• Volume 64, Issue 1

      January 2005,   pages  1-158

    • Failure of Kak quantum key distribution protocol

      Ching-Nung Yang Su-Hsuan Chu Bing-Ling Lu

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      Kak’s quantum key distribution (QKD) protocol provides not only the distribution but also the integrity of secret key simultaneously in quantum channel. Consequently the additional exchange of information, used to check whether an eavesdropper exists, is unnecessary. In this comment, we will point out the failure of Kak’s protocol and show that Kak’s protocol does not have the joint distribution and integration that the author declares in [1].

    • A relativistic core-envelope model on pseudospheroidal space-time

      Ramesh Tikekar V O Thomas

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      A core-envelope model for superdense matter distribution with the feature- core consisting of anisotropic fluid distribution and envelope with isotropic fluid distribution is reported on the background of pseudospheroidal space-time. The physical plausibility of the model is examined analytically and numerically.

    • Mean square number fluctuation for a fermion source and its dependence on neutrino mass for the universal cosmic neutrino background

      Swapnil S Jawkar Sudhanshu S Jha

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      Using the general formulation for obtaining chemical potentialμ of an ideal Fermi gas of particles at temperature T, with particle rest mass m0 and average density 〈N〉/V, the dependence of the mean square number fluctuation 〈ΔN2〉/V on the particle mass m0 has been calculated explicitly. The numerical calculations are exact in all cases whether rest mass energym0c2 is very large (non-relativistic case), very small (ultra-relativistic case) or of the same order as the thermal energy kBT. Application of our results to the detection of the universal very low energy cosmic neutrino background (CNB), from any of the three species of neutrinos, shows that it is possible to estimate the neutrino mass of these species if from approximate experimental measurements of their momentum distribution one can extract, someday, not only the density 〈Nv〉/V but also the mean square fluctuation 〈Δv2〉/V. If at the present epoch, the universe is expanding much faster than thermalization rate for CNB, it is shown that our analysis leads to a scaled neutrino massmv instead of the actual massm0v.

    • Nuclear matter equation of state and σ-meson parameters

      A B Santra U Lombardo

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      We try to determine phenomenologically the extent of in-medium modification of σ-meson parameters so that the saturation observables of the nuclear matter equation of state (EOS) are reproduced. To calculate the EOS we have used Brueckner-Bethe-Goldstone formalism with Bonn potential as two-body interaction. We find that it is possible to understand all the saturation observables, namely, saturation density, energy per nucleon and incompressibility, by incorporating in-medium modification of σ-meson-nucleon coupling constant and σ-meson mass by a few per cent.

    • Cluster emission in superdeformed Sr isotopes in the ground state and formed in heavy-ion reaction

      K P Santhosh Antony Joseph

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      Cluster decay of superdeformed76, 78, 80Sr isotopes in their ground state are studied taking the Coulomb and proximity potential as the interacting barrier for the post-scission region. The predictedT1/2 values are found to be in close agreement with those values reported by the preformed cluster model (PCM). Our calculation shows that these nuclei are stable against both light and heavy cluster emissions. We studied the decay of these nuclei produced as an excited compound system in heavy-ion reaction. It is found that inclusion of excitation energy increases the decay rate (decreasesT1/2 value) considerably and these nuclei become unstable against decay. These findings support earlier observation of Guptaet al based on PCM.

    • Adiabatic heavy-ion fusion potentials for fusion at deep sub-barrier energies

      S V S Sastry S Kailas A K Mohanty A Saxena

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      The recently reported unusual behaviour of fusion cross-sections at extreme sub-barrier energies has been examined. The adiabatic limit of fusion barriers has been determined from experimental data using the barrier penetration model. These adiabatic barriers are consistent with the adiabatic fusion barriers derived from the modified Wilzynska-Wilzynski prescription. The fusion barrier systematics has been obtained for a wide range of heavy-ion systems.

