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  • 1. Agarwal, Sahil
    et al.
    Wettlaufer, John S.
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Maximal stochastic transport in the Lorenz equations2016In: Physics Letters A, ISSN 0375-9601, E-ISSN 1873-2429, Vol. 380, no 1-2, p. 142-146Article in journal (Refereed)
    Abstract [en]

    We calculate the stochastic upper bounds for the Lorenz equations using an extension of the background method. In analogy with Rayleigh-Benard convection the upper bounds are for heat transport versus Rayleigh number. As might be expected, the stochastic upper bounds are larger than the deterministic counterpart of Souza and Doering [1], but their variation with noise amplitude exhibits interesting behavior. Below the transition to chaotic dynamics the upper bounds increase monotonically with noise amplitude. However, in the chaotic regime this monotonicity depends on the number of realizations in the ensemble; at a particular Rayleigh number the bound may increase or decrease with noise amplitude. The origin of this behavior is the coupling between the noise and unstable periodic orbits, the degree of which depends on the degree to which the ensemble represents the ergodic set. This is confirmed by examining the close returns plots of the full solutions to the stochastic equations and the numerical convergence of the noise correlations. The numerical convergence of both the ensemble and time averages of the noise correlations is sufficiently slow that it is the limiting aspect of the realization of these bounds. Finally, we note that the full solutions of the stochastic equations demonstrate that the effect of noise is equivalent to the effect of chaos.

  • 2. Allaoui, Aissa
    et al.
    Toll, Staffan
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Evesque, Pierre
    Bai, JinBo
    On the compressive response of carbon nanotube tangles2009In: Physics Letters A, ISSN 0375-9601, E-ISSN 1873-2429, Vol. 373, no 35, p. 3169-3173Article in journal (Refereed)
    Abstract [en]

    The nonlinear bulk compressibility of entangled multiwalled carbon nanotubes is studied. The analogy with textile fibre assemblies is explored by means of the well established van Wyk model. In view of the small diameter of the nanotubes. the possible effect of adhesive van der Waals interactions at tube-tube contacts is analysed. It is found, however, that the contribution of adhesive contacts to the bulk stress should be negligible. Compression experiments are performed on multi-walled carbon nanotubes and show that van Wyk's model is able to describe the response, although the values of the dimensionless parameter k of van Wyk's model were lower than expected. There is indeed no indication that van der Waals interactions play any significant role.

  • 3. Andersen, T.
    et al.
    Keller, O.
    Hubner, W.
    Johansson, Börje
    Spin response in nonlocal nonlinear optics2004In: Physics Letters A, ISSN 0375-9601, E-ISSN 1873-2429, Vol. 320, no 06-maj, p. 465-470Article in journal (Refereed)
  • 4. Basylko, S. A.
    et al.
    Onischouk, V. A.
    Kundrotas, P. J.
    Tornau, E. E.
    Rosengren, Anders
    KTH, Superseded Departments, Physics.
    Ground-state study of a donor-acceptor model with finite charge-transfer energy2000In: Physics Letters A, ISSN 0375-9601, E-ISSN 1873-2429, Vol. 271, no 02-jan, p. 134-138Article in journal (Refereed)
    Abstract [en]

    A donor-acceptor model with randomly distributed N donor and N acceptor sites and with finite charge transfer energy Delta is investigated at zero temperature by means of computer simulations on two-dimensional samples of different sizes, We demonstrate that the density of one-electron excitations g(epsilon) for accepters in the vicinity of the Fermi energy mu depends essentially on the size of the sample investigated and that g(epsilon) further away from mu exhibits a size-independent power-law with the non-universal exponent decreasing with increasing Delta. Rigorous relations for mu and for the mapping of g(epsilon) for donors into g(epsilon) for accepters are also given.

  • 5. Basylko, S. A.
    et al.
    Onischouk, V. A.
    Rosengren, Anders
    KTH, Superseded Departments, Physics.
    Coulomb glass in the restricted random phase approximation2002In: Physics Letters A, ISSN 0375-9601, E-ISSN 1873-2429, Vol. 298, no 06-maj, p. 416-421Article in journal (Refereed)
    Abstract [en]

    A three-dimensional model of N/2 electrons localized on N randomly distributed donor sites of density n and with the acceptor charge uniformly smeared on these sites, -e/2 on each. has been considered in the restricted random phase approximation (RRPA) which uses the set of 3N Fourier components of the local charge density as the independent collective variables. The energy e(T) per site and the density of one-site excitation energy (DOSE) g(epsilon) are shown to he, respectively, in excellent quantitative and in good qualitative agreement with the Monte Carlo simulation data in the whole temperature region 0.1 < T < 100, where these simulations were performed (e(2)n(1/3)/k(B) being the temperature scale). The pair correlator for the one-site energies g(epsilon,+/-epsilon, r) is found to have the slow decoupling law similar to(+/-1/r) for T less than or similar to 1 and r much greater than r(d) (r(d), Debye screening radius). The status of the commonly accepted asymptotic g(epsilon) similar to (epsilon - mu)(d-1) (d and mu being, respectively, the spatial dimension and the Fermi energy) is discussed. The deduction of this asymptotic is shown to be based on the strong and questionable conjecture about decoupling of correlations between one-site excitation energies in the vicinity of mu.

