Dr. Ajanta Bhowal Acharyya

M.Sc. (C.U.), Ph.D. S.I.N.P.(C.U.)
Associate Professor

Department: Physics
About me

Academic qualification: 

 (a) M.Sc (Spectroscopy), 1988 (Exam. held in 1989),    University of Calcutta, 1st class.

 (b) Post M.Sc associateship  course (1989-90) in Saha Institute of Nuclear Physics. 

 (c) Ph.D, in Saha Institute of Nuclear Physics, thesis submitted (to the University of Calcutta) on 22nd September, 1995  degree awarded on 29th June 1996.

 (d) National Scholarship etc: Obtained CSIR-UGC NET Scholarship in 1989. 

 (e) Postdoctoral research fellow, 1996-1997, SINP, Calcutta.

 (f) Present Position: Assistant Professor, Department of Physics, Lady Brabourne College, Calcutta.


Expertise : Teaching—UG & PG

  (i) UG: Teaching experiences  in Thermodynamics, Electrodynamics, Statistical Mechanics, Solid State Physics and few experimental techniques and Computational methods (FORTRAN) in undergraduate level. 

  (ii) PG Level:  Teaching  Statistical Mechanics and Computational Methods in Postgraduate level.


Research details

Brief description of  research work (Phd):

A symmetric fixed point of a four dimensional reversible mapping can loose its stability due to the collision of two pairs of multipliers on the unit 

circle and then moving away to the complex plane in opposite directions along two conjugate rays. The effect of such collisions, at an irrational angle (i.e., incommensurable with $pi$), on the behaviour of invariant curves(IC) around that symmetric fixed point describes the 'reversible Hopf bifurcation' (or Reversible Naimark Sacker bifurcation). 

We have studied exhaustively the various aspects of the reversible 

Hopf bifurcation in a family of four dimensional reversible maps[1-3].

Instead of an  irrational angle if two pairs of multipliers collide at or near a rational angle.

 at  exp(ωi) with ω =2π p/q (p,q mutually prime), then q-periodic orbits are generally found to bifurcate and it is termed as resonant collision of  order q.  We have then studied in details the bifurcation of periodic orbits (period 2 to 6)  as a result of resonant collision near rational angles [4-5].


Current research interests 

(A) The concept of Self Organised Criticality, introduced by BTW in terms of a cellular autamata model, is expected to be the underlying

cause of a large class of phenomena involving dissipative, nonlinear transport in open systems.  We studied the damage spreading  in BTW model[7].

We have also studied the onsets of avalanches and dissipations in the subcritical region of the BTW model [8]. Studied extensively the 

statistical behaviour of BTW model in SOC state.


(B)  The experimental data, which always includes some noise, must be preprocessed to reduce the noise before characterisation. There are various method for reducing noise in the time series whose underlying dynamical behaviour can be characterised by low dimensional chaos. We are trying to develop a better method for noise reduction following the main idea of Schreibber and Grassberger [Phys. lett. A 160 (1991) 411].

Our method [9]  is better in a sense that it gives better 'cleanliness' using smaller no of data.


(C) In Ising model, spontaneous magnetization decreases continuously as temperature increases and above a particular temperature, known as critical temperature,  magnetization vanishes.. Near the transition temperature some physical quantities show power law behavior, which are characterized by a set of critical exponents. This critical exponents are calculated numerically with the help of mean field equation of state of Ising Ferromagnet and compared with the analytically estimates values.

The dynamical behaviour of Ising ferromagnets in meanfield approximation is also studied.

Publications
1. A.Lahiri, A.Bhowal, T.K.Roy and M.B.Sevryuk, "Stability of invarriant curves in 4-D  reversible  maps  near  1:1  resonance." Physica-D 63 (1993),99. 


2. A.Bhowal, T.K.Roy and A.Lahiri, "Small angle Krein collision in  a family of 4-D reversible maps", Phys Rev E ,47(1993),3932.


3. A.Bhowal, T.K.Roy and A.Lahiri, "Hopf bifurcation in four-dimensional reversible maps and renormalisation equations", Phys-Lett A,179(1993),9.


4. A.Lahiri, A.Bhowal and T.K.Roy  "Fourth Order Resonant Collisions of Multipliers in Reversible Maps: 
 Period-4 Orbits and Invariant Curves", Physica D, 85 (1995), 10.


