Showing papers in "Pramana in 2001"
TL;DR: The soliton is the first universal concept in nonlinear science as mentioned in this paper, and its ubiquity and universality are emphasized in the special issue on nonlinear waves, solitons and their significance in physics are reviewed.
Abstract: As an introduction to the special issue on nonlinear waves, solitons and their significance in physics are reviewed. The soliton is the first universal concept in nonlinear science. Universality and ubiquity of the soliton concept are emphasized.
192 citations
TL;DR: In this article, the fundamental aspects of nonlinear optical materials and their role in modern communication are briefly reviewed and a discussion of the role of optical materials in modern communications is presented.
Abstract: In this article, we briefly review the fundamental aspects of nonlinear optical materials and their role in modern communication.
80 citations
TL;DR: It is proposed that enzymes play a crucial role in maintaining quantum coherence of the process and components of the DNA structure which implement Grover's algorithm are identified, and a physical scenario is presented for the execution of the quantum algorithm.
Abstract: Replication of DNA and synthesis of proteins are studied from the view-point of quantum database search. Identification of a base-pairing with a quantum query gives a natural (and first ever) explanation of why living organisms have 4 nucleotide bases and 20 amino acids. It is amazing that these numbers arise as solutions to an optimisation problem. Components of the DNA structure which implement Grover's algorithm are identified, and a physical scenario is presented for the execution of the quantum algorithm. It is proposed that enzymes play a crucial role in maintaining quantum coherence of the process. Experimental tests that can verify this scenario are pointed out.
77 citations
TL;DR: The historical development of optical communication systems and their failures initially are dealt with, then the different generations in optical fiber communication along with their features are discussed and their advantages and limitations are discussed.
Abstract: This paper deals with the historical development of optical communication systems and their failures initially. Then the different generations in optical fiber communication along with their features are discussed. Some aspects of total internal reflection, different types of fibers along with their size and refractive index profile, dispersion and loss mechanisms are also mentioned. Finally the general system of optical fiber communication is briefly mentioned along with its advantages and limitations. Future soliton based optical fiber communication is also highlighted.
62 citations
TL;DR: In this article, the Bianchi type IX string cosmological models in general relativity were investigated and a determinate solution was obtained by assuming a condition that the rest energy density for a cloud of strings is equal to the string tension density.
Abstract: We have investigated Bianchi type IX string cosmological models in general relativity To get a determinate solution, we have assumed a condition ρ=λ ie rest energy density for a cloud of strings is equal to the string tension density The various physical and geometrical aspects of the models are also discussed
60 citations
TL;DR: In this paper, a tutorial review is presented of the use of direct variational methods based on Rayleigh-Ritz optimization for finding approximate solutions to various nonlinear evolution equations.
Abstract: A tutorial review is presented of the use of direct variational methods based on Rayleigh-Ritz optimization for finding approximate solutions to various nonlinear evolution equations. The practical application of the approach is demonstrated by some illustrative examples in connection with the nonlinear Schrodinger equation.
56 citations
TL;DR: These steps, which start by discretizing Schrödinger’s equation, are described and a self contained introduction to quantum computing algorithms from a new perspective is provided.
Abstract: The quantum search algorithm is a technique for searching N possibilities in only O(√N) steps. Although the algorithm itself is widely known, not so well known is the series of steps that first led to it, these are quite different from any of the generally known forms of the algorithm. This paper describes these steps, which start by discretizing Schrodinger’s equation. This paper also provides a self contained introduction to quantum computing algorithms from a new perspective.
55 citations
TL;DR: In this article, the existence, stability and unique features of families of bright vortex solitons in both conservative and dissipative cubic-quintic nonlinear media are reviewed. But the results are restricted to the case of a single vortex.
Abstract: We review recent theoretical results concerning the existence, stability and unique features of families of bright vortex solitons (doughnuts, or ‘spinning’ solitons) in both conservative and dissipative cubic-quintic nonlinear media.