  • 6.
    Bonnaud, Etienne L.
    et al.
    KTH, Superseded Departments, Solid Mechanics.
    Neumeister, Jonas M.
    KTH, Superseded Departments, Solid Mechanics.
    Inertia and damping effects on the damage-dependent burst size distribution of fiber bundles2001In: Physics Letters A, ISSN 0375-9601, E-ISSN 1873-2429, Vol. 290, p. 261-269Article in journal (Refereed)
    Abstract [en]

    Distributions of simultaneous fiber failures—bursts—in loaded fiber bundles are studied considering inertia and damping. Resulting burst size distributions have universal properties: all approach the power law DΔΔ−2.5 for larger burst sizes Δ. Momentary burst size distributions evolve with increasing damage and do not follow power laws but are still universal. Finally, it is briefly outlined how to use distribution progression to assess damage state.

  • 7. Borman, V. D.
    et al.
    Johansson, Börje
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Skorodumova, N. V.
    Tronin, I. V.
    Tronin, V. N.
    Troyan, V. I.
    Diffusion and particle mobility in 1D system2006In: Physics Letters A, ISSN 0375-9601, E-ISSN 1873-2429, Vol. 359, no 5, p. 504-508Article in journal (Refereed)
  • 8. Boswell, C. J.
    et al.
    Berk, H. L.
    Borba, D. N.
    Johnson, Thomas J.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Pinches, S. D.
    Sharapov, S. E.
    Observation and explanation of the JET n=0 chirping mode2006In: Physics Letters A, ISSN 0375-9601, E-ISSN 1873-2429, Vol. 358, no 2, p. 154-158Article in journal (Refereed)
    Abstract [en]

    Persistent rapid up and down frequency chirping modes with a toroidal mode number of zero (n = 0) have been observed in the JET tokamak when energetic ions, with a mean energy similar to 500 keV, were created by high field side ion cyclotron resonance frequency heating. This heating method enables the formation of an energetically inverted ion distribution function that allows ions to spontaneously excite the observed instability, identified as a global geodesic acoustic mode. The interpretation is that phase space structures form and interact with the fluid zonal flow to produce the pronounced frequency chirping.

  • 9.
    Cai, Yangjian
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering. KTH, School of Information and Communication Technology (ICT), Centres, Zhejiang-KTH Joint Research Center of Photonics, JORCEP.
    Ge, Di
    Propagation of various dark hollow beams through an apertured paraxial ABCD optical system2006In: Physics Letters A, ISSN 0375-9601, E-ISSN 1873-2429, Vol. 357, no 1, p. 72-80Article in journal (Refereed)
    Abstract [en]

    Propagation of a dark hollow beam (DHB) of circular, elliptical or rectangular symmetry through an apertured paraxial ABCD optical system is investigated. Approximate analytical formulas for various DHBs propagating through an apertured paraxial optical system are derived by expanding the hard-aperture function into a finite sum of complex Gaussian functions in terms of a tensor method. Some numerical results are given. Our formulas provide a convenient way for studying the propagation of various DHBs through an apertured paraxial optical system.

  • 10. Constantin, A.
    et al.
    Kolev, B.
    Lenells, Jonatan
    Department of Mathematics, Lund University, 22100 Lund, Sweden .
    Integrability of invariant metrics on the Virasoro group2006In: Physics Letters A, ISSN 0375-9601, E-ISSN 1873-2429, Vol. 350, no 1-2, p. 75-80Article in journal (Refereed)
    Abstract [en]

    Each right-invariant metric on the Virasoro group induces a Hamiltonian vector field on the dual of the Lie algebra vir equipped with the canonical Lie-Poisson structure. We show that the Hamiltonian vector fields Xk induced by the metrics given at the identity by the Hk Sobolev inner products, k≥0, are bi-Hamiltonian relative to a modified Lie-Poisson structure only for k=0 and k=1.

  • 11. Constantin, A.
    et al.
    Lenells, Jonatan
    Department of Mathematics, Lund University, PO Box 118, 22100 Lund, Sweden .
    On the inverse scattering approach for an integrable shallow water wave equation2003In: Physics Letters A, ISSN 0375-9601, E-ISSN 1873-2429, Vol. 308, no 5-6, p. 432-436Article in journal (Refereed)
    Abstract [en]

    We present an algorithm for the inverse scattering problem associated to a nonlinear equation arising in the study of the unidirectional propagation of waves in shallow water.

