K. M. Aggarwal

Queen's University Belfast, Béal Feirste, N Ireland, United Kingdom

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Publications (218)610.39 Total impact

  • K M Aggarwal, F P Keenan
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    ABSTRACT: Energy levels and radiative rates are reported for transitions in Cl-like W LVIII. Configuration interaction (CI) has been included among 44 configurations (generating 4978 levels) over a wide energy range up to 363 Ryd, and the general-purpose relativistic atomic structure package ({\sc grasp}) adopted for the calculations. Since no other results of comparable complexity are available, calculations have also been performed with the flexible atomic code ({\sc fac}), which help in assessing the accuracy of our results. Energies are listed for the lowest 400 levels (with energies up to $\sim$ 98 Ryd), which mainly belong to the 3s$^2$3p$^5$, 3s3p$^6$, 3s$^2$3p$^4$3d, 3s$^2$3p$^3$3d$^2$, 3s3p$^4$3d$^2$, 3s$^2$3p$^2$3d$^3$, and 3p$^6$3d configurations, and radiative rates are provided for four types of transitions, i.e. E1, E2, M1, and M2. Our energy levels are assessed to be accurate to better than 0.5%, whereas radiative rates (and lifetimes) should be accurate to better than 20% for a majority of the strong transitions.
    Atomic Data and Nuclear Data Tables. 06/2014;
  • KM Aggarwal, FP Keenan
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    ABSTRACT: Energies for the lowest 56 levels, belonging to the 3s$^2$3p, 3s3p$^2$, 3p$^3$, 3s$^2$3d, 3s3p3d, 3s$^2$4$\ell$ and 3s$^2$5$\ell$ configurations of Si II, are calculated using the {\sc grasp} (General-purpose Relativistic Atomic Structure Package) code. Analogous calculations have also been performed (for up to 175 levels) using the Flexible Atomic Code ({\sc fac}). Furthermore, radiative rates are calculated for all E1, E2, M1 and M2 transitions. Extensive comparisons are made with available theoretical and experimental energy levels, and the accuracy of the present results is assessed to be better than 0.1 Ryd. Similarly, the accuracy for radiative rates (and subsequently lifetimes) is estimated to be better than 20% for most of the (strong) transitions. Electron impact excitation collision strengths are also calculated, with the Dirac Atomic R-matrix Code ({\sc darc}), over a wide energy range up to 13 Ryd. Finally, to determine effective collision strengths, resonances are resolved in a fine energy mesh in the thresholds region. These collision strengths are averaged over a Maxwellian velocity distribution and results listed over a wide range of temperatures, up to 10$^{5.5}$ K. Our data are compared with earlier $R$-matrix calculations and differences noted, up to a factor of two, for several transitions. Although scope remains for improvement, the accuracy for our results of collision strengths and effective collision strengths is assessed to be about 20% for a majority of transitions.
    04/2014;
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    K. M. Aggarwal, F. P. Keenan
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    ABSTRACT: We report calculations of energy levels, radiative decay rates, and lifetimes for transitions among the 3s$^2$3p$^5$, 3s3p$^6$, and 3s$^2$3p$^4$3d configurations of Cl-like W LVIII. The general-purpose relativistic atomic structure package (GRASP) has been adopted for our calculations. Comparisons are made with the most recent results of Mohan et al. [Can. J. Phys. {\bf 92} (2014) xxx] and discrepancies in lifetimes are noted, up to four orders of magnitude in some instances. Our energy levels are estimated to be accurate to better than 0.5\%, whereas results for radiative rates and lifetimes should be accurate to better than 20\%.
