Abhik
Basu
Theoretical Condensed Matter
Physics Division
Saha Institute of Nuclear Physics
Calcutta
M.Sc. in Physics,
Department of Physics, Indian Institute of Science,
Bangalore (1996).
B.Sc. in Physics (Hons.), Presidency College,
Calcutta (1992).
E-mail: abhik.basu@saha.ac.in
Phone: 0091 33 2337 5345-49, extn.-3426
Fax: 0091 33 2337 4637
Professional experience: Alexander von
Humboldt Fellow (HMI, Berlin, 2003-2004), Distinguished PKS
Post-doctoral Fellow (MPIPKS, Dresden, 2004-2006).
Research Interests:
- Physics of soft matter and biological
systems:
Within the last few years, the
physics of soft condensed matter has become a rapidly expanding branch
of theoretical physics. This is mainly due to the recognition that
seemingly disparate phenomena in materials such as colloids, polymers
and liquid crystals, may be described by unified concepts taking into
account the importance of thermal fluctuations in these systems. The
softness of interactions in these systems leads to complex phase
behavior and dynamical phenomena which not only present challenges to
fundamental science, but which are also matter of technological
importance, e.g., dynamics of complex, and for the processing and
design of biocompatible materials. Soft matter systems provide
ideal testing grounds for non-equilibrium statistical mechanics -
theoretically as well as experimentally. While research on soft matter
has traditionally been focused on synthetic materials, rapid
developments in molecular biology have provided evidence that soft
interactions and fluctuation phenomena play a vital role in biology, in
particular on the level of the very fundamental processes such as
cytoskeletal organization, force generation by molecular motors,
membrane dynamics etc, pattern formations in living cells etc.
The emergence of complex patterns and correlated fuctuations are
characteristic features of dynamic processes in cells such as cell
locomotion and cell division, all of which represent out of equilibrium
processes. One of our central goals is to understand some of the
general physical principles governing cooperativity and collective
behavior of such processes at large time and length scales. In
particular, the general questions of how cells exert forces, and the
interplay between these forces and the underlying chemical reactions
which produce them, are being increasingly considered by biologists and
physicists alike. A prominent example of such systems is the collective
dynamics of cytoskeletal flaments and motor proteins, which
largelygovern cellular dynamics, inside a cell. It is believed that
general physics considerations and principles of nonequilibrium
statistical mechanics, and general properties of active materials
relevant for cellular processes will play an important role in the
broad understanding of theunderlying phenomena there. Our particular
interests involve theoretical understanding of the dynamics
cytoskeletons in vivo and in vitro experiments.There is a wealth of
data about interesting and complex processes in biological systems. Our
goal is to analyze these systems in an interdisciplinary collaboration
with scientists from all natural sciences. The vision is to understand
how physical laws govern the material properties, operation of
biochemical machinery, and the processing of information inside cells.
One of the great challenges will be to formulate theoretical concepts
which allow to study driven non-equilibrium systems with many
structural and regulatory components. This might shed some light on the
physical principles behind the hierarchical organization of living
system with a rather precise level of control at all levels of
hierarchy.
The cytoskeleton of a cell has interesting material properties: It is a
visco-elastic
material. The diffusion constant of a small bead attached to it
has been measured and has been found to deviate from the usual Einstein
relations, exhibiting anomalous diffusive
behaviour. We are interested to have a theoretical understanding
of this behaviour using the framework of non-equilibrium statistical
mechanics.
Snap shot of a bead attached to a
cytoskeleton
Mean square displacement of a bead
attached to a cytoskeleton executing diffusive dynamics
The problem of wetting of a surface by a flowing
liquid is important both theoretically and experimentally/industrially,
e.g., in a number of
practical situations such as paints, textile dyeing, metal or glass
anticorrosive coating, lubrication, gluing, plant treatment and
cosmetology.. The problem of wetting by a simple liquid is now greatly
understood in terms of the notion of interfacial tension or surface tension. Such questions
assume importance in view of recent exxperiments on spreading
of cells. However
probing wetting in such systems means we need to handle visco-elastic materials. These
have very unusual material properties: Their response to an external
perturbations (e.g., an applied force) cen be solid-like (elastic) or
fluid-like (viscous) depending upon the time scales of measurements.
Our goal is to examine the process of wetting by such visco-elastic
materials by extending the framework of wetting theories for simple
liquids.
