Results 1 - 10 of 1354
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[en] A new discrete-ordinates method for coupled electron-photon transport is presented and applied to space shielding calculations. It is found that the discrete-ordinates method is as accurate as the standard Monte Carlo method, but is much more efficient
[en] The effect of recombination centers on the relaxation process of photoexcited 2D electron systems in polar semiconductors is studied theoretically. Our analysis takes into account the most important mechanisms of relaxation. We find that under certain conditions recombination to centers can drastically modify the e-ph interaction via reduction of screening. Consequently, the time behaviour of the energy exchange rate between the electronic system and the lattice can also be altered. Our results indicate that recombination to centers affects, in different ways, the time evolution of the carrier temperature and the rate of energy exchange rate. Qualitative agreement with some experimental data lends support to the model and allows us to make some predictions. (author)
[en] A large photonic band gap (PBG) is highly favorable for photonic crystal devices. One of the most important goals of PBG materials research is identifying structural design strategies for maximizing the gap size. We provide a comprehensive analysis of the PBG properties of two-dimensional (2D) quasicrystals (QCs), where rotational symmetry, dielectric fill factor, and structural morphology were varied systematically in order to identify correlations between structure and PBG width at a given dielectric contrast (13:1, Si:air). The transverse electric (TE) and transverse magnetic (TM) PBGs of 12 types of QCs are investigated (588 structures). We discovered a 12mm QC with a 56.5% TE PBG, the largest reported TE PBG for an aperiodic crystal to date. We also report here a QC morphology comprising ''throwing star''-like dielectric domains, with near-circular air cores and interconnecting veins emanating radially around the core. This interesting morphology leads to a complete PBG of ∼20% , which is the largest reported complete PBG for aperiodic crystals.
[en] Full text: One of the important problems in multilayer thermionics is related to the thermalisation of hot electrons in the electrodes and in the barrier region. Thermalisation may occur directly via the electron-phonon interaction, or indirectly via the electron-electron interaction. In semiconductor heterostructures at room temperature, the LO phonon plays a crucial role in thermalising electrons. In this work we study the thermalisation of electrons in a single barrier structure by taking into account the electron-phonon interaction. The relaxation is dependent on the lattice temperature of each electrode. Because the rate of thermalisation increases with the temperature exponentially and thermalisation in the barrier region only affects the emission current from the hot electrode, the reduction of thermionic emission for the hot electrode is greater than that for the cold electrode. As a result, we find that the theoretical thermal efficiency can increase due to thermalisation
[en] The cross sections for the processes γν → γγ → ν anti ν are calculated with the aid of an effective Lagrangian derived from the Standard model. These cross sections are shown to be much larger than the elastic cross section σ(γν → γν) for photon energies ω ≥ 1 keV. Possible astrophysical implications are discussed
[en] Within the context of the photon-neutrino weak interaction, the temperature dependence is studied of the composite character of the photon and the critical temperature above which the particle masses vanish. The result obtained implies the existence of two temperatures: one below which gauge symmetry breaks down and photon attains an effective mass, and another above which γ5-symmetry may be restored. These may have some relevance in the study of the early Universe and also in the theories of low-temperature physics. (author)
[en] Manganese-doped ZnS nanoparticle was synthesized through a room-temperature wet-processing method. The ZnS:Mn2+ nanophosphor showed the particle size of about 4 nm, and a single phase of cubic structure compared with the bulk sample with double phases of cubic and hexagonal structures. Yellow Mn2+ emission peak showed the redshift by about 15 nm compared with the bulk sample due to the increased field strength resulting from the quantum confinement effect. Especially, with increasing temperature, the yellow emission of the nanophosphor showed the blueshift in the peak position due to the decreased field strength resulting from the lattice expansion. With increasing temperature, the yellow emission of the nanophosphor increases and then decreases. It can be described in terms of two competing factors of the thermal release of trapped charges and the phonon-electron interaction.