46 citations
TL;DR: In this article, a near-noiseless (noise figure of 0.4 dB) optical amplification of laser light in a phase-sensitive fiber amplifier was reported, which is an improvement over the theoretical limit of 1.2 dB for a conventional laser amplifier with the same gain.
Abstract: We report near-noiseless (noise figure of 0.4 dB, which is an improvement over the theoretical limit of 1.2 dB for a conventional laser amplifier with the same gain of 1.7 dB) optical amplification of laser light in a phase-sensitive fibre amplifier.
33 citations
TL;DR: In this paper, the completely integrable concept and bright, dark and self-induced transparency soliton models in nonlinear fiber optics are discussed considering the important linear and nonlinear optical effects like group velocity dispersion, higher order dispersion and Kerr nonlinearity.
Abstract: In this review, considering the important linear and nonlinear optical effects like group velocity dispersion, higher order dispersion, Kerr nonlinearity, self-steepening, stimulated Raman scattering, birefringence, self-induced transparency and various inhomogeneous effects in fibers, the completely integrable concept and bright, dark and self-induced transparency soliton models in nonlinear fiber optics are discussed. Considering the above important optical effects, the different completely integrable soliton models in the form of nonlinear Schrodinger (NLS), NLS-Maxwell-Bloch (MB) type equations reported in the literature are discussed. Finally, solitons in stimulated Raman scattering (SRS) system is briefly discussed.
27 citations
TL;DR: In this paper, the authors consider the pulse propagation in integrable Coupled Nonlinear Schrodinger Equations (CNLS) and show that the shape changes correspond to linear fractional transformations allowing for the possibility of construction of logic gates and Turing equivalent all optical computers in homogeneous bulk media.
Abstract: Coupled nonlinear Schrodinger equations (CNLS) very often represent wave propagation in optical media such as multicore fibers, photorefractive materials and so on. We consider specifically the pulse propagation in integrable CNLS equations (generalized Manakov systems). We point out that these systems possess novel exact soliton type pulses which are shape changing under collision leading to an intensity redistribution. The shape changes correspond to linear fractional transformations allowing for the possibility of construction of logic gates and Turing equivalent all optical computers in homogeneous bulk media as shown by Steiglitz recently. Special cases of such solitons correspond to the recently much discussed partially coherent stationary solitons (PCS). In this paper, we review critically the recent developments regarding the above properties with particular reference to 2-CNLS.
TL;DR: In this paper, the chiral properties of QCD were used to connect hadron masses, magnetic moments, charge radii and structure functions calculated at large quark masses within lattice QCD with the values observed physically.
Abstract: Rather than regarding the restriction of current lattice QCD simulations to quark masses that are 5--10 times larger than those observed, we note that this presents a wonderful opportunity to deepen our understanding of QCD. Just as it has been possible to learn a great deal about QCD by treating N{sub c} as a variable, so the study of hadron properties as a function of quark mass is leading us to a much deeper appreciation of hadron structure. As examples we cite recent progress in using the chiral properties of QCD to connect hadron masses, magnetic moments, charge radii and structure functions calculated at large quark masses within lattice QCD with the values observed physically.
TL;DR: In this paper, the relativistic harmonic confinement model for quarks and antiquarks was used to compute the masses of S- and P-wave mesons and pseudoscalar decay constants from light flavour to heavy flavour sectors.
Abstract: In the framework of relativistic harmonic confinement model for quarks and antiquarks, the masses of S- and P-wave mesons and pseudoscalar decay constants from light flavour to heavy flavour sectors are computed. The residual two-body Coulomb interaction and the spin-dependent interaction of the confined one gluon exchange effects (COGEP) such as spin-spin and spin-orbit interactions are perturbatively incorporated with the confinement energy to get the respective vector-pseudoscalar meson mass differences. Here we employ the same parametrization and model parameters as used in a recent study of low-lying hadron masses and leptonic decay widths. The results are being compared with the values obtained from other theoretical models and the experimental values.
TL;DR: The interactions through scalar J-couplings in NMR spin systems have been exploited to implement entangling transformations required for the three bit DJ algorithm.