    • Scaling of triple differential cross-sections for asymmetric (e, 2e) process on helium isoelectronic ions by fast electrons

      M K Srivastava

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      A simple scaling law is obtained for asymmetric (e, 2e) process on helium isoelectronic ions by fast electrons. It is based on treating the targets as having one active electron moving in the effective Coulomb field of the atomic core with an effective chargeZ′ = Z- 5/8. This effective charge is also used in the description of the scattered and ejected electrons. The model has been tested against other available (e, 2e) results on helium in asymmetric geometry. The scaling law is found to work reasonably well for fast incident electrons and becomes increasingly accurate as targetZ increases.

    • Singly-resonant optical parametric oscillator based on KTA crystal

      S Das S Gangopadhyay C Ghosh G C Bhar

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      Tunable mid-infra-red radiation by singly resonant optical parametric oscillation based on KTA crystal pumped by multi-axial Gaussian shape beam from Q-switched Nd:YAG laser has been demonstrated. Threshold energy of oscillation at different idler wavelengths for different cavity length has been demonstrated. Single pass conversion efficiency of incident pump energy to infra-red wavelength has also been measured.

    • Bifurcation and chaos in simple jerk dynamical systems

      Vinod Patidar K K Sud

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      In recent years, it is observed that the third-order explicit autonomous differential equation, named as jerk equation, represents an interesting sub-class of dynamical systems that can exhibit many major features of the regular and chaotic motion. In this paper, we investigate the global dynamics of a special family of jerk systems {ie075-01}, whereG(x) is a non-linear function, which are known to exhibit chaotic behaviour at some parameter values. We particularly identify the regions of parameter space with different asymptotic dynamics using some analytical methods as well as extensive Lyapunov spectra calculation in complete parameter space. We also investigate the effect of weakening as well as strengthening of the non-linearity in theG(x) function on the global dynamics of these jerk dynamical systems. As a result, we reach to an important conclusion for these jerk dynamical systems that a certain amount of non-linearity is sufficient for exhibiting chaotic behaviour but increasing the non-linearity does not lead to larger regions of parameter space exhibiting chaos.

    • Investigation of multipactor breakdown in communication satellite microwave co-axial systems

      S K Nagesh D Revannasiddiah S V K Shastry

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      Multipactor breakdown or multipactor discharge is a form of high frequency discharge that may occur in microwave components operating at very low pressures. Some RF components of multi-channel communication satellites have co-axial geometry and handle high RF power under near-vacuum conditions. The breakdown occurs due to secondary electron resonance, wherein electrons move back and forth in synchronism with the RF voltage across the gap between the inner and outer conductors of the co-axial structure. If the yield of secondary electrons from the walls of the co-axial structure is greater than unity, then the electron density increases with time and eventually leads to the breakdown. In this paper, the current due to the oscillating electrons in the co-axial geometry has been treated as a radially oriented Hertzian dipole. The electric field, due to this dipole, at any point in the coaxial structure, may then be determined by employing the dyadic Green’s function technique. This field has been compared with the field that would exist in the absence of multipactor.

    • Relaxation of femtosecond photoexcited electrons in a polar indirect band-gap semiconductor nanoparticle

      Navinder Singh

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      A model calculation is given for the energy relaxation of a non-equilibrium distribution of hot electrons (holes) prepared in the conduction (valence) band of a polar indirect band-gap semiconductor, which has been subjected to homogeneous photoexcitation by a femtosecond laser pulse. The model assumes that the pulsed photoexcitation creates two distinct but spatially interpenetrating electron and hole non-equilibrium subsystems that initially relax non-radiatively through the electron (hole)-phonon processes towards the conduction (valence) band minimum (maximum), and finally radiatively through the phonon-assisted electron-hole recombination across the band-gap, which is a relatively slow process. This leads to an accumulation of electrons (holes) at the conduction (valence) band minimum (maximum). The resulting peaking of the carrier density and the entire evolution of the hot electron (hole) distribution has been calculated. The latter may be time resolved by a pump-probe study. The model is particularly applicable to a divided (nanometric) polar indirect band-gap semiconductor with a low carrier concentration and strong electron-phonon coupling, where the usual two-temperature model [1-4] may not be appropriate.