Cell spreading with time
Experimental results on cell spreading
[time dependence of relative area of contact for various cells
(Chamaraux et al, PRL)]
Biological cells sustain their machanical stability in simple and
robust ways; at the same time they have extraordinary dynamical
abilities, e.g., movement. The basic structural elements making this
possible are semiflexible
(stiff) polymers which in the cytoskeleton are present in the form of
F-actins, intermediate filaments and microtubuli. Thes unusual
behaviour are responsible for many interesting properties of these
biopolymers, e.g., their static properties differ greatly from
usual (Gaussian) polymers.Two features of these polymers distinguish
them from most
other polymers we know: they have a high degree of stiffness which
supresses bending, and they are too a large degree inextensible. Many
of these properties are studied
experimentally, e.g., in optical and magnetic tweezers experiments and
light scattering experiments. The last one reveals informations about
dynamic structure factors. We plan to study the dynamics of
fluctuations in a stiff polymer with or without twists in various given
external conditions. We are
interested in the dynamical properties of such polymers under various
conditions like shear flows.
A
coarse-grained view of a semiflexible polymer in a shear flow
Dynamic of a semiflexible polymer in a sher
flow [Schroeder et al, PRL (2005)]
Measurement of the dynamic properties of a cell can provide important
information on its physical state. The dynamics of certain types of
motion of a cell and/or its structural components can be inferred from
the measurement of the intensity fluctuations in light scattered by the
cell. Changes in cellular dynamics, which reflect alterations in the
physical properties of the cell arising from biochemical modifications
or physiological changes, lead to changes in the temporal properties of
the intensity fluctuations. Measurement of the dynamic
properties of a cell can provide important information on its
physical
state. The dynamics of certain types of motion of a cell and/or its
structural components can be inferred from the measurement of the
intensity fluctuations in light scattered by the cell. Changes in
cellular dynamics, which reflect alterations in the physical properties
of the cell arising from biochemical modifications or physiological
changes, lead to changes in the temporal properties of the intensity
fluctuations. Intensity fluctuations of the scattered light are
characterised by appropriate auto-correlation functions. The
membrane of a erythrocyte or red blood cell is a thin material, only
about 5 nm tliick and essentially lamellar in structure. It
consists of a lipid bilayer (believed to be in a liquid phase) in which
macromolecules are incorporated. In addition there is also a spectrin
polymer nenvork attached to the inner layer through proteins. The
presence of the spectrin implies that unlike the phospholipid component
of a biological membrane, the composite red blood cell membrane
exhibits a shear modulus The shape of the cell is biconcave-discoid
under normal physiological conditions. In thin state the membrane
surface tension is very small and the red blood cells show a remarkable
flicker phenomenon, which can be seen by phase contrast
microscopy. This flicker is a purely physical phenomenon and is
believed to be due to fluctuations of the cell membrane. Flicker
phenomena observed in different mammal red blood cells show remarkable
similarity. Such studies yields informations about elastic
modulii of RBC membranes. We plan to study these phenomena from
perspectives of nonequilibrium statistical mechanics and
soft-matter physics.
Small-scale
structure of a cell membrane
More pictures of cell membranes
A coarse-grained
view of a membrane
Collaborators: Prof.
Erwin Frey (LMU, Munich), Prof. Jean-Francois Joannay (Institut
Curie, Paris), Prof.
Frank Juelicher (MPIPKS, Dresden), Prof.
Jacques Prost (ESPCI, Paris), Prof.
Sriram Ramaswamy (IISc, Bangalore), Mr. Rakesh
Chatterjee (SINP, Calcutta).
- Physics of driven nonequilibrium
systems:
Properties of superconductors in the presence of an externally imposed
constant electric field have been studied theoretically and
experimentally in quasi one-dimensional systems. No attempt have
been made to understand the effects of external fluctuating electric
fields in the bulk. Stability of equilibrium fixed points have been
studied in various models. For example, Taeuber considered
non-equilibrium generalizations of the O(N)-symmetric models and
studied the resulting non-equilibrium dynamics. Detailed balance
violations have been incorporated by introducing spatially anisotropic
forms for the noise correlations (equivalently, by having different
temperatures for different fields in the model). They examined, in a
renormalization group framework, the stability of the equilibrium
critical dynamics behaviour in the presence of detailed balance
violating noise of the type mentioned above. However, such noises, if
relevant would necessarily make the renormalized theory incompatible
with the O(N) symmetry of the unrenormalized theory. So far, no attempt
has been made to understand the relevance (in an RG sense) of detailed
balance violating aspects which are inconformity with the O(N)
symmetry. Such studies are physically relevant. For the case with N=2
such studies will have relevance for the problem of a superconductor
placed in fluctuating external electric fields.