Abstract: A scheme to execute an n-bit Deutsch-Jozsa (DJ) algorithm using n qubits has been implemented for up to three qubits on an NMR quantum computer. For the one- and the two-bit Deutsch problem, the qubits do not get entangled, and the NMR implementation is achieved without using spin-spin interactions. It is for the three-bit case, that the manipulation of entangled states becomes essential. The interactions through scalar J-couplings in NMR spin systems have been exploited to implement entangling transformations required for the three bit DJ algorithm.
TL;DR: This work considers the practical problem of creating a coherent superposition state of several qubits and shows that the constraints of quantum statistics require that the entropy of the system be brought down when several independent qubits are assembled together.
Abstract: Quantum computing algorithms require that the quantum register be initially present in a superposition state To achieve this, we consider the practical problem of creating a coherent superposition state of several qubits We show that the constraints of quantum statistics require that the entropy of the system be brought down when several independent qubits are assembled together In particular, we have: (i) not all initial states are realizable as pure states; (ii) the temperature of the system must be reduced These factors, in addition to decoherence and sensitivity to errors, must be considered in the implementation of quantum computers
TL;DR: In this article, the authors demonstrate that the one-and two-bit Deutsch-Jozsa algorithm does not require entanglement and can be mapped onto a classical optical scheme.
Abstract: The existence of entangled quantum states gives extra power to quantum computers over their classical counterparts. Quantum entanglement shows up qualitatively at the level of two qubits. We demonstrate that the one- and the two-bit Deutsch-Jozsa algorithm does not require entanglement and can be mapped onto a classical optical scheme. It is only for three and more input bits that the DJ algorithm requires the implementation of entangling transformations and in these cases it is impossible to implement this algorithm classically.
TL;DR: In this paper, electric field induced tunneling is studied in three different types of quantum wells by solving time-independent effective mass equation in analytic methods based on three different Airy function approaches.
Abstract: Electric field induced tunneling is studied in three different types of quantum wells by solving time-independent effective mass equation in analytic methods based on three different Airy function approaches. Comparison of different Airy function methods indicates that they are identical and connected to each other by the Breit-Wigner formula.
TL;DR: In this article, the effect of radiative cooling of electrons on the gravitational collapse of cold dust grains with fluctuating electric charge was investigated and it was shown that the radiative heating as well as the charge fluctuations, both, enhance the growth rate of the Jeans instability.
Abstract: The effect of the radiative cooling of electrons on the gravitational collapse of cold dust grains with fluctuating electric charge is investigated. We find that the radiative cooling as well as the charge fluctuations, both, enhance the growth rate of the Jeans instability. However, the Jeans length, which is zero for cold grains and nonradiative plasma, becomes finite in the presence of radiative cooling of electrons and is further enhanced due to charge fluctuations of grains resulting in an increased threshold of the spatial scale for the Jeans instability.
TL;DR: In this article, the Hartree-Fock-Roothaan (HFR) approximation for molecules, Ewald's crystal lattice theory, electromagnetic stopping theory, and other approximate methods, are evaluated and analysed in the range of 17≤n≤60 and 25≤pt≤ 60.
Abstract: Molecular auxiliary functions A
n
(p) and B
n
(pt), arising in the Hartree-Fock-Roothaan (HFR) approximation for molecules, Ewald’s crystal lattice theory, electromagnetic stopping theory, and other approximate methods, are evaluated and analysed in the range of 17≤n≤60 and 25≤pt≤60.
TL;DR: In this article, it was shown that quasiperiodic forcing is not necessary for the creation of SNAs, and that the dynamics is asymptotically on fractal attractors and the largest Lyapunov exponent is non-positive.
Abstract: We show that it is possible to devise a large class of skew-product dynamical systems which have strange nonchaotic attractors (SNAs): the dynamics is asymptotically on fractal attractors and the largest Lyapunov exponent is non-positive. Furthermore, we show that quasiperiodic forcing, which has been a hallmark of essentially all hitherto known examples of such dynamics is not necessary for the creation of SNAs.
