isotropic compression and pure shear. The key feature of granular

systems is the heterogeneous network of contact forces called the “force-chain” network.

Understanding these force networks and their spatial correlations is a fundamental goal of

granular mechanics. Although knowledge of inter-grain contact forces is indispensable

for a complete understanding of the system, they are exceedingly difficult to measure

non-destructively in a realistic granular system. I developed a novel method to measure

both the normal and tangential components of contact forces, in bulk samples, at the grain scale [1].

We visualized the stresses by using birefringent circular disks and solved the inverse problem

of finding the contact forces producing the observed stress patterns. Figure shows an experimental

image (left) of sheared granular system, and the corresponding "best-fit" image obtained after finding

the contact forces.

**3.
Non-Newtonian Fluid Dynamics: Jetting of Viscoelastic Fluids (Advisor:
Gareth McKinley, Mech. E. MIT)**

Viscoelastic jets with moderate elasticities exhibit a rich array of complex nonlinear dynamics:

the buckling instability of a steady jet resulting in periodic coiling, and a transition from periodic

to quasi-periodic dynamics, followed by a transition to multi-frequency, chaotic dynamics. Beyond

this regime, the jet dynamics smoothly crosses over to exhibit a spectacular ``leaping shampoo" or the

Kaye effect. We created a regime map of the dynamics of the jet in terms of viscous, elastic,

gravitational, and inertial effects, allowing us to connect rheology of the fluids to the changes in the

dynamics of the jets. We examined different dynamical regimes in terms of scaling variables, which

depend on the geometry (dimensionless height), kinematics (dimensionless flow rate), and the fluid

properties (elasto-gravity number). This approach allowed us to unify diverse phenomena like dripping,

coiling, and leaping jets, as a sequence of transitions in the parameter space of scaled flow rate and scaled

height.

Fluids with higher elasticities predominantly tend to exhibit folding motions (linear oscillations)

instead of circular coiling. There is also an absence of any ``leaping shampoo" effect, and at larger

heights, the jet ruptures as it cannot sustain the elastic stresses. The regime map of the dynamics for

high elasticity fluids was also established along the same lines.

1.
T. S. Majmudar and R. P. Behringer, "Contact force
measurements and stress induced anisotropy

in granular materials", Nature 435, 1079-1082, (2005).

PDF of the Paper

2. T. S. Majmudar, and R. P. Behringer, "Contact forces and stress induced anisotropy",

Powders and Grains 2005, 65-68, (2005) (Cover Image).

3. T. S. Majmudar, M. Sperl, S. Luding and R. P. Behringer “Jamming transition

in granular systems”, Physical Review Letters, 98, 058001 (2007) (Cover Article).

PDF of the Paper

4. C. J. Pipe, T. S. Majmudar, and G. H. McKinley “High Shear Rate Viscometry”,

Rheologica Acta, 47, 5, 621-642, (2008).

PDF of the Paper

5. R.P. Behringer, K.E. Daniels, T. S. Majmudar, and M. Sperl, Fluctuations, Correlations, and

Transitions in Granular Materials: Statistical Mechanics for a Non-Conventional System,

Phil. Trans. Roy. Soc. A – Math. Phy. and Eng. Sci., 366, 1865, 493-504, (2008).

PDF of the Paper

6. Jie Zhang, Trush Majmudar, and R.P. Behringer, “Force chains in a two-dimensional granular

pure shear experiment”, Chaos, 18, 041107-1, (2008).

PDF of the Paper

7. G. Lois, J. Zhang, T. S. Majmudar, S. Henkes, B. Chakraborty, C. S. O’Hern, R. P. Behringer,

“Stress correlations in granular materials: an entropic formulation”, Physical Review E , 80,

060303(R), (2009).

PDF of the Paper

8. J. Zhang, J. Ren, S. Farhadi, R. P. Behringer, T. S. Majmudar and A. Tordesillas, “Dense 2D

Granular Material Subject to Cyclic Pure Shear”, Powders and Grains 2009, 553—556,

(2009).

9. J. Zhang, R. P. Behringer, T. S. Majmudar and M. Sperl, “Experiments on Force Fluctuations

and the Jamming Transition”, Powders and Grains 2009, 527—530, (2009).

10. J. Zhang, T .S. Majmudar, A. Tordesillas, and R.P. Behringer, “Statistical properties of a 2D

granular material subjected to cyclic shear”, Granular Matter, 12, 159, (2010).

PDF of the Paper

11. J. Zhang, T. S. Majmudar, M. Sperl, and R. P. Behringer, “Jamming for a 2D granular

material”, Soft Matter, 6, 2982-2991, (2010).

PDF of the Paper

in granular materials", Nature 435, 1079-1082, (2005).

PDF of the Paper

2. T. S. Majmudar, and R. P. Behringer, "Contact forces and stress induced anisotropy",

Powders and Grains 2005, 65-68, (2005) (Cover Image).

3. T. S. Majmudar, M. Sperl, S. Luding and R. P. Behringer “Jamming transition

in granular systems”, Physical Review Letters, 98, 058001 (2007) (Cover Article).

PDF of the Paper

4. C. J. Pipe, T. S. Majmudar, and G. H. McKinley “High Shear Rate Viscometry”,

Rheologica Acta, 47, 5, 621-642, (2008).

PDF of the Paper

5. R.P. Behringer, K.E. Daniels, T. S. Majmudar, and M. Sperl, Fluctuations, Correlations, and

Transitions in Granular Materials: Statistical Mechanics for a Non-Conventional System,

Phil. Trans. Roy. Soc. A – Math. Phy. and Eng. Sci., 366, 1865, 493-504, (2008).

PDF of the Paper

6. Jie Zhang, Trush Majmudar, and R.P. Behringer, “Force chains in a two-dimensional granular

pure shear experiment”, Chaos, 18, 041107-1, (2008).

PDF of the Paper

7. G. Lois, J. Zhang, T. S. Majmudar, S. Henkes, B. Chakraborty, C. S. O’Hern, R. P. Behringer,

“Stress correlations in granular materials: an entropic formulation”, Physical Review E , 80,

060303(R), (2009).

PDF of the Paper

8. J. Zhang, J. Ren, S. Farhadi, R. P. Behringer, T. S. Majmudar and A. Tordesillas, “Dense 2D

Granular Material Subject to Cyclic Pure Shear”, Powders and Grains 2009, 553—556,

(2009).

9. J. Zhang, R. P. Behringer, T. S. Majmudar and M. Sperl, “Experiments on Force Fluctuations

and the Jamming Transition”, Powders and Grains 2009, 527—530, (2009).

10. J. Zhang, T .S. Majmudar, A. Tordesillas, and R.P. Behringer, “Statistical properties of a 2D

granular material subjected to cyclic shear”, Granular Matter, 12, 159, (2010).

PDF of the Paper

11. J. Zhang, T. S. Majmudar, M. Sperl, and R. P. Behringer, “Jamming for a 2D granular

material”, Soft Matter, 6, 2982-2991, (2010).

PDF of the Paper

**Preprints:**

1. Trushant Majmudar, Matthieu Varagnat, and Gareth
McKinley, “Nonlinear Dynamics

of coiling in Viscoelastic Jets”,
To be submitted to Phys. Fluids (2010).

PDF of the paper

2. Matthieu Varagnat, Trushant Majmudar, and Gareth
McKinley, “The folding dynamics in

axi-symmetric jets of surfactant
fluids”, To be submitted to J. non-Newt. Fluid Mech. (2010).

PDF of the Paper

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