  • 12. Dyakonov, V.
    et al.
    Prohorov, A.
    Shapovalov, V.
    Khartsev, Sergiy
    Krivoruchko, V.
    Mihailov, V.
    Pashchenko, V.
    Zubov, E.
    Aleshkevych, P.
    Dyakonov, K.
    Piechota, S.
    Szymczak, H.
    Spin-wave resonance in the La0.7Mn1.3O3-delta film2000In: Physics Letters A, ISSN 0375-9601, E-ISSN 1873-2429, Vol. 268, no 3, p. 202-207Article in journal (Refereed)
    Abstract [en]

    The spin-wave resonance (SWR) spectra have been observed in the (001) oriented La0.7Mn1.3O3-delta epitaxial films. The spectra consist of a series of well-resolved spin-wave modes clearly seen in the: perpendicular external field configuration. It is shown that the spins are completely pinned on both sides of the film surface. Based on a study of the SWR spectra the value of the spin-wave exchange constant, D, is found to be 150 meV Angstrom(2). This value of. D correlates well with this one determined for all known until now manganites.

  • 13. Fasoli, A.
    et al.
    Jaun, André
    KTH, Superseded Departments, Alfvén Laboratory.
    Testa, D.
    Isotope mass scaling of AE damping rates in the JET tokamak plasmas2000In: Physics Letters A, ISSN 0375-9601, E-ISSN 1873-2429, Vol. 265, no 4, p. 288-293Article in journal (Refereed)
    Abstract [en]

    The damping of radially extended Alfven eigenmodes in tokamak plasmas is investigated in JET discharges with different ion mass. The comparison of damping measurements with predictions of a gyro-kinetic model indicates that mode conversion into kinetic Alfven waves is the dominant damping mechanism for Alfven eigenmodes in the plasma core.

  • 14. Fiolhais, Miguel C. N.
    et al.
    Essén, Hanno
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Gouveia, Tome M.
    A variational proof of Thomson's theorem2016In: Physics Letters A, ISSN 0375-9601, E-ISSN 1873-2429, Vol. 380, no 35, p. 2703-2705Article in journal (Refereed)
    Abstract [en]

    Thomson's theorem of electrostatics, which states the electric charge on a set of conductors distributes itself on the conductor surfaces to minimize the electrostatic energy, is reviewed in this letter. The proof of Thomson's theorem, based on a variational principle, is derived for a set of normal charged conductors, with and without the presence of external electric fields produced by fixed charge distributions. In this novel approach, the variations are performed on both the charge densities and electric potentials, by means of a local Lagrange multiplier associated with Poisson's equation, constraining the two variables.

  • 15. Ghiu, I.
    et al.
    Bourennane, M.
    Karlsson, Anders
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Entanglement-assisted local transformations between inequivalent classes of three-particle entangled states2001In: Physics Letters A, ISSN 0375-9601, E-ISSN 1873-2429, Vol. 287, no 02-jan, p. 12-18Article in journal (Refereed)
    Abstract [en]

    We show that bipartite and tripartite entangled states cannot be used as catalysis states to enable local transformations inbetween inequivalent classes of three-particle entangled states which are non-interchangeable under local transformations. We find the optimal protocol for conversion of a certain family of the W-states and an EPR-pair into the GHZ-state.

  • 16.
    Hu, Li
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering. KTH, School of Information and Communication Technology (ICT), Centres, Zhejiang-KTH Joint Research Center of Photonics, JORCEP.
    Cai, Yangjian
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering. KTH, School of Information and Communication Technology (ICT), Centres, Zhejiang-KTH Joint Research Center of Photonics, JORCEP.
    Analytical formula for a circular flattened Gaussian beam propagating through a misaligned paraxial ABCD optical system2006In: Physics Letters A, ISSN 0375-9601, E-ISSN 1873-2429, Vol. 360, no 2, p. 394-399Article in journal (Refereed)
    Abstract [en]

    Based on the generalized diffraction integral formula for treating the propagation of a laser beam through a misaligned paraxial ABCD optical system in the cylindrical coordinate system, analytical formula for a circular flattened Gaussian beam propagating through such optical system is derived. Furthermore, an approximate analytical formula is derived for a circular flattened Gaussian beam propagating through an apertured misaligned ABCD optical system by expanding the hard aperture function as a finite sum of complex Gaussian functions. Numerical examples are given.