TL;DR: In this article, pure and impurity added KDP single crystals were grown by the gel method using silica gels and X-ray diffraction data were collected for powder samples and used for the estimation of lattice variation and thermal parameters like Debye-Waller factor, mean square amplitude of vibration, Debye temperature and Debye frequency.
Abstract: Pure and impurity added (with NH4Cl, NH4NO3, NH4H2PO4, and (NH4)2SO4) KDP single crystals were grown by the gel method using silica gels. X-ray diffraction data were collected for powder samples and used for the estimation of lattice variation and thermal parameters like Debye-Waller factor, mean-square amplitude of vibration, Debye temperature and Debye frequency. The thermal parameters do not vary in a particular order with respect to impurity concentration. The results obtained are reported and discussed.
TL;DR: The models of the nonlinear optics in which solitons appeared are considered in this paper, which are of paramount importance in studies of nonlinear wave phenomena, such as self-focusing, self-induced transparency and parametric interaction of three waves.
Abstract: The models of the nonlinear optics in which solitons appeared are considered. These models are of paramount importance in studies of nonlinear wave phenomena. The classical examples of phenomena of this kind are the self-focusing, self-induced transparency and parametric interaction of three waves. At present there are a number of theories based on completely integrable systems of equations, which are, both, generations of the original known models and new ones. The modified Korteweg-de Vries equation, the nonlinear Schrodinger equation, the derivative nonlinear Schrodinger equation. Sine-Gordon equation, the reduced Maxwell-Bloch equation. Hirota equation, the principal chiral field equations, and the equations of massive Thirring model are some soliton equations, which are usually to be found in nonlinear optics theory.
TL;DR: In this paper, the current status of the nuclear matter incompressibility coefficient, K ≥ 0, was reviewed, and the theoretical and experimental methods used to determine K ≥ 1.
Abstract: We review the current status of the nuclear matter (N=Z and no Coulomb interaction) incompressibility coefficient, K
nm
, and describe the theoretical and the experimental methods used to determine K
nm
from properties of compression modes in nuclei. In particular we consider the long standing problem of the conflicting results obtained for K
nm
, deduced from experimental data on excitation cross sections for the isoscalar giant monopole resonance (ISGMR) and data for the isoscalar giant dipole resonance (ISGDR).
TL;DR: In this article, the role of soliton-based communications research in present day ultra-high speed communications is discussed, and an overview of the current state of the art is presented.
Abstract: Multi-terabit/s, ultra-high speed optical transmissions over several thousands kilometers on fibers are becoming a reality. Most use RZ (Return to Zero) format in dispersion-managed fibers. This format is the only stable waveform in the presence of fiber Kerr nonlinearity and dispersion in all optical transmission lines with loss compensated by periodic amplifications. The nonlinear Schrodinger equation assisted by the split step numerical solutions is commonly used as the master equation to describe the information transfer in optical fibers. All these facts are the outcome of research on optical solitons in fibers in spite of the fact that the commonly used RZ format is not always called a soliton format. The overview presented here attempts to incorporate the role of soliton-based communications research in present day ultra-high speed communications.
TL;DR: In this paper, the authors compared the non-linear wave packet dynamics of coherent states of various symmetry groups and found that certain generic features of nonlinear evolution are present in each case.
Abstract: We have compared the non-linear wave packet dynamics of coherent states of various symmetry groups and found that certain generic features of non-linear evolution are present in each case. Thus the initial coherent structures are quickly destroyed but are followed by Schrodinger cat formation and revival. We also report important differences in their evolution.
TL;DR: In this paper, the authors studied the behavior of sheath structure in a multi-component plasma with dust-neutral collisions and calculated the sheath-edge potential and sheath width for collisionally dominated sheath.
Abstract: The aim of this brief report is to study the behaviour of sheath structure in a multi-component plasma with dust-neutral collisions. The plasma consists of electrons, ions, micron size negatively charged dust particles and neutrals. The sheath-edge potential and sheath width are calculated for collisionally dominated sheath. Comparison of collisionless and collisionally dominated sheath are made.