Motor proteins play a key role in intracellular transport processes.
Theoretical modeling of such processes rely on a combination of step
processes
(TASEP) and bulk Langmuir kinetics. Effects of a single defect on the
transport processes has been discussed in Ref.\cite{frey2}. Such studies
have implications in understanding some diseases connected to motor
proteins. All these studies involve a single one-dimensional lattice.
However, real systems would involve several path ways for the motor
proteins (modeled here by 1d lattices). The presence of more than one
pathways open the possibility of motor proteins being able to avoid a
blockage (in the form of a defect) by jumping to a near by path. This
would reduce the effective strength of the defect thereby reducing the
possibility of any disease. However, theoretical studies involving
multiple lattices have not been done yet. Apart from their biological
implications such studies will shed further light in the understanding
of the non-equilibrium steady states of coupled systems as well as in
understanding the basics of Spintronics.
A two-channel TASEP
We are looking at the short range truly
self avoiding random walk in a field theoretic set up. We show
that at or below the upper critical dimension 2 for this problem there
are infinite number or marginal or relevant coupling constants present
in the theory. We, however, are able to demonstrate that a systematic
loop-expansion is, nevertheless, possible by using a functional
renormalization group (FRG) approach. We calculate the relevant scaling
exponents in an epsilon-expansion.
Collaborators: Prof.
Erwin Frey (LMU, Munich), Dr.
Anjan
Chandra (SINP, Calcutta), Mr. Tamoghna Das (SNBose
Centre, Calcutta),
Mr. Debarshee
Bagchi (SINP, Calcutta).
- Fluid and
magnetohydrodynamic turbulence:
In fluid dynamics, turbulence or turbulent flow is a
flow regime characterized by chaotic, stochastic property changes. This
includes low momentum diffusion, high momentum
convection, and rapid variation of pressure and velocity in space and
time. Flow that is not turbulent is called laminar flow. The
(dimensionless) Reynolds number characterizes whether flow conditions
lead to laminar or turbulent flow; e.g. for pipe flow, a Reynolds
number above about 4000 (A Reynolds number between 2100 and 4000 is
known as transitional flow) will be turbulent. At very low speeds the
flow is laminar, i.e., the flow is smooth (though it may involve
vortices on a large scale). As the speed increases, at some point the
transition is made to turbulent flow. In turbulent flow, unsteady
vortices appear on many scales and interact with each other. From the
perspectives of theoretical physics homogeneous and isotropic
turbulence are interesting since different order equal time structure functions
(these are
similar to correlation functions) exhibit universal (i.e.,
independent of viscosity and the details of forcing mechanism) spatial
scaling properties. Homogenous and isotropic turbulence can be realised
far away from the boundary of the system and at scales much smaller
than the forcing scale.
Magnetohydrodynamics
(MHD)
is the subject which studies the dynamics of electrically conducting
quasi-neutral fluids. Examples of such fluids include plasmas, liquid
metals, and
salt water.We are interested in studying turbulence in such systems.
Natural occurance of such systems include solar surface, solar wind,
ionosphere, laboratory plasmas etc. Similar to fluid turbulence
structure functions in MHD turbulence shows universal properties. We
plan to analyse the universal properties of nonequilibrium steady
states of driven Magnetohydrodynamic (MHD) turbulence in three
dimensions. We elucidate the dependence of various phenomenologically
important dimensionless constants on the symmetries of the two-point
correlation functions. We, for the first time, also suggest the
intriguing possibility of multiscaling universality class varying
continuously with certain dimensionless parameters. The experimental
and theoretical implications of our results are being considered.
Click here for a picture of turbulence on the solar
surface (top to bottom: velocity fields, magnetic fields and
local temperature)
Collaborators: Prof. Rahul Pandit
(IISc, Bangalore), Mr. Samriddhi Sankar Ray
External funding for research: DST
Fast Track Project (2007)
Publications:
- Anomalous
diffusion in an active polar gel, A. Basu, J F
Joanny J Juelicher and J Prost, manuscript in preparation.
