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


Contact :

Department of Solid State Physics
Indian Association for the Cultivation of Science
Jadavpur, Kolkata 700 032, India

E-mail: ssprp [ AT ] iacs.res.in
Phone: +91-33-24734971 (Ext. 1310 (Office), 2114 (Lab))
Fax: +91-33-24732805


Publications:
1 Vinogradova T, R. Paul, Grimaldi AD, Loncarek J, Miller PM, Yampolsky D, Magidson V, Khodjakov A, Mogilner A, Kaverina I.,
Concerted effort of centrosomal and Golgi-derived microtubules is required for proper Golgi complex assembly but not maintenance,
Mol. Biol. Cell, 23: 820-833 (2012).
2 William T. Silkworth, Isaac K. Nardi, R. Paul, Alex Mogilner, Daniela Cimini,
Timing of centrosome separation is important for accurate chromosome segregation,

Mol. Biol. Cell, 23: 401-411 (2012).
3 Valentin Magidson, Christopher B. O'Connell,  R. Paul, Jadranka Loncarek, Alex Mogilner and Alexey Khodjakov,
Spatial arrangement of chromosomes during prometaphase accelerates spindle assembly, Cell, 146: 555-567 (2011).
4  R. Paul,
Modeling Biological Cells,
Chem. Modell., 9, 61-91 (2012)
5  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, 106: 15708-1513 (2009)
6 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., 19 : 1833-1838 (2009)
7 R. Paul,
Flow-correlated dilution of a regular network leads to a percolating network during tumor induced angiogenesis,
Eur. Phys. J. E 30, 101-114 (2009)
8 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).
 9 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).
 10 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) 
 11 R. Paul, A. Gambassi and G. Schehr,
Dynamic crossover in the global persistence at criticality,
Europhys. Lett. 78, 10007 (2007).
 12 R. Paul, G. Schehr and H. Rieger,
Super-Aging in two-dimensional random ferromagnets,
P
hys. Rev. E 75, 030104(R) (2007).
 13 G. Schehr and R. Paul,
Non-equilibrium critical dynamics in disordered ferromagnets,
J. Phys: Conf. Series 40 27-35 (2006).
 14 R. Paul and G. Schehr,
Non Markovian persistence in the diluted Ising model at criticality,
Europhys. Lett. 72(5), 719 (2005).
 15 R. Paul and H. Rieger,
Condensation Phenomena in Nanopores - a Monte Carlo Study,
J. Chem. Phys. 123, 024708 (2005).
 16 R. Paul, S. Puri and H. Rieger,
Domain Growth in Ising Systems with Quenched Disorder,
Phys. Rev. E 71, 061109 (2005).
 17 G. Schehr and R. Paul,
Universal aging properties at a disordered critical point,
Phys. Rev. E 72, 016105 (2005).
 18 G. Schehr, R. Paul, H. Rieger,
Growing length scales in 2d disordered systems,
Prog. Theor. Phys. Suppl., 157, 111 (2005)
 19 R. Paul, S. Puri and H. Rieger,
Domain growth in random magnets,
Europhys. Lett. 68(6), 881 (2004).
 20 R. Paul, M. Alava and H. Rieger,
Low temperature properties of the random field Potts chain, 
Eur. Phys. J. B 30, 357 (2002).