• Amita

      Articles written in Pramana – Journal of Physics

    • Magnetic rotation and chiral symmetry breaking

      Ashok Kumar Jain Amita

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      The deformed mean field of nuclei exhibits various geometrical and dynamical symmetries which manifest themselves as various types of rotational and decay patterns. Most of the symmetry operations considered so far have been defined for a situation wherein the angular momentum coincides with one of the principal axes and the principal axis cranking may be invoked. New possibilities arise with the observation of rotational features in weakly deformed nuclei and now interpreted as magnetic rotational bands. More than 120 MR bands have now been identified by filtering the existing data. We present a brief overview of these bands. The total angular momentum vector in such bands is tilted away from the principal axes. Such a situation gives rise to several new possibilities including breaking of chiral symmetry as discussed recently by Frauendorf. We present the outcome of such symmetries and their possible experimental verification. Some possible examples of chiral bands are presented.

    • Synthetic magnetic opals

      Amita Gupta Alexei Yu Ganin Parmanand Sharma Vikrant Agnihotri LM Belova KV Rao Mikhail E Kozlov AA Zakhidov RH Baughman

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      We present studies of novel nanocomposites of BiNi impregnated into the structure of opals as well as inverse opals. Atomic force microscopy and high resolution elemental analyses show a highly ordered structure and uniform distribution of the BiNi filler in the matrix. These BiNi-based nanocomposites are found to exhibit distinct ferromagnetic-like ordering with transition temperature of about 675 K. As far as we know there exists no report in literature on any BiNi compound which is magnetic.

    • A microscopic study of deformation systematics in 154−166Dy isotopes

      Amita Dua Arun Bharti S K Khosa

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      The Hartree–Bogoliubov (HB) framework of calculations has been applied for calculating various nuclear structure quantities for 154−166Dy mass chains. In this framework, the intrinsic quadrupole moments, the low-lying yrast states ($E_{2}^{+}$ and $E_{4}^{+}$) and occupation numbers for various shell model orbits have been obtained. The calculated results indicate that the observed onset of deformation in going from 154Dy to 166Dy arises due to enhanced occupation of $(h_{11/2})_{\pi}$ orbit, increased polarization of $(d_{5/2})_{\pi}$ orbit and increase in the occupation of down-slopping $`k'$ components of $(i_{13/2})_{v} and $(h_{9/2})_{υ}$ orbits.

    • Effect of solar features and interplanetary parameters on geomagnetosphere during solar cycle-23

      Santosh Kumar Amita Raizada

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      The dependence of geomagnetic activity on solar features and interplanetary (IP) parameters is investigated. Sixty-seven intense (−200 nT $\leq$ Dst < −100 nT) and seventeen superintense (Dst < −200 nT) geomagnetic storms (GMSs) have been studied from January 1996 to April 2006. The number of intense and superintense GMSs show three distinct peaks during the 11-year period of 23rd solar cycle. The largest number of high strength GMSs are observed during maximum phase of solar cycle. Halo and partial halo CMEs are likely to be the major cause for these GMSs of high intensity. No relationship is observed between storm duration and the number of CMEs involved in its occurrence. The intensity of the GMS is also independent of the number of CMEs causing the occurrence of storm. These geoeffective CMEs show western and northern bias. Majority of the geoeffective CMEs are associated with X-ray solar flares (SFs). Solar and IP parameters, e.g., $V_{\text{CME}}$, $V_{\text{SW}}$, 𝐵, $B_{z}$ (GSE and GSM coordinates) and their products, e.g., $V_{\text{SW}}·B$ and $V_{\text{SW}}·B_{z}$ are observed and correlated to predict the occurrence of intense GMSs. V CME does not seem to be the appropriate parameter with the correlation coefficient, $r = −0.2$ with Dst index, whereas the correlation coefficient, $r = −0.57$, −0.65, 0.75, −0.68 and 0.77 of the parameters $V_{\text{SW}}$, 𝐵, $B_{z}$, $V_{\text{SW}}·B$ and $V_{\text{SW}}·B_{\text{z}}$ respectively, with Dst indicating that $V_{\text{SW}}·B_{\text{z}}$ and $B_{\text{z}}$ may be treated as the significant contributors in determining the strength of GMSs.

    • Collisionless stopping of electron current in an inhomogeneous electron magnetohydrodynamics plasma

      Amita Das Sharad K Yadav Predhiman Kaw Sudip Sengupta

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      A brief review of a recent work on a novel collisionless scheme for stopping electron current pulse in plasma is presented. This scheme relies on the inhomogeneity of the plasma medium. This mechanism can be used for heating an overdense regime of plasma where lasers cannot penetrate. The method can ensure efficient localized heating at a desired location. The suitability of the scheme to the frontline fast ignition laser fusion experiment has been illustrated.

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