• Volume 71, Issue 6

December 2008

• Møller's energy in the dyadosphere of a charged black hole

We use the Møller energy–momentum complex both in general relativity and teleparallel gravity to evaluate energy distribution (due to matter plus fields including gravity) in the dyadosphere region for Reissner–Nordström black hole. We found the same and acceptable energy distribution in these different approaches of the Møller energy–momentum complex. Our teleparallel gravitational result is also independent of the teleparallel dimensionless coupling constant, which means that it is valid in any teleparallel model. This paper sustains (a) the importance of the energy–momentum definitions in the evaluation of the energy distribution of a given space–time and (b) the viewpoint of Lessner that the Møller energy–momentum complex is a powerful concept for energy and momentum.

• 110° C thermoluminescence glow peak of quartz – A brief review

The 110°C glow peak of quartz, though unstable at room temperature, has worked wonderfully in archaeology and retrospective dosimetry due to its pre-dose sensitization property. Various aspects of the peak, like its nature, defect centres involved, the impact of different stimuli and its application have been extensively studied. The main aims of this review are to (i) summarize briefly the work carried out on the various facets of this TL glow peak during the last four decades and (ii) identify the areas which need further attention in order to have a better understanding of the luminescence characteristics of this TL peak.

• Exact solutions to the generalized Lienard equation and its applications

Some new exact solutions of the generalized Lienard equation are obtained, and the solutions of the equation are applied to solve nonlinear wave equations with nonlinear terms of any order directly. The generalized one-dimensional Klein–Gordon equation, the generalized Ablowitz (A) equation and the generalized Gerdjikov–Ivanov (GI) equation are investigated and abundant new exact travelling wave solutions are obtained that include solitary wave solutions and triangular periodic wave solutions.

• Anisotropic Bianchi-I universe with phantom field and cosmological constant

We study an anisotropic Bianchi-I universe in the presence of a phantom field and a cosmological constant. Cosmological solutions are obtained when the kinetic energy of the phantom field is of the order of anisotropy and dominates over the potential energy of the field. The anisotropy of the universe decreases and the universe transits to an isotropic flat FRW universe accommodating the present acceleration. A class of new cosmological solutions is obtained for an anisotropic universe in case an initial anisotropy exists which is bigger than the value determined by the parameter of the kinetic part of the field. Later, an autonomous system of equations for an axially symmetric Bianchi-I universe with phantom field in an exponential potential is studied. We discuss the stability of the cosmological solutions.

• Performance characteristics of positive and negative delayed feedback on chaotic dynamics of directly modulated InGaAsP semiconductor lasers

The chaotic dynamics of directly modulated semiconductor lasers with delayed optoelectronic feedback is studied numerically. The effects of positive and negative delayed optoelectronic feedback in producing chaotic outputs from such lasers with nonlinear gain reduction in its optimum value range is investigated using bifurcation diagrams. The results are confirmed by calculating the Lyapunov exponents. A negative delayed optoelectronic feedback configuration is found to be more effective in inducing chaotic dynamics to such systems with nonlinear gain reduction factor in the practical value range.

• Electric dipolarizability of 7Li

We calculate the electric dipolarizability of 7Li nucleus within the cluster model and estimate a value of about 0.0188 fm3. We also discuss the possibility of observing this in the scattering of 7Li from a 208Pb target at energies about 30 MeV.

• RF properties of 700 MHz, $\beta = 0.42$ elliptical cavity for high current proton acceleration

BARC is developing a technology for the accelerator-driven subcritical system (ADSS) that will be mainly utilized for the transmutation of nuclear waste and enrichment of U233. Design and development of superconducting medium velocity cavity has been taken up as a part of the accelerator-driven subcritical system project. We have studied RF properties of 700 MHz, $\beta = 0.42$ single cell elliptical cavity for possible use in high current proton acceleration. The cavity shape optimization studies have been done using SUPERFISH code. A calculation has been done to find out the velocity range over which this cavity can accelerate protons efficiently and to select the number of cells/cavity. The cavity's peak electric and magnetic fields, power dissipation $P_{c}$, quality factor 𝑄 and effective shunt impedance $ZT^{2}$ were calculated for various cavity dimensions using these codes. Based on these analyses a list of design parameters for the inner cell of the cavity has been suggested for possible use in high current proton accelerator.