    01/2014;
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    K. M. Aggarwal, F. P. Keenan
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    ABSTRACT: Energy levels, radiative rates and lifetimes are calculated among the lowest 98 levels of the n <= 4 configurations of Be-like Al X. The GRASP (General-purpose Relativistic Atomic Structure Package) is adopted and data are provided for all E1, E2, M1 and M2 transitions. Similar data are also obtained with the Flexible Atomic Code (FAC) to assess the accuracy of the calculations. Based on comparisons between calculations with the two codes as well as with available measurements, our listed energy levels are assessed to be accurate to better than 0.3%. However, the accuracy for radiative rates and lifetimes is estimated to be about 20%. Collision strengths are also calculated for which the Dirac Atomic R-matrix Code (DARC) is used. A wide energy range (up to 380 Ryd) is considered and resonances resolved in a fine energy mesh in the thresholds region. The collision strengths are subsequently averaged over a Maxwellian velocity distribution to determine effective collision strengths up to a temperature of 1.6x10$^7$ K. Our results are compared with the previous (limited) atomic data and significant differences (up to a factor of 4) are noted for several transitions, particularly those which are not allowed in jj coupling.
    11/2013;
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    KM Aggarwal, FP Keenan
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    ABSTRACT: We report calculations of energy levels, radiative rates, oscillator strengths and line strengths for transitions among the lowest 231 levels of Ti VII. The general-purpose relativistic atomic structure package ({\sc grasp}) and flexible atomic code ({\sc fac}) are adopted for the calculations. Radiative rates, oscillator strengths and line strengths are provided for all electric dipole (E1), magnetic dipole (M1), electric quadrupole (E2) and magnetic quadrupole (M2) transitions among the 231 levels, although calculations have been performed for a much larger number of levels (159,162). In addition, lifetimes for all 231 levels are listed. Comparisons are made with existing results and the accuracy of the data is assessed. In particular, the most recent calculations reported by Singh {\em et al} [Can J. Phys. {\bf 90} (2012) 833] are found to be unreliable, with discrepancies for energy levels of up to 1 Ryd and for radiative rates of up to five orders of magnitude for several transitions, particularly the weaker ones. Based on several comparisons among a variety of calculations with two independent codes, as well as with the earlier results, our listed energy levels are estimated to be accurate to better than $1\%$ (within 0.1 Ryd), whereas results for radiative rates and other related parameters should be accurate to better than $20\%$.
    Physica Scripta 11/2013; · 1.03 Impact Factor
  • Source
    K. M. Aggarwal, F. P. Keenan
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    ABSTRACT: We report calculations of energy levels and oscillator strengths for transitions in W XL, undertaken with the general-purpose relativistic atomic structure package ({\sc grasp}) and flexible atomic code ({\sc fac}). Comparisons are made with existing results and the accuracy of the data is assessed. Discrepancies with the most recent results of S. Aggarwal et al. [Can. J. Phys. {\bf 91} (2013) 394] are up to 0.4 Ryd and up to two orders of magnitude for energy levels and oscillator strengths, respectively. Discrepancies for lifetimes are even larger, up to four orders of magnitude for some levels. Our energy levels are estimated to be accurate to better than 0.5% (i.e. 0.2 Ryd), whereas results for oscillator strengths and lifetimes should be accurate to better than 20%.
    Canadian Journal of Physics 10/2013; 92(6). · 0.90 Impact Factor
  • KM Aggarwal, FP Keenan
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    ABSTRACT: We report calculations of energy levels, radiative rates, oscillator strengths and line strengths for transitions among the lowest 345 levels of Ti X. These include 146 levels of the $n \le$ 3 configurations and 86 of 3s$^2 4\ell$, 3s$^2 5\ell$ and 3s3p4$\ell$, plus some of the 3s$^2 6\ell$, 3p$^2 4\ell$ and 3s3p5$\ell$ levels. The general-purpose relativistic atomic structure package ({\sc grasp}) and flexible atomic code ({\sc fac}) are adopted for the calculations. Radiative rates, oscillator strengths and line strengths are provided for all electric dipole (E1), magnetic dipole (M1), electric quadrupole (E2) and magnetic quadrupole (M2) transitions among the 345 levels, although calculations have been performed for a much larger number of levels. Comparisons are made with existing results and the accuracy of the data is assessed. Additionally, lifetimes for all 345 levels are listed. Extensive comparisons of lifetimes are made for the lowest 40 levels, for which discrepancies with recent theoretical work are up to 30%. Discrepancies in lifetimes are even larger, up to a factor of four, for higher excited levels. Furthermore, the effect of large CI is found to be insignificant for both the energies and lifetimes for the lowest 40 levels of Ti X which belong to the 3s$^2$3p, 3s3p$^2$, 3s$^2$3d, 3p$^3$ and 3s3p3d configurations. However, the contribution of CI is more appreciable for the energy levels and radiative rates among higher excited levels. Our listed energy levels are estimated to be accurate to better than 1% (within 0.1 Ryd), whereas results for other parameters are probably accurate to better than 20%.
