• Volume 27, Issue 1-2

      July 1986,   pages  1-361

    • The three faces of Maxwell’s equations

      N Mukunda E C G Sudarshan

      More Details Abstract Fulltext PDF

      In dealing with electromagnetic phenomena and in particular the phenomena of optics, despite the recognition of the quanta of light people tend to talk of the amplitudes and field strengths, as if the electromagnetic field were a classical field. For example we measure the wavelength of light by studying interference fringes. In this paper we study the interrelationship of three ways of looking at the problem: in terms of classical wave fields, wave function of the photon; and the quantized wave field. The comparison and contrasts of these three modes of description are carefully analyzed in this paper. The ways in which these different modes complement our intuition and insight are also discussed.

    • An age-dependent model of cavity radiation and its detection

      S K Srinivasan

      More Details Abstract Fulltext PDF

      Cavity radiation is modelled as a population point process with age-dependent birth rate. A method of phases is introduced to analyze special types of age dependencies. The conditional life-time of the cavity photon is assumed to be in hypothetical phases, the life-span of the phases being distributed independently and exponentially. The analysis leads to an explicit differential equation for the generating function of the population size. The detection process is analyzed and an explicit expression for the correlation of the counts provided. By an appropriate choice of the parameters, the spectrum corresponding to Gaussian Lorentzian light is recovered.

    • Quantum-ohmic resistance fluctuation in disordered conductors—An invariant imbedding approach

      N Kumar

      More Details Abstract Fulltext PDF

      It is now well known that in the extreme quantum limit, dominated by the elastic impurity scattering and the concomitant quantum interference, the zero-temperature d.c. resistance of a strictly one-dimensional disordered system is non-additive and non-self-averaging. While these statistical fluctuations may persist in the case of a physically thin wire, they are implicitly and questionably ignored in higher dimensions. In this work, we have re-examined this question. Following an invariant imbedding formulation, we first derive a stochastic differential equation for the complex amplitude reflection coefficient and hence obtain a Fokker-Planck equation for the full probability distribution of resistance for a one-dimensional continuum with a gaussian white-noise random potential. We then employ the Migdal-Kadanoff type bond moving procedure and derive thed-dimensional generalization of the above probability distribution, or rather the associated cumulant function—‘the free energy’. Ford=3, our analysis shows that the dispersion dominates the mobility edge phenomena in that (i) a one-parameterβ-function depending on the mean conductance only does not exist, (ii) one has a line of fixed-points in the space of the first two cumulants of conductance, (iii) an approximate treatment gives a diffusion-correction involving the second cumulant. It is, however, not clear whether the fluctuations can render the transition at the mobility edge ‘first-order’. We also report some analytical results for the case of the one-dimensional system in the presence of a finite electric field. We find a cross-over from the exponential to the power-law length dependence of resistance as the field increases from zero. Also, the distribution of resistance saturates asymptotically to a Poissonian form. Most of our analytical results are supported by the recent numerical simulation work reported by some authors.

    • Effect of polymerization and depolymerization reactions on molecular size distribution in living polymers

      F C Auluck G C Gupta V S Nanda

      More Details Abstract Fulltext PDF

      In this paper we have derived an exact expression for the molecular size distribution in living polymers for batch polymerization when depropagation is simultaneously operative. This expression is valid at a point of time when inhomogeneity is slightly greater than half that of the final equilibrium distribution.

    • Electron transport in rectangular quantum wells

      B R Nag

      More Details Abstract Fulltext PDF

      Experimental results on low-field and high-field electron transport in rectangular quantum wells are reviewed. The related theory is presented and the experimental results are examined in the light of the theory. It is concluded that although some experimental results are available and the theory of transport has been developed, numerical agreement between theory and experiments has not yet been reached.

    • Gravitational fields with space-times of Bianchi type IX

      P C Vaidya L K Patel

      More Details Abstract Fulltext PDF

      Spatially homogeneous space-times of Bianchi type IX are considered. A general scheme for the derivation of exact solutions of Einstein’s equations corresponding to perfect fluid plus pure radiation fields is outlined. Some simple rotating Bianchi type IX cosmological models are presented. The details of these solutions are also discussed.

    • Duality in physical sciences and beyond

      A N Mitra

      More Details Abstract Fulltext PDF

      An extended meaning of duality is suggested in the context of development of major themes in physical sciences since Newton. In such a generalization,five distinct aspects of duality are sought to be identified and illustrated through concrete examples drawn from various physical concepts, old and new. These are (i) reciprocity, (ii) parallelism, (iii) alternative formulation, (iv) unification and (v) measurement incompatibility. Bohr’s view of duality and the Copenhagen Interpretation are discussed briefly in this context. Finally, duality aspects beyond physics are briefly touched upon, the philosophical link being provided by Bohr’s Complementarity Principle on the one hand, and recent attempts (notably by Capra) to draw suggestive parallels between modern science and Eastern mysticism on the other.