• Vibrational spectra and normal coordinate analysis on structure of chlorambucil and thioguanine

A normal coordinate analysis on chlorambucil and thioguanine has been carried out with a set of symmetry coordinates following Wilson's $F –G$ matrix method. The potential constants evaluated for these molecules are found to be in good agreement with literature values thereby confirming the vibrational assignments. To check whether the chosen set of vibrational frequencies contribute maximum to the potential energy associated with the normal coordinates of the molecule, the potential energy distribution has been evaluated.

• Development of a 2 MW relativistic backward wave oscillator

In this paper, a high power relativistic backward wave oscillator (BWO) experiment is reported. A 230 keV, 2 kA, 150 ns relativistic electron beam is generated using a Marx generator. The beam is then injected into a hollow rippled wall metallic cylindrical tube that forms a slow wave structure. The beam is guided using an axial pulsed magnetic field having a peak value 1 T and duration 1 ms. The field is generated by the discharge of a capacitor bank into a solenoidal coil. A synchronization circuit ensures the generation of the electron beam at the instant when the axial magnetic field attains its peak value. The beam interacts with the SWS modes and generates microwaves due to Cherenkov interaction. Estimated power of 2 MW in TM 01 mode is observed.

• Revisiting non-degenerate parametric down-conversion

The quantum dynamics of a two-mode non-resonant parametric down-conversion process is studied by recasting the time evolution equations for the basic operators in an equivalent spin equation form with simpler exact solutions for a pump field with harmonic time dependence. Expectation values of suitable operators for studying important features such as squeezing and quantum revivals are presented in simple forms.

• Design, construction and characterization of the compact ultrafast terahertz free-electron laser undulator

A compact ultrafast terahertz (CUTE) free-electron laser (FEL) is being developed at the Raja Ramanna Centre for Advanced Technology (RRCAT), Indore. The undulator required for the CUTE-FEL has recently been developed. We have designed, built and characterized a variable gap, 5 cm period, 2.5 m long pure permanent magnet undulator in two identical segments. The tolerable error in the magnetic field was 1% in rms, and we have measured it to be 0.7%. The obtained rms phase shake is around 2°. To ensure that the trajectories do not have an exit error in position or angle, corrector coils have been designed. Shimming coils have been applied for both the undulator segments to reduce the amplitude of the betatron oscillations in the vertical trajectory. Details of novel corrector coils and soft iron shims are given and their performance is discussed.

• Magnetic field dependence of vortex activation energy: A comparison between MgB2, NbSe2 and Bi2Sr2Ca2Cu3O10 superconductors

The dissipative mechanism at low current density is compared in three different classes of superconductors. This is achieved by measuring the resistance as a function of temperature and magnetic field in clean polycrystalline samples of NbSe2, MgB2 and Bi2Sr2Ca2Cu3O10 (BSCCO) superconductors. Thermally activated flux flow behaviour is seen in all the three systems and clearly identified in bulk MgB2. While the activation energy at low fields for MgB2 is comparable to Bi2Sr2Ca2Cu3O10, its field dependence follows a parabolic behaviour unlike a power-law dependence seen in Bi2Sr2Ca2Cu3O10. We analyse our results based on Kramer's scaling for grain boundary pinning in MgB2 and NbSe2.

• Coded nanoscale self-assembly

We demonstrate coded self-assembly in nanostructures using the code seeded at the component level through computer simulations. Defects or cavities occur in all natural assembly processes including crystallization and our simulations capture this essential aspect under surface minimization constraints for self-assembly. Our bottom-up approach to nanostructures would provide a new dimension towards nanofabrication and better understanding of defects and crystallization process.

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

The dependence of geomagnetic activity on solar features and interplanetary (IP) parameters is investigated. Sixty-seven intense (−200 nT $\leq$ Dst &lt; −100 nT) and seventeen superintense (Dst &lt; −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.

• Energy-Momentum Localization in Marder Space-Time

• Subject Index

• Author Index

• Pramana – Journal of Physics

Current Issue
Volume 93 | Issue 6
December 2019

• Editorial Note on Continuous Article Publication

Posted on July 25, 2019