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Sökning: swepub > Umeå universitet > Marklund Mattias

  • Resultat 1-10 av 189
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1.
  • Jukimenko, Olexy, et al. (författare)
  • Counterpart of the Darrieus-Landau instability at a magnetic deflagration front
  • 2016
  • Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 93:13
  • Tidskriftsartikel (refereegranskat)abstract
    • The magnetic instability at the front of the spin avalanche in a crystal of molecular magnets is considered. This phenomenon reveals similar features with the Darrieus-Landau instability, inherent to classical combustion flame fronts. The instability growth rate and the cutoff wavelength are investigated with respect to the strength of the external magnetic field, both analytically in the limit of an infinitely thin front and numerically for finite-width fronts. The presence of quantum tunneling resonances is shown to increase the growth rate significantly, which may lead to a possible transition from deflagration to detonation regimes. Different orientations of the crystal easy axis are shown to exhibit opposite stability properties. In addition, we suggest experimental conditions that could evidence the instability and its influence on the magnetic deflagration velocity.
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2.
  • Jukimenko, Olexy, 1988-, et al. (författare)
  • Multilevel model for magnetic deflagration in nanomagnet crystals
  • 2017
  • Ingår i: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 95:17
  • Tidskriftsartikel (refereegranskat)abstract
    • We extend the existing theoretical model for determining the characteristic features of magnetic deflagration in nanomagnet crystals. For the first time, all energy levels are accounted for calculation of the the Zeeman energy, the deflagration velocity, and other parameters. It reduces the final temperature and significantly changes the propagation velocity of the spin-flipping front. We also consider the effect of a strong transverse magnetic field, and show that the latter significantly modifies the spin-state structure, leading to an uncertainty concerning the activation energy of the spin flipping. Our front velocity prediction for a crystal of Mn-12 acetate in a longitudinal magnetic field is in much better agreement with experimental data than the previous reduced-model results.
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3.
  • Valiev, Damir, et al. (författare)
  • Heating of the fuel mixture due to viscous stress ahead of accelerating flames in deflagration-to-detonation transition
  • 2008
  • Ingår i: Physics Letters A. - Amsterdam : Elsevier BV. - 0375-9601 .- 1873-2429. ; 372:27-28, s. 4850-4857
  • Tidskriftsartikel (refereegranskat)abstract
    • 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.
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4.
  • Dion, Claude, 1970-, et al. (författare)
  • Anisotropic properties of spin avalanches in crystals of nanomagnets
  • 2013
  • Ingår i: Physical Review B - Condensed Matter and Materials Physics. - : American Physical Society. - 2469-9950 .- 2469-9969 .- 1098-0121 .- 1550-235X. ; 87:1
  • Tidskriftsartikel (refereegranskat)abstract
    • Anisotropy effects for spin avalanches in crystals of nanomagnets are studied theoretically with the external magnetic field applied at an arbitrary angle to the easy axis. Starting with the Hamiltonian for a single nanomagnet in the crystal, two essential quantities characterizing spin avalanches are calculated: the activation and Zeeman energies. The calculation is performed numerically for a wide range of angles and analytical formulas are derived within the limit of small angles. The anisotropic properties of a single nanomagnet lead to anisotropic behavior of the magnetic deflagration speed. Modifications of the magnetic deflagration speed are investigated for different angles between the external magnetic field and the easy axis of the crystals. Anisotropic properties of magnetic detonation are also studied, which concern, first of all, the temperature behind the leading shock and the characteristic time of spin switching in the detonation.
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5.
  • Grönlund, Andreas, 1974-, et al. (författare)
  • Evolution of rogue waves in interacting wave systems
  • 2009
  • Ingår i: Europhysics letters. - : IOP Publishing. - 0295-5075 .- 1286-4854. ; 86:2, s. 24001-
  • Tidskriftsartikel (refereegranskat)abstract
    • Large-amplitude water waves on deep water have long been known in the seafaring community, and are the cause of great concern for, e.g., oil platform constructions. The concept of such freak waves is nowadays, thanks to satellite and radar measurements, well established within the scientific community. There are a number of important models and approaches for the theoretical description of such waves. By analyzing the scaling behavior of freak wave formation in a model of two interacting waves, described by two coupled non-linear Schrödinger equations, we show that there are two different dynamical scaling behaviors above and below a critical angle θc of the direction of the interacting waves, below which all wave systems evolve and display statistics similar to a wave system of non-interacting waves. The results equally apply to other systems described by the non-linear Schrödinger equations, and should be of interest when designing optical wave guides.