- Scaling
and universality in coupled driven diffusive models, A
Basu and E Frey, manuscript in preparation
- Dynamics
of a semi-flexible polymer in a shear flow, A Basu and E
Frey, manuscript in preparation
- Structure-function
Hierarchy for the Burgers-model Analog for
Magnetohydrodynamic Turbulence, A Basu and R Pandit, manuscript
in
preparation
- Perspectives
on the mode-coupling approximation for the dynamics
of interacting brownian particles, A Basu and S Ramaswamy, J. Stat.
Mech., stacks.iop.org/JSTAT/2007/P11003 (2007)
- Thermal and non-thermal
fluctuations in active polar gels, A Basu, J F Joanny, F
Juelicher and J Prost, submitted to Eur.
Phys. J E (2008).
- Novel multiscaling in
magnetohydrodynamic turbulence, A Basu, manuscript in
preparation
- Neural
network modeling, B K Chakrabarti and A Basu, Prog. Brain res. Vol. 168
(2008) pp 155-168
- Symmetries and novel universal
properties of turbulent hydrodynamics in a binary fluid mixture,
A
Basu, J. Stat. Mech. (2006)
- Alfven waves
and
dissipation range asymptotics in Magnetohydrodynamic turbulence:
Scaling and multiscaling, A. Basu, the proceedings of the
National
Conference on Nonlinear Science and Dynamics, Aligarh Muslim
University, Aligarh, February 24-26 (2005)
- Universal
properties of
three-dimensional magnetohydrodynamic turbulence: Do Alfven waves
matter?, A. Basu and J K Bhattacharjee, J Stat Mech, P07002 (2005)
- Dynamo
mechanism: Effects of correlations and viscosities,
A. Basu, Eur Phys J B,
38, 117 (2004)
- Novel
universality classes of coupled driven
diffusive systems, A. Basu and E. Frey, Phys. Rev. E (rap. com.), 69,
015101 (R) (2004)
- Scaling
in a temperature quench in systems with a Lifshitz
point: Nonconserved and conserved order parameters, A.
Basu and J K Bhattacharjee, J Phys A,
37,
1111 (2004)
- Statistical
properties of driven Magnetohydrodynamic turbulence
in three dimensions: Novel universality, A. Basu, Europhys.
Lett., 65, 505 (2004)
- Shell-model
studies of Magnetohydrodynamic Turbulence in three
dimensions, A Basu and R Pandit, the proceedings of the National
Conference on Nonlinear Science and Dynamics, IIT Kharagpur,
December
28-30, 2003.
- Phase
diagram of a two species model with a linear
instabilities, S Ramaswamy, M Barma, D Das and A Basu, Phase
Transitions, 75, 363 (2002)
- Weak and
strong dynamic scaling in a one-dimensional driven
coupled-field model: Effects of kinematic waves, D Das, A Basu,
M Barma
and S Ramaswamy, Phys Rev E,
64, 021402 (2001)
- Phase
transitions and noise crosscorrelations in a model of
directed polymers in a disordered medium, A Basu, Phys. Rev. E, 62,
4675 (2000)
- Coupled
non-equilibrium growth equations: Self consistent mode
coupling using vertex renormalisation, A Kr Chattopadhyay, A
Basu and J
K Bhattacharjee, Phys. Rev. E
61, 2086 (2000)
- Inequivalence
of ensembles in a Driven Diffusive Lattice Gas, M
Acharya, A Basu, R Pandit and S Ramaswamy, Phys. Rev. E, 61, 1139
(2000)
- Decaying
magnetohydrodynamics: Effects of initial conditions, A
Basu, Phys. Rev. E, 61,
1407 (2000)
- Mean
Magnetic Field and Noise Cross-Correlation in
Magnetohydrodynamic Turbulence: Results from a One-Dimensional Model,
A. Basu, J K Bhattacharjee and S Ramaswamy, Eur. Phys. J B, 9,
425 (1999)
- The
dynamo effect - A dynamic renormalisation group approach, A.
Basu and J K Bhattacharjee, Europhys. Lett., 46, 183 (1999);
Erratum 47, 1 (1999)
- Multiscaling
in Models of Magnetohydrodynamic Turbulence, A
Basu, A Sain, S K Dhar and R Pandit, Phys. Rev. Lett., 81, 2687
(1998)
- The
Screw Dynamo and the Generation of Magnetic Fields, A
Basu, Phys. Rev. E, 56, 2869 (1997).
Teaching: Condensed
Matter Physics
Assignment I
RTCM