    07/2013;
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    K.M. Aggarwal, F.P. Keenan, A.Z. Msezane
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    ABSTRACT: Energy levels and radiative rates for fine-structure transitions in nickel ions (Ni XIII–XVI) have been calculated using the GRASP code. Configuration interaction and relativistic effects have been included, and comparisons are made with available data. Energy levels and radiative rates are tabulated for transitions among the 48, 43, 32, and 84 levels of Ni XIII, Ni XIV, Ni XV, and Ni XVI, respectively. The energy levels are assessed to be accurate to better than 5% for a majority of levels, while oscillator strengths for all strong transitions are accurate to better than 20%.
    Atomic Data and Nuclear Data Tables 07/2013; 85(2):453-494. · 1.00 Impact Factor
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    ABSTRACT: The main populating and depopulating mechanisms of the excited energy levels of ions in plasmas with densities <1023-1024 m-3 are electron collisional excitation from the ion's ground state and radiative decay, respectively, with the majority of the electron population being in the ground state of the ionization stage. Electron collisional ionization is predominately expected to take place from one ground state to that of the next higher ionization stage. However, the question arises as to whether, in some cases, ionization can also affect the excited level populations. This would apply particularly to those cases involving transient events such as impurity influxes in a laboratory plasma. An analysis of the importance of ionization in populating the excited levels of ions in plasmas typical of those found in the edge of tokamaks is undertaken for the C IV and C V ionization stages. The emphasis is on those energy levels giving rise to transitions of most use for diagnostic purposes. Carbon is chosen since it is an important contaminant of JET plasmas; it was the dominant low Z impurity before the installation of the ITER-like wall and is still present in the plasma after its installation. Direct electron collisional ionization both from and to excited levels is considered. Distorted-wave Flexible Atomic Code calculations are performed to generate the required ionization cross sections, due to a lack of atomic data in the literature.
    Journal of Physics B Atomic Molecular and Optical Physics 05/2013; 46(3). · 2.03 Impact Factor
  • Kanti M Aggarwal, Francis P Keenan
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    ABSTRACT: We report calculations of energy levels, radiative rates and electron impact excitation cross sections and rates for transitions in He-like Fe XXV, Co XXVI, Ni XXVII, Cu XXVIII and Zn XXIX. The grasp (general-purpose relativistic atomic structure package) is adopted for calculating energy levels and radiative rates. For determining the collision strengths and subsequently the excitation rates, the Dirac atomic R-matrix code (darc) is used. Oscillator strengths, radiative rates and line strengths are reported for all E1, E2, M1 and M2 transitions among the lowest 49 levels of each ion. Additionally, theoretical lifetimes are listed for all 49 levels of the above five ions. Collision strengths are averaged over a Maxwellian velocity distribution and the effective collision strengths obtained listed over a wide temperature range up to 107.7 K. Comparisons are made with similar data obtained using the flexible atomic code (fac) to highlight the importance of resonances, included in calculations with darc, in the determination of effective collision strengths. Discrepancies between the collision strengths from darc and fac, for some transitions, are also discussed. Finally, discrepancies between the present results of effective collision strengths with the darc code and earlier semi-relativistic R-matrix data are noted over a wide range of electron temperatures for many transitions in all ions.