  • 17. Jin, Y.
    et al.
    He, J. L.
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Surface polaritons and slow propagation related to chiral media supporting backward waves2006In: Physics Letters A, ISSN 0375-9601, E-ISSN 1873-2429, Vol. 351, no 04-5, p. 354-358Article in journal (Refereed)
  • 18. Jin, Yi
    et al.
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Negative refraction of complex lattices of dielectric cylinders2007In: Physics Letters A, ISSN 0375-9601, E-ISSN 1873-2429, Vol. 360, no 3, p. 461-466Article in journal (Refereed)
  • 19. Kundrotas, P. J.
    et al.
    Onischouk, V. A.
    Rosengren, Anders
    KTH, Superseded Departments, Physics.
    Coulomb correlation gap: Finite-size analysis2001In: Physics Letters A, ISSN 0375-9601, E-ISSN 1873-2429, Vol. 287, no 04-mar, p. 278-282Article in journal (Refereed)
    Abstract [en]

    A semiclassical model with randomly distributed N donor and K x N acceptor sites and with infinite-range Coulomb interaction is investigated by means of computer simulations on two-dimensional samples of different sizes. The shape of the Coulomb correlation gap in the density of one-electron excitations g(epsilon) is obtained for different values of K within a wide energy interval around the Fermi energy mu. Using simple scaling arguments we demonstrate that the true behavior of g(epsilon) in the immediate neighborhood of mu is hidden by the finite-size effects and find that g(epsilon) further away from mu is described by a power-law with an exponent, depending on K and the sign of epsilon - mu.

  • 20.
    Langmann, Edwin
    KTH, School of Engineering Sciences (SCI), Physics, Mathematical Physics. KTH, School of Engineering Sciences (SCI), Physics, Condensed Matter Theory.
    Supersymmetry breaking and the Jaynes-Cummings model1993In: Physics Letters A, ISSN 0375-9601, E-ISSN 1873-2429, Vol. 176, no 5, p. 307-312Article in journal (Refereed)
  • 21. Lue, Xiang
    et al.
    Cai, Yangjian
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Partially coherent circular and elliptical dark hollow beams and their paraxial propagations2007In: Physics Letters A, ISSN 0375-9601, E-ISSN 1873-2429, Vol. 369, no 1-2, p. 157-166Article in journal (Refereed)
    Abstract [en]

    A theoretical model is proposed to describe a partially coherent dark hollow beam (DHB) of circular or elliptical symmetry. The characteristics of the partially coherent circular or elliptical DHB can be easily controlled by properly choosing the beam parameters. Based on the generalized Collins integral, analytical formulas for a partially coherent circular or elliptical DHB propagating through paraxial aligned and misaligned optical systems are derived. Some numerical examples are illustrated. Our model provides a convenient way to describe and treat the propagation of partially coherent circular and elliptical DHBs.

  • 22.
    Manyuhina, Oksana V.
    et al.
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Ben Amar, M.
    Thin nematic films: Anchoring effects and stripe instability revisited2013In: Physics Letters A, ISSN 0375-9601, E-ISSN 1873-2429, Vol. 377, no 13, p. 1003-1011Article in journal (Refereed)
    Abstract [en]

    We study theoretically the formation of long-wavelength instability patterns observed at spreading of nematic droplets on liquid substrates. The role of surface-like elastic terms in nematic films of submicron thickness is (re)examined by extending our previous work to hybrid aligned nematics. We identify the upper threshold for the formation of stripes and compare our results with experimental observations. We find that the wavelength and the amplitude of the in-plane director undulations can be related to the small but finite azimuthal anchoring. Within a simplified model we analyse the possibility of non-planar base state below the Barbero-Barberi critical thickness.

  • 23. Osipov, G.V.
    et al.
    Kozlov, Alexander
    KTH, School of Computer Science and Communication (CSC), Computational Biology, CB.
    Shalfeev, V.D.
    Impulse control of chaos in continuous systems1998In: Physics Letters A, ISSN 0375-9601, E-ISSN 1873-2429, Vol. 247, no 1-2, p. 119-128Article in journal (Refereed)
    Abstract [en]

    Several methods of nonconstant feedback impulse control of chaos are proposed. The approach is based on the similarity of the return maps of dissipative continuous-time systems with one-dimensional maps and has a clear geometrical interpretation. The methods are illustrated for Chua's circuit, the Rossler oscillator, and the phase-locked loop system. (C) 1998 Elsevier Science B.V.