    • Electronic and vibrational Raman spectroscopy of Nd0.5Sr0.5MnO3 through the phase transitions

      Md Motin Seikh A K Sood Chandrabhas Narayana

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      Raman scattering experiments have been carried out on single crystals of Nd0.5Sr0.5MnO3 as a function of temperature in the range of 320–50 K, covering the paramagnetic insulator-ferromagnetic metal transition at 250 K and the charge-ordering antiferromagnetic transition at 150 K. The diffusive electronic Raman scattering response is seen in the paramagnetic phase which continue to exist even in the ferromagnetic phase, eventually disappearing below 150 K. We understand the existence of diffusive response in the ferromagnetic phase to the coexistence of the different electronic phases. The frequency and linewidth of the phonons across the transitions show significant changes, which cannot be accounted for only by anharmonic interactions.

    • Collisional excitation of neon-like Ni XIX using the Breit-PauliR-matrix method

      Narendra Singh Man Mohan

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      Collision strength for the transition within the first five fine-structure levels in Ni XIX are calculated using the Breit-PauliR-matrix method. Configuration interaction wave functions are used to represent the target states included in theR-matrix expansion. The relativistic effects are incorporated in the Breit-Pauli approximation by including the one-body mass correction, Darwin and spin-orbit interaction terms in scattering equations.

    • Novel approach for prediction of ultrasonic velocity in quaternary liquid mixtures

      J D Pandey A K Singh Ranjan Dey

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      A modified Flory theory along with the Auerbach and Altenberg relations has been employed for the computation of ultrasonic velocity of three quaternary liquid mixtures and a comparative study of all the three relations has then been carried out.

    • Effect of dielectronic recombination on the charge-state distribution and soft X-ray line intensity of laser-produced carbon plasma

      A Chowdhury G P Gupta P A Naik P D Gupta

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      The effect of dielectronic recombination in determining charge-state distribution and radiative emission from a laser-produced carbon plasma has been investigated in the collisional radiative ionization equilibrium. It is observed that the relative abundances of different ions in the plasma, and soft X-ray emission intensity get significantly altered when dielectronic recombination is included. Theoretical estimates of the relative population of CVI to CV ions and ratio of line intensity emitted from them for two representative formulations of dielectronic recombination are presented.

    • Theoretical study of 2 X 2 element planar array of equilateral triangular patch microstrip antenna in plasma medium

      K K Verma K R Soni

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      The radiation properties of 2 X 2 element planar array of equilateral triangular patch microstrip antenna in plasma medium are studied. The array factor and far-zone EM-mode and P-mode radiation fields of the array geometry are derived using vector wave function techniques and pattern multiplication approaches. The total field patterns and various characteristics of pattern such as half power beam width (HPBW), first null beam width (FNBW) and direction of maximum radiation are computed for two different values of progressive phase excitation difference between the elements. The results of this array geometry are obtained both in plasma medium and in free space and compared with those of single element equilateral triangular patch microstrip antenna.

    • Total energy, equation of state and bulk modulus of AlP, AlAs and AlSb semiconductors

      A R Jivani H J Trivedi P N Gajjar A R Jani

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      Recently proposed model potential which combines both linear and quadratic types of interactions is employed for the investigation of some properties like the total energy, equation of state and bulk modulus of AlP, AlAs and AlSb semiconductor compounds using higher-order perturbation theory. The model potential parameter is determined using zero pressure condition. The ratio of the covalent bonding termEcov to the secondorder termE2 is 6.77% to 11.85% which shows that contribution from higher order terms are important for zinc-blende-type crystals. The calculated numerical results of the total energy, energy band gap at Jones-zone face and bulk modulus of these compounds are in good agreement with the experimental data and found much better than other such theoretical findings. We have also studied pressure-volume relations of these compounds. The present study is carried out using six different screening functions along with latest screening function proposed by Sarkaret al. It is found from the present study that effect of exchange and correlation is clearly distinguishable.

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