    • Ionization states of cosmic rays:Anuradha (IONS) experiment in Spacelab-3

      S Biswas R Chakraborti R Cowsik N Durgaprasad P J Kajarekar R K Singh M N Vahia J S Yadav N Dutt J N Goswami D Lal H S Mazumdar D V Subhedar M K Padmanabhan

      More Details Abstract Fulltext PDF

      The measurements of the ionization states, composition, energy spectra and spatial distribution of heavy ions of helium to iron of energies 10–100 MeV/amu in the anomalous cosmic rays are of major importance in understanding their origin which is unknown at present.Anuradha (IONS) cosmic ray experiment in Spacelab-3 was designed to determine the above properties in near earth space and this had a highly successful flight and operations aboard the shuttle Challenger at an orbital altitude of 352 km during 29 April to 6 May 1985. The instrument employs solid state nuclear track detectors (CR-39) of high sensitivity and large collecting area of about 800 cm2 and determines the arrival time information of particles with active elements. Experimental methods, flight operations and preliminary results are briefly described. Initial results indicate that relatively high fluxes of low energy cosmic ray α-particles, oxygen group and heavier ions were obtained. The flight period corresponded to that of quiet Sun and the level of solar activity was close to solar minimum. It is estimated that about 10,000 events of low energy cosmic ray alpha particles with time annotation are recorded in the detector together with similar number of events of oxygen and heavier ions of low energy cosmic rays.

    • Boson-fermion relations in several dimensions

      K R Parthasarathy K B Sinha

      More Details Abstract Fulltext PDF

      Zero and positive temperature fermion field operators in several dimensions are constructed as stochastic integrals of certain reflection valued processes with respect to the corresponding boson field operator processes.

    • Supersymmetric classical mechanics

      S N Biswas S K Soni

      More Details Abstract Fulltext PDF

      The purpose of the paper is to construct a supersymmetric Lagrangian within the framework of classical mechanics which would be regarded as a candidate for passage to supersymmetric quantum mechanics.

    • The thorium cycle for fast breeder reactors

      R Ramanna S M Lee

      More Details Abstract Fulltext PDF

      The role that could be played by liquid metal-cooled fast breeder reactors (LMFBRs) in the utilization of India’s considerable thorium resources is reviewed in this article. Distinct advantages of thorium-based fuels over plutonium-uranium fuels in LMFBRs pertain to a more favourable coolant voiding reactivity coefficient and better fuel element irradiation stability. The poorer breeding capability of thorium-fuelled fast reactors can in principle be overcome by improved core design and development of advanced fuel concepts. The technical feasibility of such advanced thorium fuels and core designs must be established by sustained research and development. It is also necessary to efficiently close the thorium fuel cycle of fast breeder reactors by appropriate development of the fuel reprocessing and refabrication stages. The Fast Breeder Test Reactor (FBTR) at Kalpakkam is expected to be an important tool for development of thorium fuel and fuel cycle technology. A quick look at the economics of the thorium cycle for fast reactors, vis-a-vis the more conventional uranium cycle indicates only a small and acceptable cost disadvantage on account of the need for remote fabrication of recycled thorium fuel.

    • Proton-nucleus optical model potential at low energies—a review

      M K Mehta S Kailas

      More Details Abstract Fulltext PDF

      Ever since it was proposed more than three decades ago, the nuclear optical model has been very successful in interpreting a large body of nucleon-induced nuclear reaction data in terms of a complex nucleon-nucleus potential. Rapid progress both in the experimental measurements and the theoretical developments in the last two decades has led to a better understanding of this nucleon-nucleus optical potential. From the parameter-fitting phenomenological stage, the optical model has come a long way and it is now possible to calculate the nucleon-nucleus optical potential in a reasonable way starting from the fundamental nucleon-nucleon interaction. Excellent reviews on various aspects of the optical model exist in the literature for proton energies above 10 MeV. The present article is an attempt to review comprehensively the status of the proton-nucleus optical potential at low proton energies, below the Coulomb-barrier, for target nuclei with mass numbers lying between 40 and 130. The sets of phenomenological optical potential derived mostly from (p, n) reaction data are reviewed and their applicabilities discussed. The neutron-nucleus optical model is referred to wherever it is relevant. Microscopic calculations for one case is carried out and compared with the corresponding phenomenological values.

    • Photophysics of 9-aminoacridinium hydrochloride

      D D Pant G C Joshi H B Tripathi

      More Details Abstract Fulltext PDF

      The steady state and time domain spectroscopy of 9-aminoacridinium hydrochloride have been studied. 9-aminoacridine (I), 9-aminoacridinium (II) and the double protonated ion (III) follow Waterman’s principle with respect to their spectra and lifetimes. It is established that the excimer formation in (II) is from the ground state dimers which undergo either thermally-activated radiationless excimer conversion or a geometrical rearrangement in the excited state at room temperature. The quenching of monomer emission by dimers or foreign quenchers (KI) is found to be of transient nature as suggested by the continuum model.