  • 24.
    Qiu, Min
    et al.
    KTH, Superseded Departments, Electromagnetic Theory.
    He, Sailing
    KTH, Superseded Departments, Electromagnetic Theory.
    FDTD algorithm for computing the off-plane band structure in a two-dimensional photonic crystal with dielectric or metallic inclusions2001In: Physics Letters A, ISSN 0375-9601, E-ISSN 1873-2429, Vol. 278, no 6, p. 348-354Article in journal (Refereed)
    Abstract [en]

    An effective numerical method based on the finite-difference time-domain scheme for computing the off-plane band structure of a two-dimensional photonic crystal is presented. The method is an order N method, and requires only a two-dimensional discretization mesh for a given off-plant wave number k(z) although thr off-plane propagation is a three-dimensional problem. The computation time and memory required is thus reduced significantly. The present method can be used for any type of inclusions and no additional effort is needed for metallic inclusions. The off-plane band structures of a square lattice of metallic rods in the air are studied, and a complete bandgap for some nonzero off-plane wave number k(z) is found.

  • 25.
    Qiu, Min
    et al.
    KTH, Superseded Departments, Electromagnetic Theory.
    He, Sailing
    KTH, Superseded Departments, Electromagnetic Theory.
    Guided modes in a two-dimensional metallic photonic crystal waveguide2000In: Physics Letters A, ISSN 0375-9601, E-ISSN 1873-2429, Vol. 266, no 4-6, p. 425-429Article in journal (Refereed)
    Abstract [en]

    Guided modes in a two-dimensional metallic photonic crystal waveguide are studied. The guided modes in the photonic crystal waveguide are related to those in a conventional metallic waveguide. There exists a cutoff frequency and consequently a mode gap at low frequencies (starting from zero frequency) in the photonic crystal metallic waveguide.

  • 26.
    Qiu, Min
    et al.
    KTH, Superseded Departments, Electromagnetic Theory.
    He, Sailing
    KTH, Superseded Departments, Electromagnetic Theory.
    Surface modes in two-dimensional dielectric and metallic photonic band gap structures: a FDTD study2001In: Physics Letters A, ISSN 0375-9601, E-ISSN 1873-2429, Vol. 282, no 1-2, p. 85-91Article in journal (Refereed)
    Abstract [en]

    In the present Letter, surface modes in two-dimensional dielectric and metallic photonic crystals are studied by a finite-difference time-domain method. The existence of surface modes in metallic photonic crystals is examined. The influence of surface waves on dielectric photonic crystal antennas is also studied.

  • 27.
    Raadu, Michael A.
    et al.
    KTH, Superseded Departments, Alfvén Laboratory.
    Shafiq, Muhammad
    KTH, Superseded Departments, Alfvén Laboratory.
    Test charge response of a dusty plasma with a grain size distribution2002In: Physics Letters A, ISSN 0375-9601, E-ISSN 1873-2429, Vol. 305, p. 79-86Article in journal (Refereed)
    Abstract [en]

    The form of the grain size distribution strongly influences the linear dielectric response of a dusty plasma. For a class of size distributions there is an equivalence to a Lorentzian distribution of mono-sized particles. The electrostatic response to a slowly moving test charge, using a second order approximation, is found. The effects of collisions are investigated.

  • 28.
    Shen, Jian Qi
    KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Photonic-resonant left-handed medium2006In: Physics Letters A, ISSN 0375-9601, E-ISSN 1873-2429, Vol. 357, no 1, p. 54-60Article in journal (Refereed)
    Abstract [en]

    A new scheme to realize simultaneously negative permittivity and permeability in a coherent atomic vapor medium (photonic-resonant material) via a coherent driving mechanism is suggested. It is verified that the atomic system coherently driven by a strong optical field will give rise to a negative refractive index in certain probe frequency ranges. One of the most remarkable features of the present scheme is such that a slab fabricated by the left-handed vapor medium is an ideal candidate for designing perfect lenses since the photonic-resonant atomic vapor cannot only exhibit an isotropic negative refractive index, but also provide a good impedance match at the air-medium interfaces.

  • 29. Shen, Jianqi
    Nonanalytic metric in the presence of gravitomagnetic monopoles2005In: Physics Letters A, ISSN 0375-9601, E-ISSN 1873-2429, Vol. 340, no 1-4, p. 12-17Article, review/survey (Refereed)
    Abstract [en]

    The nonanalytic property of metric resulting from the presence of gravitomagnetic monopoles is considered. The curvature tensors, dual curvature tensors, dual Einstein tensor (and hence the gravitational field equation of gravitomagnetic matter) expressed in terms of nonanalytic metric are analyzed. It is shown that the spinor gravitomagnetic monopole may be one of the potential origins of the cosmological constant. An alternative approach to the cosmological constant problem is thus proposed based on the concept of gravitomagnetic monopole.