TL;DR: In this article, the existence of fully stable spinning solitons in optical fibres with self-focusing Kerr (cubic) nonlinearity, and in bulk media featuring a combination of the cubic self-defocusing and quadratic nonlinearities, was investigated.
Abstract: We present a review of new results which suggest the existence of fully stable spinning solitons (self-supporting localised objects with an internal vorticity) in optical fibres with self-focusing Kerr (cubic) nonlinearity, and in bulk media featuring a combination of the cubic self-defocusing and quadratic nonlinearities. Their distinctive difference from other optical solitons with an internal vorticity, which were recently studied in various optical media, theoretically and also experimentally, is that all the spinning solitons considered thus far have been found to be unstable against azimuthal perturbations. In the first part of the paper, we consider solitons in a nonlinear optical fibre in a region of parameters where the fibre carries exactly two distinct modes, viz., the fundamental one and the first-order helical mode. From the viewpoint of application to communication systems, this opens the way to doubling the number of channels carried by a fibre. Besides that, these solitons are objects of fundamental interest. To fully examine their stability, it is crucially important to consider collisions between them, and their collisions with fundamental solitons, in (ordinary or hollow) optical fibres. We introduce a system of coupled nonlinear Schrodinger equations for the fundamental and helical modes with nonstandard values of the cross-phase-modulation coupling constants, and show, in analytical and numerical forms, results of collisions between solitons carried by the two modes. In the second part of the paper, we demonstrate that the interaction of the fundamental beam with its second harmonic in bulk media, in the presence of self-defocusing Kerr nonlinearity, gives rise to the first ever example of completely stable spatial ring-shaped solitons with intrinsic vorticity. The stability is demonstrated both by direct simulations and by analysis of linearized equations.
TL;DR: The production of single photons in Pb+Pb collisions at the CERN SPS as measured by the WA98 experiment is analysed in this article, where a quark gluon plasma is assumed to be formed initially, which expands, cools, hadronizes, and undergoes freeze-out.
Abstract: The production of single photons in Pb+Pb collisions at the CERN SPS as measured by the WA98 experiment is analysed A quark gluon plasma is assumed to be formed initially, which expands, cools, hadronizes, and undergoes freeze-out A rich hadronic equation of state is used and the transverse expansion of the interacting system is taken into account The recent estimates of photon production in quark-matter (at two loop level) along with the dominant reactions in the hadronic matter leading to photons are used About half of the radiated photons are seen to have a thermal origin The same treatment and the initial conditions provide a very good description to hadronic spectra measured by several groups and the intermediate mass dileptons measured by the NA50 experiment, lending a strong support to the conclusion that quark gluon plasma has been formed in these collisions Predictions for RHIC and LHC energies are also given
TL;DR: In this article, a repulsive part is introduced in the interaction between the core and the extra-core neutron, to simulate Pauli principle, and two neutron separation energy, r.m.s. radii, correlation factor and probability density distributions have been calculated.
Abstract: Hyperspherical harmonics expansion method is applied to a three-body model of two neutron halo nuclei. Convergence of the expansion has been ensured. A repulsive part is introduced in the interaction between the core and the extra-core neutron, to simulate Pauli principle. Two neutron separation energy, r.m.s. radii, correlation factor and probability density distributions have been calculated for 6He. It is found that the convergence of the two neutron separation energy is relatively slow, while other quantities reach convergence quickly.
TL;DR: In this paper, a summary of the case for considering hidden variable models which, in abandoning this independence assumption, allow a degree of "backward causation" is given. But this assumption rests on surprisingly shaky ground: it is puzzlingly time-asymmetric.
Abstract: Bell’s theorem requires the assumption that hidden variables are independent of future measurement settings. This independence assumption rests on surprisingly shaky ground. In particular, it is puzzlingly time-asymmetric. The paper begins with a summary of the case for considering hidden variable models which, in abandoning this independence assumption, allow a degree of ‘backward causation’. The remainder of the paper clarifies the physical significance of such models, in relation to the issue as to whether quantum mechanics provides a complete description of physical reality.