    • Flat field spectrograph using convex holographic diffraction grating and concave mirror

      N C Das M V R K Murty

      More Details Abstract Fulltext PDF

      In this paper we have discussed the aberration properties and the design procedure of a spectrograph which uses a convex holographic grating as the dispersing element and a concave mirror as the focusing element. Both the concave mirror and the convex grating have common axis and they are concentric. The grating is constructed by recording the interference fringes on the convex surface which are formed by two convergent light beams incident from opposite sides of the axis. The illuminating source of the spectrograph is located on a plane perpendicular to the axis and passing through the common centre. It has been found that under certain conditions both positive and negative order spectra are perfectly focused on this plane. Aberration properties of the zero order image as well as the positive and the negative order spectral images have been studied by actual ray tracing. Using this system, design parameters of a medium-sized spectrograph having moderate dispersion and good resolution throughout theuv-visible region of the spectrum have been specified. The performance of the spectrograph has been evaluated by plotting spot diagram.

    • Optically selective coatings

      K L Chopra G B Reddy

      More Details Abstract Fulltext PDF

      The natural optical selectivity of a material exhibited in the form of its reflectance, transmittance, or emittance spectra can be modified and tailored to yield any desired profile by applying surface coatings in the form of multilayers of suitable materials, or composite materials having an appropriate graded composition. This paper reviews the modes of selectivity, design and modelling of some technologically important optically selective coatings.

    • Effect of random density irregularities on nonlinear evolution of Langmuir waves in interplanetary medium

      B Buti M Mohan S K Alurkar

      More Details Abstract Fulltext PDF

      The evolution of nonlinear Langmuir waves in the interplanetary medium is investigated by appropriately accounting for the random density irregularities of the medium. A pair of modified Zakharov equations, which describe these waves, is solved numerically as an initial value problem for large scale (≫ 102 km) initial pertubations. For an ion acoustic-Langmuir solitary wave, the random irregularities damp the Langmuir wave by way of scattering and let the ion density perturbation radiate away in a few days. However an initial solitary or shock-like Langmuir wave excites the ion density perturbations within a fraction of a second, and then itself gets damped. These effects will strongly decelerate the collapse of large scale Langmuir waves. The possibility of detecting these processes, by means of interplanetary scintillation, is discussed.

    • Double-diffusive magnetoconvection

      N Rudraiah

      More Details Abstract Fulltext PDF

      This review deals principally with the interaction between double-diffusive convection and an externally imposed vertical magnetic field in a Boussinesq fluid. Both linear and nonlinear (two and three-dimensional) theories have been discussed. Double-diffusive magnetoconvection is shown to exhibit a rich variety of dynamical behaviour unimaginable in a single component system and serves as a guide to the behaviour of all triple-diffusive systems. Finally, the effects of cross-diffusion, rotation and chemical reaction on double-diffusive magnetoconvection and pattern selection have been briefly touched upon.

    • Electron and x-ray diffraction studies on Al86Fe14, Al82Fe18 and Al75Fe25 quasicrystals

      J A Sekhar T Rajasekharan P Rama Rao G Parthasarathy S Ramkumar E S R Gopal C S Lakshmi R M Mallya

      More Details Abstract Fulltext PDF

      Electron and x-ray diffraction experiments on the metlt-spun Al100−xFex (x=14, 18, 25) alloys are carried out. It is observed that all the melt-spun alloys possessing the quasi-crystalline phases have icosahedral point-group symmetry.

    • Study of theKα satellites and hypersatellites in the x-ray and Auger spectra of neon

      Lakshmi Natarajan A V Tankhiwale C Mande

      More Details Abstract Fulltext PDF

      We report in this paper our calculations of the energies of the satellite and hypersatellite lines in the x-ray and Auger spectra of neon, using screened hydrogenic wavefunctions. Our calculations have enabled us to draw an energy level diagram for the neon atom in various defect-electron configurations. It is possible to show the transitions giving rise to the various x-ray and Auger satellites and hypersatellites using this diagram.