5. A. Lahiri, A. Bhowal and T.K. Roy, "Resonant Collision in 4D Reversible Maps, a description scenarios",
Physica D (1998) 112, 95.


6. A. Lahiri, T. K. Roy  and A. Bhowal, "Exotic Spectra, Wavefunctions and Transport in Incommensurate Lattices",
Pramana, 48, (1997), 555.


7. A. Bhowal, Damage spreading in the 'sandpile' model of SOC, Physica A,  247 (1997) 327


8. A. Bhowal, Onsets of avalanches in the BTW model, Physica A, 253 (1998) 301

9. A. Bhowal and T. K. Roy,Reduction  of Noise in Chaotic Time series Data,    Pramana, 52 No-1(1999),25.


10. M. Acharyya and A. Bhowal Acharyya, Modelling and Computer simulation of an insurance policy: A search for maximum profit, Int. J. Mod. Phys. C  14 (2003) 1041


11. M. Acharyya and A. Bhowal Acharyya, Inflection point as a manifestation of tricritical point in Ising meanfield dynamics, Comm. Comp. Phys. 3 (2008) 397


12. M Acharyya and A. Bhowal Acharyya, Critical Slowing Down along the dynamic phase boundary in Ising meanfield dynamics, Int. J. Mod. Phys. C  21 (2010) 481


13. A. Bhowal Acharyya, Cluster statistics in BTW automata, Acta Physica Polonica B, 42 (2011) 19.(Impact Factor: 1.01)

14. M Acharyya and A. Bhowal Acharyya,Evidence of invariance of time scale at critical point in Ising meanfield equation of state, Comm. Theo Phys. 55 (2011) 1109.

15. A. Bhowal Acharyya and  M Acharyya, Bose Einstein Condensation in arbitrary dimension,Acta Physica Polonica B, 43 (2012) 1805.(Impact Factor: 1.01)

16. A partial list of citation of my work

1. T. J. Bridges and J. E. Furter, Singularity Theory and
Equivariant Maps, Lecture Notes in Mathematics,
Vol 1558, Springer-Verlag., 1993

2.Subharmonic branching at a reversible 1:1 resonance 
Maria-Cristina Ciocci 

3. Time-Reversal Symmetry in Dynamical Systems: A Survey 
Jeroen S. W. Lamb, John A. G. Roberts 

4.Bayram Deviren, Mustafa Keskin, Osman Kanko, Dynamic phase transitions in the kinetic mixed spin-1/2 and
spin-5/2 Ising model under a time dependent oscillating magnetic field, Phase Transitions 01/2010; 83(7) 526-542.

5.M.B. Sevryuk. The iteration approximation decoupling in the reversible KAM theory, Chaos 10/1995; 5(3):552-565

17. Distinction and achievement


18. Any other


School/Workshop/Seminar attended:

(A). "Introductory Course on Chaotic Dynamics" held on 
Inter University Consortium, Indore, India, March 1992.

(B). "Computational Aspects in Chaos and Nonlinear Dynamics",
held on Department of Physics, Maharajas College, Cochin, India, March
21-25, 1994.

(C). "Local and Variational Methods in the Study of Hamiltonian
System", International Center for Theoretical Physics, Trieste, Italy,
October 1994.


(d)Scotish Church
(e)Laser Symposium
(f)Vivekananda
(g)Solar Cell at JU
(h)INO

Talk Delivered under the Theoretical Physics Seminar circuit programme (1995) at

1. University of Pune 
2. Bharati Darshan University
3. Indian Institute of Astrophysics (Bangalore)



19.Project Supervision of PG Students

1. Poonam Das (2011) Study of Critical behaviour of Ising Ferromagnet with the help of mean field theory developed by Bragg William.

2. Chhandita Halder (2011) on ' Ferro-Para Transition as an example of critical phenomenon and estimation of the critical exponent.'

3. Rishmita  Ghosh (2011) on Estimation of Critical Exponents from Bragg William mean field equation of state of Ising Ferromagnet.

4. Kashmira Khatoon (2013) on 'Study of Ferro-para transition using Bragg William mean field approximation'.
5. Swarnali Bose (2013) on 'Kinetic Ising Model in mean field approximation.'