Research interest

Biophysics

Cell and Tissue Mechanics:
    
Most cell types in human body stick to other cells or to the extracellular matrix in order to communicate and 
maintain structural integrity. At the same time, they respond quickly to changes in their environment. This 
corresponds to a continuous remodeling of cell-cell and cell-matrix contacts and the structures they are 
attached to. We focus at developing a quantitative modeling framework to deal with the structural aspects 
of cell adhesion. Such a framework has to integrate the cytoskeletal dynamics, adhesion cluster dynamics, 
and the extracellular matrix. 

Cell Division:
                                
Mitotic cell division generates two identical daughter cells from a single cell using a complex machinery called 
"mitotic spindle" which essentially helps the chromosomes to segregate properly. Dynamic filaments known as 
Microtubules (MT),  "Search and Capture" the chromosomes to assemble the "Mitotic spindle". In order to 
proceed through the mitosis MTs should be properly "attached" to the chromosomes - failing to which causes cell 
death and even cancer. Our "Search and Capture" model can predict the probability of erroneous attachments and
test the effectivness of different error correction hypothesis.


Statistical Mechanics

Percolation in tumor vasculature:
               
Tumor induced angiogenesis is the formation of new blood vessels around the tumor from pre-existing capillaries in 
a hypoxic (O2 depleted) microenvironment. Hypoxia induces growth factor synthesis and release from tumor cells 
which act on endothelial cells or nearby blood vessels. Angiogenic sprouting, new vessel formation and vessel dilation 
is the result of this interaction leading to favorable tumor growth conditions. We introduce a stochastic model to describe 
vascularization and necrotic regions develops outside and inside the tumor respectively. A percolation transition is found 
for vessel collapse inside the tumor as a function of angiogenic probability. Applying blood flow one finds a completely 
different evolution morphology of the tumor-vascular system and the results resembles to the experimental observations.

Coarsening in disordered media:
                                         
A homogeneous binary mixture becomes thermodynamically unstable if it is rapidly quenched below the coexistence curve. 
The subsequent far-from-equilibrium evolution of the system is characterized by the emergence and growth of domains 
enriched in the new equilibrium phases. There is a good understanding of domain-growth kinetics in pure and isotropic 
systems. In our research, we focus on domain growth in ferromagnets and binary alloys with quenched disorder in the 
form of random exchange interactions as well as site dilution. At early times, domain coarsening is not affected by disorder. 
Then, there is a crossover to a disorder-affected regime, which occurs earlier for higher disorder amplitudes. Kinetics is 
slowed down due to the effect of random bonds or non-magnetic atoms, since both these factor reduces the driving force 
responsible for domain growth. Near the percolation threshold, this effect is quite large. However in all cases domain 
evolutions are consistent with power-law growth with a variable exponent. These results are interpreted in the context of 
disorder barriers with a logarithmic dependence on the domain size.
Dr. Raja Paul
 Assistant Professor
 
Contact:
Indian Association for the Cultivation of Science
Department of Solid State Physics
Jadavpur, Kolkata 700 032, India 
Phone No: +91 33 2473 4971 (ext 310) 
E-mail: ssprp [ AT ] iacs.res.in

Education: 
Postdoc (2007-2009), University of California Davis, U.S.A.
Postdoc (2005-2007), University of Heidelberg, Germany, 
Ph.D. (2005), University of Saarland, Germany
M..Sc. (2000), Physics, Jawaharlal Nehru University, New Delhi                            

Publications:
1  R. Paul, R.  Wollman, W. T. Silkworth, I. K. Nardi, D. Cimini,  A. Mogilner,
Computer simulations predict that chromosome movements and rotations accelerate mitotic spindle assembly without compromising accuracy,
PNAS (2009), in press.
2 N. P. Ferenz, R. Paul, C. Fagerstrom, A. Mogilner, P. Wadsworth,
Eg5/Dynein antagonism during bipolar spindle assembly formation requires overlapping centrosomal microtubules,
Current Biol. (2009), in press
3 R. Paul,
Flow-correlated dilution of a regular network leads to a percolating network during tumor induced angiogenesis,
Eur. Phys. J. E (2009),  in press.
4 R. Paul and U.S. Schwarz.
Pattern formation and force generation by cell ensembles in a filamentous matrix. Proceedings of the IUTAM Symposium on Cellular, Molecular  and Tissue Mechanics, 
in press, Springer (2009).
 5 R. Paul, P. Heil, U. Schwarz and J. Spatz,
Propagation of mechanical stress through the actin cytoskeleton towards focal adhesions: model and experiment,
Biophys. J. , 94:1470-1482, (2008).
 6 R. Paul, J.-D. Noh, G. Schehr, H. Rieger,
Computer simulations of phase transitions and dynamics in confined systems,
Z. Phys. Chem., 222, 433 (2008) 
 7 R. Paul, A. Gambassi and G. Schehr,
Dynamic crossover in the global persistence at criticality,
Europhys. Lett. 78, 10007 (2007).
 8 R. Paul, G. Schehr and H. Rieger,
Super-Aging in two-dimensional random ferromagnets,
Phys. Rev. E 75, 030104(R) (2007).
 9 G. Schehr and R. Paul,
Non-equilibrium critical dynamics in disordered ferromagnets,
J. Phys: Conf. Series 40 27-35 (2006).
 10 R. Paul and G. Schehr,
Non Markovian persistence in the diluted Ising model at criticality,
Europhys. Lett. 72(5), 719 (2005).
 11 R. Paul and H. Rieger,
Condensation Phenomena in Nanopores - a Monte Carlo Study,
J. Chem. Phys. 123, 024708 (2005).
 12 R. Paul, S. Puri and H. Rieger,
Domain Growth in Ising Systems with Quenched Disorder,
Phys. Rev. E 71, 061109 (2005).
 13 G. Schehr and R. Paul,
Universal aging properties at a disordered critical point,
Phys. Rev. E 72, 016105 (2005).
 14 G. Schehr, R. Paul, H. Rieger,
Growing length scales in 2d disordered systems,
Prog. Theor. Phys. Suppl., 157, 111 (2005)
 15 R. Paul, S. Puri and H. Rieger,
Domain growth in random magnets,
Europhys. Lett. 68(6), 881 (2004).
 16 R. Paul, M. Alava and H. Rieger,
Low temperature properties of the random field Potts chain, 
Eur. Phys. J. B 30, 357 (2002).
last updated on September 17, 2009

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