    Physica Scripta 04/2013; 87(5):055302. · 1.03 Impact Factor
  • Kanti M Aggarwal, Francis P Keenan
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    ABSTRACT: We report calculations of energy levels, radiative rates and electron impact excitation cross sections and rates for transitions in He-like Ga XXX, Ge XXXI, As XXXII, Se XXXIII and Br XXXIV. The grasp (general-purpose relativistic atomic structure package) is adopted for calculating energy levels and radiative rates. For determining the collision strengths, and subsequently the excitation rates, the Dirac atomic R-matrix code (darc) is used. Oscillator strengths, radiative rates and line strengths are reported for all E1, E2, M1 and M2 transitions among the lowest 49 levels of each ion. Additionally, theoretical lifetimes are provided for all 49 levels of the above five ions. Collision strengths are averaged over a Maxwellian velocity distribution and the effective collision strengths obtained listed over a wide temperature range up to 108 K. Comparisons are made with similar data obtained using the flexible atomic code (fac) to highlight the importance of resonances, included in calculations with darc, in the determination of effective collision strengths. Discrepancies between the collision strengths from darc and fac, particularly for some forbidden transitions, are also discussed. Finally, discrepancies between the present results for effective collision strengths with the darc code and earlier semi-relativistic R-matrix data are noted over a wide range of electron temperatures for many transitions in all ions.
    Physica Scripta 03/2013; 87(4):045304. · 1.03 Impact Factor
  • K. M. Aggarwal, F. P. Keenan
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    ABSTRACT: Energy levels and radiative rates for E1, E2, M1, and M2 transitions among the lowest 24 levels, belonging to the n <= 5 configurations of Ar XVI and Fe XXIV, are calculated using the GRASP code. Collision strengths are also calculated over a wide energy range using the fully relativistic DARC code. Resonances are resolved in a fine energy mesh in the thresholds region and effective collision strengths are calculated for all 276 transitions at temperatures up to 107.7 K. Comparisons are made with the earlier available as well as other parallel calculations from the FAC code, and discrepancies are noted for some of the transitions in both ions.
    Journal of Physics Conference Series 11/2012; 388(6):2013-.
  • K. M. Aggarwal, F. P. Keenan
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    ABSTRACT: Energy levels and radiative rates for E1, E2, M1, and M2 transitions among the lowest 49 levels, belonging to the n <= 5 configurations of Ti XXI, are calculated using the GRASP code. Collision strengths are also calculated over a wide energy range using the fully relativistic DARC code. Resonances are resolved in a fine energy mesh in the thresholds region and effective collision strengths are calculated for all 1176 transitions at temperatures up to 107.5 K. Comparisons are made with the earlier available as well as other parallel calculations from the FAC code, and discrepancies are noted for some of the transitions, particularly the forbidden ones.
    Journal of Physics Conference Series 11/2012; 388(6):2014-.
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    K. M. Aggarwal, F. P. Keenan
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    ABSTRACT: We report calculations of energy levels, radiative rates and electron impact excitation cross sections and rates for transitions in He-like Kr XXXV. The GRASP (general-purpose relativistic atomic structure package) is adopted for calculating energy levels and radiative rates. For determining the collision strengths and subsequently the excitation rates, the Dirac Atomic R-matrix Code (DARC) is used. Oscillator strengths, radiative rates and line strengths are reported for all E1, E2, M1, and M2 transitions among the lowest 49 levels. Additionally, theoretical lifetimes are listed for all 49 levels. Collision strengths are averaged over a Maxwellian velocity distribution and the effective collision strengths obtained listed over a wide temperature range up to 10**8.1 K. Comparisons are made with similar data obtained with the Flexible Atomic Code (FAC) to assess the accuracy of the results and to highlight the importance of resonances, included in calculations with DARC, in the determination of effective collision strengths. Differences between the collision strengths from DARC and FAC, particularly for forbidden transitions, are also discussed. Finally, discrepancies between the present results of effective collision strengths from the {\sc darc} code and earlier semi-relativistic $R$-matrix data are noted over a wide range of electron temperatures for many transitions of Kr XXXV.