    • Effect of high pressure on the vibrational modes and the energy gap of ZnP2

      A Jayaraman R G Maines T Chattopadhyay

      More Details Abstract Fulltext PDF

      The pressure dependence of the vibrational modes in ZnP2 has been investigated by Raman Spectroscopy using a diamond anvil cell, up to 150 kbar pressure. The intrachain phosphorus modes exhibit a strong pressure dependence whereas the low frequency Zn-P modes soften very slightly under pressure. For a crystal which is treated as a molecular crystal this is an unexpected result. It is suggested that the behaviour may be due to a buckling of the phosphorus chain, or due to a double bond promotion between P atoms, or a charge transfer under pressure. The shift in the energy gap has also been measured to 100 kbar hydrostatic pressure. There is a small initial blue shift which gradually changes over to a red shift. However the whole shift in 100 kbar is quite small. Combining the (dEg/dP)T with the published (dEg/dT)P the thermal expansion contribution and the electron-phonon interaction contribution were evaluated. The latter dominates the total (dEg/dT)P of ZnP2.

    • Defects in smectic C* liquid crystals

      G S Ranganath

      More Details Abstract Fulltext PDF

      We consider the structure and properties of various topological defects that can occur in smectic C* liquid crystals. The polarization field associated with disclinations, the effect of incommensuration on the structure of dispirations, some interesting situations in the interaction between dispiration and disclination and between dispirations themselves have been discussed in detail. The properties of cholesteric type disclinations and a possible model for the core structure of a wedge disclination have also been dealt with.

    • Interaction of second sound with acoustic waves in solids

      K S Viswanathan

      More Details Abstract Fulltext PDF

      An expression has been derived for the collision operator for phonons in a solid, which is valid at very low temperatures. The set of coupled equations for the elastic deformation and the phonon density or second sound has been reduced to a simple tractable form and the dispersion equation for the coupled waves consisting of the acoustic modes and second sound has been derived. It is shown that only the longitudinal mode interacts with the second sound. It is also shown that as a result of the interaction with the second sound, the longitudinal velocity along the principal axis acquires a correction term that is proportional to bothγ2 andT4.

    • Spin fluctuation effects in substituted CeRu2Si2 and YbPd2Si2 alloys

      A M Umarji C Godart L C Gupta R Vijayaraghavan

      More Details Abstract Fulltext PDF

      Effects of chemical substitution in CeRu2Si2, a well-studied heavy fermion system and YbPd2Si2 have been investigated through magnetic susceptibility and x-ray diffraction in the systems CeRuxSi2, CeRu2−xOsxSi2, CeRu2Si2−xGex and YbPd2Si2−xGex. Replacing silicon by germanium generates normal chemical pressure effect, namely, Ce and Yb atoms in CeRu2Si2 and YbPd2Si2 became more and less magnetic respectively. With increasing Ge concentration, CeRu2Si2−xGex exhibits larger susceptibility at low temperature, goes to an antiferromagnetic state and finally becomes ferromagnetic. In YbPd2Si2−xGex, increasing Ge concentration drives Yb atoms to more divalent state. Electronic effects are more pronounced in CeRu2−xOsxSi2 though CeRu2Si2 and CeOs2Si2 have very nearly the same lattice parameters. It is conjectured that CeRu2Si2−xGex may be the first Ce-based heavy fermion having a magnetic ground state.

    • Mössbauer spectroscopy of green shale from banded iron formation

      D Das M B Chakrabarti C K Majumdar M K Bose

      More Details Abstract Fulltext PDF

      A green shale from the Precambrian banded iron formation of the Bonai Range, Eastern India, is examined by transmission Mössbauer spectroscopy. The constituent phases are identified to be chlorite, siderite and magnetite. The fractional resonance area of each constituent is computed and the ferrous-ferric ratio determined. The variation of this ratio over the sample is examined. Intensity of the magnetite lines reveals that deviation from stoichiometry is negligible. The observations suggest a transition within short range from silicate-rich facies to carbonate-oxide-rich facies in the studied section.

    • Current trends in the theories of gas-surface interaction

      Harjinder Singh B M Deb

      More Details Abstract Fulltext PDF

      Studies on gas-surface dynamics have acquired considerable importance recently not only for their intrinsic scientific interest but also for their technological potential. This article first briefly describes various experimental techniques and a number of interesting recent observations resulting from these techniques. It then discusses certain important theoretical methodologies being extensively used nowadays. There arethree broad overlapping streams of theoretical works, viz classical, semi-classical and quantum-mechanical. There are alsothree basic problems in gas-surface interaction, viz (i) the interface presents a manybody problem; (ii) the solid surface is “rough”; (iii) the number of diffractive and inelastic channels is enormously large. The semi-classical approaches appear to dominate over the others in variety and quantity. But the sources of benchmark theoretical results are still the rigorous classical-trajectory and close-coupling quantum-mechanical calculations. The coming years are likely to witness not only increased numerical accuracy through refinements in semi-classical and quantum-mechanical approaches, but also certain special approximate methods designed to yield deeper physical insights into the nature of gas-surface interaction.

  • Pramana – Journal of Physics | News

    • Editorial Note on Continuous Article Publication

      Posted on July 25, 2019

      Click here for Editorial Note on CAP Mode

© 2017-2019 Indian Academy of Sciences, Bengaluru.