5,349 research outputs found

    Evolution of vacancy pores in bounded particles

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    In the present work, the behavior of vacancy pore inside of spherical particle is investigated. On the assumption of quasistationarity of diffusion fluxes, the nonlinear equation set was obtained analytically, that describes completely pore behavior inside of spherical particle. Limiting cases of small and large pores are considered. The comparison of numerical results with asymptotic behavior of considered limiting cases of small and large pores is discussed.Comment: 25 pages, 10 figure

    Superconducting Junctions with Ferromagnetic, Antiferromagnetic or Charge-Density-Wave Interlayers

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    Spectra and spin structures of Andreev interface states and the Josephson current are investigated theoretically in junctions between clean superconductors (SC) with ordered interlayers. The Josephson current through the ferromagnet-insulator-ferromagnet interlayer can exhibit a nonmonotonic dependence on the misorientation angle. The characteristic behavior takes place if the pi state is the equilibrium state of the junction in the particular case of parallel magnetizations. We find a novel channel of quasiparticle reflection (Q reflection) from the simplest two-sublattice antiferromagnet (AF) on a bipartite lattice. As a combined effect of Andreev and Q reflections, Andreev states arise at the AF/SC interface. When the Q reflection dominates the specular one, Andreev bound states have almost zero energy on AF/ s-wave SC interfaces, whereas they lie near the edge of the continuous spectrum for AF/d-wave SC boundaries. For an s-wave SC/AF/s-wave SC junction, the bound states are found to split and carry the supercurrent. Our analytical results are based on a novel quasiclassical approach, which applies to interfaces involving itinerant antiferromagnets. Similar effects can take place on interfaces of superconductors with charge density wave materials (CDW), including the possible d-density wave state (DDW) of the cuprates.Comment: LT24 conference proceeding, 2 pages, 1 figur

    Design of a CO2 heat pump drier with dynamic modelling tools

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    Drying is an energy and time intensive process which thermal energy demand is mostly provided by fossil resources. Especially in the food processing industry it is important to increase the energy efficiency of drying processes in terms of organic products and sustainability. The potential of using a heat pump with R744 (CO2) as a working media to provide the thermal energy was investigated for typical food drying temperature of 50 °C at a relative humidity of 20 %. A dynamic heat pumpassisted dryer model has been developed and validated. The model was created with respect to heat transfer, pressure loss and flow requirements. The simulated results showed that a closed-loop heat pump assisted drying process has the potential to reduce the energy demand by around 80 % compared to conventional open-loop drying processes with fossil resources as energy source. Furthermore, the implementation of a bypass in the air cycle was examined to further enhance the energy efficiency of the system

    Twist Defect in Chiral Photonic Structures

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    We demonstrate that twisting one part of a chiral photonic structure about its helical axis produces a single circularly polarized localized mode that gives rise to an anomalous crossover in propagation. Up to a crossover thickness, this defect results in a peak in transmission and exponential scaling of the linewidth for a circularly polarized wave with the same handedness as structure. Above the crossover, however, the linewidth saturates and the defect mode can be excited only by the oppositely polarized wave, resulting in a peak in reflection instead of transmission.Comment: 12 page

    Cosmic-ray propagation properties for an origin in SNRs

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    We have studied the impact of cosmic-ray acceleration in SNR on the spectra of cosmic-ray nuclei in the Galaxy using a series expansion of the propagation equation, which allows us to use analytical solutions for part of the problem and an efficient numerical treatment of the remaining equations and thus accurately describes the cosmic-ray propagation on small scales around their sources in three spatial dimensions and time. We found strong variations of the cosmic-ray nuclei flux by typically 20% with occasional spikes of much higher amplitude, but only minor changes in the spectral distribution. The locally measured spectra of primary cosmic rays fit well into the obtained range of possible spectra. We further showed that the spectra of the secondary element Boron show almost no variations, so that the above findings also imply significant fluctuations of the Boron-to-Carbon ratio. Therefore the commonly used method of determining CR propagation parameters by fitting secondary-to-primary ratios appears flawed on account of the variations that these ratios would show throughout the Galaxy.Comment: Accepted for publication in Ap
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