  • 30.
    Shen, Jianqi
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Optical refractive index of massive particles and physical meanings of left-handed media2005In: Physics Letters A, ISSN 0375-9601, E-ISSN 1873-2429, Vol. 344, no 2-4, p. 144-148Article in journal (Refereed)
    Abstract [en]

    In this Letter the expression for the refractive index of de Broglie wave in the presence of a potential field is obtained and based on this, the physical meanings of negative index of refraction is revealed. We demonstrate that the electromagnetic wave propagation in a left-handed medium with negative refractive index behaves just like that of antiphotons, which is required of the complex vector field theory. It is believed that the complex vector field theory is helpful in considering the wave propagation and photonic band gap structures in the left-handed medium photonic crystals with a periodicity in negative and positive indices of refraction.

  • 31.
    Shen, Jianqi
    et al.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Ruan, Zhichao
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    He, Sailing
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Influence of the signal light on the transient optical properties of a four-level EIT medium2004In: Physics Letters A, ISSN 0375-9601, E-ISSN 1873-2429, Vol. 330, p. 487-495Article in journal (Refereed)
    Abstract [en]

    General formulae for the transient evolution of the susceptibility (absorption) induced by the quantum interference effect in a four-level N-type EIT medium is presented. The influence of the signal light on the transient susceptibility for the probe beam is studied for two typical cases when the strength of the coupling beam is much greater or less than that of the signal field. An interesting level reciprocity relationship between these two cases is found.

  • 32. Shen, L. F.
    et al.
    He, Sailing
    KTH, Superseded Departments, Electromagnetic Theory.
    Studies of imaging characteristics for a slab of a lossy left-handed material2003In: Physics Letters A, ISSN 0375-9601, E-ISSN 1873-2429, Vol. 309, no 03-4, p. 298-305Article in journal (Refereed)
  • 33. Simovski, C. R.
    et al.
    He, Sailing
    KTH, Superseded Departments, Electromagnetic Theory.
    Frequency range and explicit expressions for negative permittivity and permeability for an isotropic medium formed by a lattice of perfectly conducting Omega particles2003In: Physics Letters A, ISSN 0375-9601, E-ISSN 1873-2429, Vol. 311, no 02-3, p. 254-263Article in journal (Refereed)
  • 34.
    Song, Yubao
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL. National University of Defense Technology, People's Republic of China .
    Feng, Leping
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Wen, Jihong
    Yu, Dianong
    Wen, Xisen
    Analysis and enhancement of flexural wave stop bands in 2D periodic plates2015In: Physics Letters A, ISSN 0375-9601, E-ISSN 1873-2429, Vol. 379, no 22-23Article in journal (Other academic)
    Abstract [en]

    The band structure and enhancement of flexural wave stop bands in a 2D periodic plate are investigated. A unified method for analysing and designing the stop band of the plates with various attached structures is proposed. The effect of attached structures is considered based on their equivalent parameters (added equivalent mass and equivalent moment of inertia). The influences of the equivalent parameters on the band structures are studied. Three cases are considered: adding pure equivalent mass, pure equivalent moment of inertia and the combination of these two. The stop bands are enhanced via the multi interaction between the host plate and the attached structure. The enhancement pattern is determined, and several ways to obtain a wider combined stop band are presented. The frequency response functions of corresponding finite periodic plates are calculated to verify the stop bands and their enhancement in a number of typical cases.

  • 35. Tracy, E. R.
    et al.
    Kaufman, A. N.
    Jaun, André
    KTH, Superseded Departments, Alfvén Laboratory.
    A ray-based algorithm for multi-dimensional linear conversion2001In: Physics Letters A, ISSN 0375-9601, E-ISSN 1873-2429, Vol. 290, no 06-maj, p. 309-316Article in journal (Refereed)
    Abstract [en]

    A numerical algorithm is proposed for connecting the incoming and outgoing wave fields in studies of linear conversion. This is the first such ray-based algorithm for wave conversion in multiple spatial dimensions. It is demonstrated that, aside from the overall phase of the coupling, one can directly evaluate all quantities needed for the connection coefficients from the ray geometry. The ray dynamics is generated using the determinant of the dispersion matrix as the Hamiltonian. Using information available while following an incoming ray, the algorithm automatically detects that the ray has entered a conversion region, evaluates the transmission and conversion coefficients, and launches the transmitted ray. The algorithm does not require any prior knowledge of the geometry of the conversion region. The algorithm is illustrated using a two-dimensional toroidal model with resonant conversion from a magnetosonic to an ion-hybrid wave.