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6.
  • Marklund, Mattias, et al. (författare)
  • New quantum limits in plasmonic devices
  • 2008
  • Ingår i: Europhysics letters. - Les Ulis : EDP Sciences. - 0295-5075 .- 1286-4854. ; 84:1
  • Tidskriftsartikel (refereegranskat)abstract
    • Surface plasmon polaritons (SPPs) have recently been recognized as an important future technique for microelectronics. Such SPPs have been studied using classical theory. However, current state-of-the-art experiments are rapidly approaching nanoscales, and quantum effects can then become important. Here we study the properties of quantum SPPs at the interface between an electron quantum plasma and a dielectric material. It is shown that the effect of quantum broadening of the transition layer is most important. In particular, the damping of SPPs does not vanish even in the absence of collisional dissipation, thus posing a fundamental size limit for plasmonic devices. Consequences and applications of our results are pointed out.
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7.
  • Shukla, Nitin, et al. (författare)
  • Nonlinear electromagnetic wave equations for superdense magnetized plasmas
  • 2009
  • Ingår i: PHYSICS OF PLASMAS. - : AIP Publishing. - 1070-664X .- 1089-7674. ; 16:7
  • Tidskriftsartikel (refereegranskat)abstract
    • By using the quantum hydrodynamic and Maxwell equations, we derive the generalized nonlinear electron magnetohydrodynamic, the generalized nonlinear Hall-MHD (HMHD), and the generalized nonlinear dust HMHD equations in a self-gravitating dense magnetoplasma. Our nonlinear equations include the self-gravitating, the electromagnetic, the quantum statistical electron pressure, as well as the quantum electron tunneling and electron spin forces. They are useful for investigating a number of wave phenomena including linear and nonlinear electromagnetic waves, as well as three-dimensional electromagnetic wave turbulence spectra and structures arising from mode coupling processes at nanoscales in dense quantum magnetoplasmas.
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8.
  • Shukla, Padma, et al. (författare)
  • Wake field generation and nonlinear evolution in a magnetized electron-positron-ion plasma
  • 2008
  • Ingår i: Physics of Plasmas. - New York : AIP Publishing. - 1070-664X .- 1089-7674. ; 15:8, s. 082305-1-082305-4
  • Tidskriftsartikel (refereegranskat)abstract
    • The nonlinear propagation of a circularly polarized electromagnetic (CPEM) wave in a strongly magnetized electron-positron-ion plasma is investigated. Two coupled equations describing the interaction between a high-frequency CPEM wave and the low-frequency electrostatic wake field are derived. It is found that the generation of the wake fields partly depends on the presence of the ion species and the external magnetic field. The wake field generation in turn leads to deceleration and frequency down conversion of the electromagnetic pulse.
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9.
  • Shvartsburg, Alexander, et al. (författare)
  • Superluminal tunneling of microwaves in smoothly varying transmission lines
  • 2008
  • Ingår i: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics. - New York : American Physical Society through the American Institute of Physics. - 1063-651X .- 1095-3787. ; 78, s. 016601-1-016601-6
  • Tidskriftsartikel (refereegranskat)abstract
    • Tunneling of microwaves through a smooth barrier in a transmission line is considered. In contrast to standard wave barriers, we study the case where the dielectric permittivity is positive, and the barrier is caused by the inhomogeneous dielectric profile. It is found that reflectionless, superluminal tunneling can take place for waves with a finite spectral width. The consequences of these findings are discussed, and an experimental setup testing our predictions is proposed.
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10.
  • Stenflo, Lennart, et al. (författare)
  • Rogue waves in the atmosphere
  • 2010
  • Ingår i: JOURNAL OF PLASMA PHYSICS. - : Cambridge University Press. - 0022-3778 .- 1469-7807. ; 76, s. 293-295
  • Tidskriftsartikel (refereegranskat)abstract
    • The appearance of rogue waves is well known in oceanographics, optics, and cold matter systems. Here we show a possibility for the existence of atmospheric rogue waves.
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