    Physica Scripta 07/2012; 86(3). · 1.03 Impact Factor
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    K. M. Aggarwal, F. P. Keenan
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    ABSTRACT: We report calculations of energy levels, radiative rates, and electron impact excitation rates for transitions in Li-like ions with 12 <= Z <= 20. The GRASP (general-purpose relativistic atomic structure package) is adopted for calculating energy levels and radiative rates, while for determining the collision strengths and subsequently the excitation rates, the Dirac atomic R-matrix code DARC is used. Oscillator strengths, radiative rates, and line strengths are reported for all E1, E2, M1, and M2 transitions among the lowest 24 levels of the Li-like ions considered. Collision strengths have been averaged over a Maxwellian velocity distribution, and the effective collision strengths obtained are reported over a wide temperature range up to 10$^{7.4}$ K. Additionally, lifetimes are also listed for all calculated levels of the above ions. Finally, extensive comparisons are made with available results in the literature, as well as with our parallel calculations for all parameters with the Flexible Atomic Code FAC in order to assess the accuracy of the reported results.
    Atomic Data and Nuclear Data Tables 07/2012; 99(2). · 1.00 Impact Factor
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    ABSTRACT: The VUV/XUV spectral region is particularly rich in lines emitted by plasmas with temperatures <= 30 keV used in fusion research. Examples are presented of analyses of JET tokamak data involving C VUV/XUV radiation. In the first, the C IV divertor emission is modelled, with agreement between theory and experiment to within the measurement accuracy of ~+/-10%. A second deals with C emission from the Scrape-off Layer (SOL) within the main chamber for which inconsistencies are found.
    05/2012;
  • Kanti M. Aggarwal, F. P. Keenan
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    ABSTRACT: Emission lines of Ti XIX are important for the modeling and diagnostics of lasing, fusion and astrophysical plasmas, for which atomic data are required for a variety of parameters, such as energy levels, radiative rates (A- values), and excitation rates or equivalently the effective collision strengths (Υ), which are obtained from the electron impact collision strengths (Ω). Experimentally, energy levels are available for Ti XIX on the NIST website, but there is paucity for accurate collisional atomic data. Therefore, here we report a complete set of results (namely energy levels, radiative rates, and effective collision strengths) for all transitions among the lowest 98 levels of Ti XIX. These levels belong to the (1s2) 2s2, 2s2p, 2p2, 2s3l, 2p3l, 2s4l, and 2p4l configurations. Finally, we also report the A- values for four types of transitions, namely electric dipole (E1), electric quadrupole (E2), magnetic dipole (M1), and magnetic quadrupole (M2), because these are also required for plasma modeling. For our calculations of wavefunctions, we have adopted the fully relativistic GRASP code, and for the calculations of Ω, the Dirac atomic R-matrix code (DARC) of PH Norrington and IP Grant. Additionally, parallel calculations have also been performed with the Flexible Atomic Code (FAC) of Gu, so that all atomic parameters can be rigorously assessed for accuracy.