  • 36.
    Valiev, Damir
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Bychkov, Vitaly
    Department of Physics, Umeå University.
    Akkerman, V'yacheslav
    Department of Physics, Umeå University.
    Eriksson, Lars-Erik
    Department of Thermo- and Fluid Dynamics, Chalmers University of Technology.
    Marklund, Mattias
    Department of Physics, Umeå University.
    Heating of the fuel mixture due to viscous stress ahead of accelerating flames in deflagration-to-detonation transition2008In: Physics Letters A, ISSN 0375-9601, E-ISSN 1873-2429, Vol. 372, no 27-28, p. 4850-4857Article in journal (Refereed)
    Abstract [en]

    The role of viscous stress in heating of the fuel mixture in deflagration-to-detonation transition in tubes is studied both analytically and numerically. The analytical theory is developed in the limit of low Mach number; it determines temperature distribution ahead of an accelerating flame with maximum achieved at the walls. The heating effects of viscous stress and the compression wave become comparable at sufficiently high values of the Mach number. In the case of relatively large Mach number, viscous heating is investigated by direct numerical simulations. The simulations were performed on the basis of compressible Navier–Stokes gas-dynamic equations taking into account chemical kinetics. In agreement with the theory, viscous stress makes heating and explosion of the fuel mixture preferential at the walls. The explosion develops in an essentially multi-dimensional way, with fast spontaneous reaction spreading along the walls and pushing inclined shocks. Eventually, the combination of explosive reaction and shocks evolves into detonation.

  • 37.
    Vargunin, Artjom
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics. University of Tartu, Estonia.
    Rago, Kullike
    Ord, Teet
    Unusual boundary effect on coherency in two-band superconductors2017In: Physics Letters A, ISSN 0375-9601, E-ISSN 1873-2429, Vol. 381, no 37, p. 3241-3245Article in journal (Refereed)
    Abstract [en]

    We demonstrate that restoration of two-band superconductivity near the surface of the system is governed by length scales which are drastically different from correlation lengths. Similar to the one band case, one of the characteristic lengths diverges at critical temperature T-c, while another one shows unusual behaviour having singularity at Tc+ < T-c. By moving away from the boundary, these scales approach correlation lengths in the bulk state, where the divergence at Tc+ is removed by arbitrary weak interband coupling. The peculiarity can be manifested in proximity sandwich where Tc+ becomes an inflection point for critical temperature being a function of superconducting layer thickness.

  • 38. Vekilov, Y. K.
    et al.
    Isaev, E. I.
    Johansson, Börje
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Does the Wiedemann-Franz law work for quasicrystals?2006In: Physics Letters A, ISSN 0375-9601, E-ISSN 1873-2429, Vol. 352, no 6, p. 524-525Article in journal (Refereed)
  • 39. Voloshin, V. A.
    et al.
    Gusev, A. A.
    Danilenko, I. A.
    Medvedeva, L. I.
    Prokhorov, A. D.
    Khartsev, Sergiy
    Interplay of structure, magnetism and resistivity of La0.5Ca0.54MnO3+x2000In: Physics Letters A, ISSN 0375-9601, E-ISSN 1873-2429, Vol. 271, no 02-jan, p. 121-127Article in journal (Refereed)
    Abstract [en]

    The structure of La0,5Ca0,5MnO3 is well known for T> 250 K and T( 150 K. But in the intermediate region some structure characteristics are difficult to understand [1]. This Letter studies in this temperature region the interrelation between structure and the experimental data like magnetism and resistivity on the basis of a vibron-electron dynamic equilibrium hypothesis. It has been shown that behavior of paramagnetic-to-ferromagnetic transition can be explaned in the framework of this hypothesis.

  • 40. Wang, Bing
    et al.
    Aihara, Kazuyuki
    Kim, Beom Jun
    KTH, School of Computer Science and Communication (CSC), Computational Biology, CB.
    Comparison of immunization strategies in geographical networks2009In: Physics Letters A, ISSN 0375-9601, E-ISSN 1873-2429, Vol. 373, no 42, p. 3877-3882Article in journal (Refereed)
    Abstract [en]

    The epidemic spread and immunizations in geographically embedded scale-free (SF) and Watts-Strogatz (WS) networks are numerically investigated. We make a realistic assumption that it takes time which we call the detection time. for a vertex to be identified as infected, and implement two different immunization strategies: one is based on connection neighbors (CN) of the infected vertex with the exact information of the network structure utilized and the other is based on spatial neighbors (SN) with only geographical distances taken into account. We find that the decrease of the detection time is crucial for a successful immunization in general. Simulation results show that for both SF networks and WS networks, the SN strategy always performs better than the CN strategy. especially for more heterogeneous SF networks at long detection time. The observation is verified by checking the number of the infected nodes being immunized. We found that in geographical space, the distance preferences in the network construction process and the geographically decaying infection rate are key factors that make the SN immunization strategy outperforms the CN strategy. It indicates that even in the absence of the full knowledge of network connectivity we can still stop the epidemic spread efficiently only by using geographical information as in the SN strategy. which may have potential applications for preventing the real epidemic spread.