    05/2012;
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    Kanti M Aggarwal, Francis P Keenan
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    ABSTRACT: We report calculations of energy levels, radiative rates and electron impact excitation cross sections and rates for transitions in He-like Mg XI, Al XII, P XIV and S XV. The GRASP (general-purpose relativistic atomic structure package) code is adopted to calculate energy levels and radiative rates. To determine the collision strengths and subsequently the excitation rates, the Dirac atomic R-matrix code (DARC) is used. Oscillator strengths, radiative rates and line strengths are reported for all E1, E2, M1 and M2 transitions among the lowest 49 levels of each ion. Collision strengths are averaged over a Maxwellian velocity distribution and the effective collision strengths obtained are listed over a wide temperature range up to 107.2 K. Comparisons are made with similar data obtained from the flexible atomic code (FAC) to highlight the importance of resonances, included in calculations with DARC, in the determination of effective collision strengths. Discrepancies between the collision strengths from DARC and FAC, particularly for forbidden transitions, are also discussed. Additionally, theoretical lifetimes are listed for all the 49 levels of the above four ions.
    Physica Scripta 01/2012; 85(2). · 1.03 Impact Factor
  • Kanti M Aggarwal, Francis P Keenan
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    ABSTRACT: We report calculations of energy levels, radiative rates and electron impact excitation cross sections and rates for transitions in He-like Cl XVI, K XVIII, Ca XIX and Sc XX. The GRASP (general-purpose relativistic atomic structure package) is adopted for calculating energy levels and radiative rates. To determine the collision strengths and subsequently the excitation rates, the Dirac atomic R-matrix code (DARC) is used. Oscillator strengths, radiative rates and line strengths are reported for all E1, E2, M1 and M2 transitions among the lowest 49 levels of each ion. Collision strengths are averaged over a Maxwellian velocity distribution and the effective collision strengths obtained listed over a wide temperature range up to 107.4 K. Comparisons are made with similar data obtained from the flexible atomic code (FAC) to highlight the importance of resonances, included in calculations with DARC, in the determination of effective collision strengths. Discrepancies between the collision strengths from DARC and FAC, particularly for forbidden transitions, are also discussed. Additionally, theoretical lifetimes are listed for all the 49 levels of the above four ions.
    Physica Scripta 01/2012; 85(2). · 1.03 Impact Factor
  • Kanti M Aggarwal, Francis P Keenan
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    ABSTRACT: We report calculations of energy levels, radiative rates and electron impact excitation cross sections and rates for transitions in He-like Ti XXI, V XXII, Cr XXIII and Mn XXIV. grasp (general-purpose relativistic atomic structure package) is adopted for calculating energy levels and radiative rates. For determining the collision strengths and subsequently the excitation rates, the Dirac atomic R-matrix code (darc) is used. Oscillator strengths, radiative rates and line strengths are reported for all E1, E2, M1 and M2 transitions among the lowest 49 levels of each ion. Additionally, theoretical lifetimes are listed for all the 49 levels of the above four ions. Collision strengths are averaged over a Maxwellian velocity distribution and the effective collision strengths obtained listed over a wide temperature range up to 107.5 K. Comparisons are made with similar data obtained using the flexible atomic code (fac) to highlight the importance of resonances, included in calculations with darc, in the determination of effective collision strengths. Discrepancies between the collision strengths from darc and fac, in particular for forbidden transitions, are also discussed. Finally, discrepancies between the present results for effective collision strengths with the darc code and earlier semi-relativistic R-matrix data are noted over a wide range of electron temperatures for many transitions in all ions.
    Physica Scripta 01/2012; 85(6). · 1.03 Impact Factor

Publication Stats

843 Citations
610.39 Total Impact Points

Institutions

  • 1982–2014
    • Queen's University Belfast
      • • Astrophysics Research Centre (ARC)
      • • Department of Physics and Astronomy
      • • Department of Applied Mathematics & Theoretical Physics
      Béal Feirste, N Ireland, United Kingdom
  • 2008
    • The Catholic University of America
      • Department of Physics
      Washington, D. C., DC, United States
  • 1979–2006
    • University of Delhi
      • Department of Physics & Astrophysics
      Delhi, NCT, India
  • 1998
    • University of Malaya
      Kuala Lumpor, Kuala Lumpur, Malaysia
  • 1992
    • Louisiana State University
      • Department of Physics & Astronomy
      Baton Rouge, Louisiana, United States