  • 41. Weady, S.
    et al.
    Agarwal, S.
    Wilen, L.
    Wettlaufer, John S.
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Yale University, New Haven, United States.
    Circuit bounds on stochastic transport in the Lorenz equations2018In: Physics Letters A, ISSN 0375-9601, E-ISSN 1873-2429, Vol. 382, no 26, p. 1731-1737Article in journal (Refereed)
    Abstract [en]

    In turbulent Rayleigh–Bénard convection one seeks the relationship between the heat transport, captured by the Nusselt number, and the temperature drop across the convecting layer, captured by the Rayleigh number. In experiments, one measures the Nusselt number for a given Rayleigh number, and the question of how close that value is to the maximal transport is a key prediction of variational fluid mechanics in the form of an upper bound. The Lorenz equations have traditionally been studied as a simplified model of turbulent Rayleigh–Bénard convection, and hence it is natural to investigate their upper bounds, which has previously been done numerically and analytically, but they are not as easily accessible in an experimental context. Here we describe a specially built circuit that is the experimental analogue of the Lorenz equations and compare its output to the recently determined upper bounds of the stochastic Lorenz equations [1]. The circuit is substantially more efficient than computational solutions, and hence we can more easily examine the system. Because of offsets that appear naturally in the circuit, we are motivated to study unique bifurcation phenomena that arise as a result. Namely, for a given Rayleigh number, we find a reentrant behavior of the transport on noise amplitude and this varies with Rayleigh number passing from the homoclinic to the Hopf bifurcation.

  • 42. Xiao, S. S.
    et al.
    Qiu, Min
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Study of transmission properties for waveguide bends by use of a circular photonic crystal2005In: Physics Letters A, ISSN 0375-9601, E-ISSN 1873-2429, Vol. 340, no 06-maj, p. 474-479Article in journal (Refereed)
    Abstract [en]

    We study the transmission properties for the waveguide bends composed by a circular photonic crystal. Two types (Y and U type) of the waveguide bends utilizing the circular photonic crystal are studied. It has been shown, compared with the conventional photonic crystal waveguide bends, transmission properties for these bends can be significantly improved. Over a 6.4% bandwidth, less than 1-dB loss/bend are observed. U bent waveguide, i.e., 180 degrees bend, can be easily realized with low loss using the circular photonic crystal.

  • 43. Xiao, S. S.
    et al.
    Shen, L. F.
    He, Sailing
    KTH, Superseded Departments, Electromagnetic Theory.
    A plane-wave expansion method based on the effective medium theory for calculating the band structure of a two-dimensional photonic crystal2003In: Physics Letters A, ISSN 0375-9601, E-ISSN 1873-2429, Vol. 313, no 01-2, p. 132-138Article in journal (Refereed)
  • 44. Yang, Zongxian
    et al.
    Lu, Zhansheng
    Luo, Gaixia
    Hermansson, Kersti
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Oxygen vacancy formation energy at the Pd/CeO2(111) interface2007In: Physics Letters A, ISSN 0375-9601, E-ISSN 1873-2429, Vol. 369, no 02-jan, p. 132-139Article in journal (Refereed)
    Abstract [en]

    The atomic and electronic structure of Pd adsorption on the unreduced and reduced ceria (111) surfaces is studied using first principles projector-augmented-wave (PAW) method based density functional theory (DFT) within generalized gradient approximation (GGA) and with the inclusion of on-site Coulomb interaction (GGA + U). It is found that there exist different adsorption features for Pd on different surfaces (unreduced and reduced): (1) on the unreduced CeO2(111) surface, Pd prefers to be adsorbed on the O-bridge site (O-2-site); (2) on the reduced CeO2(111) surface, the adsorption is much stronger than that on the unreduced CeO2(111) surface; (3) the formation of an oxygen vacancy is easier at the Pd/CeO2(111) interface than that on the clean CeO2(111) surface, indicating that the Pd adatom enhances the oxygen storage capacity (OSC) of ceria, and the interaction between the palladium catalyst and the ceria support enhances the lower temperature activity of the catalyst. The mechanisms for this promotion in the OSC of ceria at the Pd/ceria interface are discussed.

  • 45. Zhu, Jun
    et al.
    Zhao, Hang
    Qiu, Min
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Surface waves on the relativistic quantum plasma half-space2013In: Physics Letters A, ISSN 0375-9601, E-ISSN 1873-2429, Vol. 377, no 28-30, p. 1736-1739Article in journal (Refereed)
    Abstract [en]

    We present a theoretical investigation on the propagation of surface waves on the relativistic quantum plasma half-space. The dispersion relations of surface plasmon polaritons (SPPs) and electrostatic surface waves containing relativistic quantum corrected terms are derived. Results show that the frequency of SPPs has a blue-shift, and surface Langmuir oscillations can propagate on the cold plasma half-space due to quantum effects. Numerical evaluation indicates that quantum effects to SPPs and electrostatic surface waves are significant and observable.

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