Results 1 - 10 of 2034
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[en] Highlights: • High resolution L1-L2,3M Coster-Kronig spectra in Ar are obtained by electron impact. • Many features are due to the autoionizing decay of neutral doubly excited states. • Energy analysis of ejected electrons ruled out hypothesis of the state origins. - Abstract: The ejected electron spectra between 25 and 56 eV kinetic energy in Ar have been measured at several electron impact energies. When the incident energy is above the Ar 2s ionization potential the peaks due to the L1-L2,3M1 and L1-L2,3M2,3 Coster-Kronig (CK) transitions are expected to occur in this region of kinetic energy, but we observe a series of other narrow structures that overlap and sometime dominate the spectrum due to the CK transitions. These features have been attributed to the autoionizing decay of inner valence doubly excited states to the Ar + ground state.
[en] The paper presents an innovative way to improve the efficiency of solar energy. The requirements for the two components of the solar cell (the substrate material and the nature of the p-n junction) are determined. The necessity of nanotechnological preparation of the solar cell substrate is shown. The conditions under which technical silicon can be considered as a substrate are determined. A physical picture of the growth process of nanoclusters on the substrate surface based on the fundamental physical effect of self-organization of semiconductor systems is given. The least acceptable parameters of the nanocluster material are determined. The mechanism of the formation process of nanoheterogeneous structure is determined. The special role solar cell nanocomponents is revealed. (authors)
[en] The effect of vibrational excitation on reaction C+SH (v = 0–20, j = 0) → S+CH, H+CS is investigated on the excited potential energy surface of HCS(A2A″) by the quasi-classical trajectory method. The obtained reaction probability, total integral cross section (ICS), and the impact parameter show that the influence of vibration excitation presents different characteristics on different reaction channels. The vibrational state-resolved ICSs, differential cross sections as well as two-angle distribution functions P(θr), P(ϕr) of products for different vibrational quantum numbers of reactant are investigated. These results show that (i) the products have obvious forward–backward scattering feature; (ii) for different reactions, the distribution P(θr) varies with vibrational quantum number of reactant; (iii) at high vibrational excitations of the reactant, the insertion mechanism becomes apparent in this reaction, so the product molecules are more positively oriented along the positive direction of the scattering plane. Graphical abstract: .
[en] We study the charge and heat transport in a normal metal/superconductor (NS) junction of the tilted anisotropic Dirac cone material borophane, using the extended Blonder–Tinkham–Klapwijk formalism. In spite of the large mismatch in the Fermi wave vector of the normal metal and superconductor sides of the borophane NS junction, the electron–hole conversion happens with unit probability at normal incidences. Furthermore, in the heavily doped superconducting regime, for heavily doped normal borophane, the electron–hole conversion happens with unit probability, at almost any incident angle. Finding the dependence of the differential Andreev conductance on the Fermi energy and excitation energy gives us a handle to distinguish specular from retro Andreev reflection. We numerically find that, independent of the Fermi energy, the temperature dependence of the differential thermal conductance in borophane can be modelled as an inverse Gaussian function, reflecting the d-wave symmetry of the borophane superconductor. We propose a scheme for achieving negative differential thermal conductance, as a key building block of thermal circuits, at intermediate Fermi energies. Our findings will have potential applications in developing borophane-based thermal management and signal manipulation mesoscopic structures such as heat transistors, heat diodes, and thermal logic gates. (paper)
[en] The molecular R-matrix formalism is used to calculate bound and continuum states of the CH molecule. Potential energy curves for the bound states of doublet and quartet symmetry are obtained for an extended range of inter nuclear distances between 1–9 a.u. Resonance positions and widths for low-lying Feshbach resonances are also obtained for states with doublet symmetry. These resonances and their continuation as bound states below the CH+ ion ground state are used to construct dissociative states which cross the ground state of the CH+ ion. Several dissociative states of , and symmetry, that were hitherto unknown, have been found and are expected to be useful for other collisional calculations, in particular, for the dissociative recombination of the CH+ ion. (paper)
[en] We study the consequences of thermoelastic coupling on heat and stress pulse propagation along equilibrium and nonequilibrium reference states. We use a generalized heat-transport equation accounting for relaxational and nonlinear effects. We compare the obtained results with those for heat pulses without thermoelastic coupling and with previous results obtained by using the relaxational Maxwell–Cattaneo equation for the heat flux without nonlinear terms. The difference of the speed of heat pulses along and against an imposed average heat flux in nonequilibrium states is also obtained.
[en] Ultrafast wavepacket dynamics of electron-phonon-photon systems is studied by numerical calculations. When nonadiabaticity of electron-phonon systems is taken into account, Raman scattering process plays an important role in the dynamics of the system. The interplay of the electron-phonon nonadiabaticity and the Raman scattering is found to determine the wavepacket motion particularly in the vicinity of the conical intersection of adiabatic potential energy surfaces, which shows that this effect should be considered in order to reveal the photoexcitation/deexcitation process of materials in femtosecond time scale. Graphical abstract: .
[en] Ionic liquid-based nanofluids are a very novel group of fluids used for enhancing heat transfer in different applications, especially in solar energy ones where the parabolic trough pipe receiver is subjected to heat flux due to the sun beam radiation. In regard to this new class of fluids, no empirical correlations are available for their heat transfer capabilities inside tubes even if some research on local Nusselt number of regular flow is present in the current literature. This paper introduces new correlation for heat transfer and friction factor in pipes subjected to constant heat flux considering [C4mim] [NTf2] ionic liquid-based nanofluids flow. In addition, the performance evaluation criteria as an optimization parameter between heat transfer enhancement and pressure drop penalty have been evaluated. In this particular application, the flow is laminar, as recommended in low heat flux applications (solar beam radiation), with Reynolds number in the range of 100–2000 and nanoparticles volume concentration varying from 0 to 2.5%. In addition, according to the change in the [C4mim] [NTf2] ionic liquid thermophysical properties with temperature, the Prandtl number consequently has been changed. As an overall conclusion, the proposed correlations can be seen as favorable for the heat transfer enhancement estimation of the parabolic trough for the solar energy applications. Finally, this pioneering class of heat transfer fluids (ionic liquid-based nanofluids) reveals a great potential in advanced heat transfer applications; therefore, the new correlations aim to collaborate to this progress.
[en] The excitation-autoionization cross section for the 5p6 subshell in Ba atoms was determined in an incident electron energy range from the lowest autoionization threshold at 15.61 eV up to 600 eV. The data were obtained by measuring the total intensity of ejected-electron spectra arising from the decay of the 5p5n1l1n2l2n3l3 autoionizing states. The energy behavior of the cross section is characterized by the presence of a strong resonance structure in the near-threshold energy region of 15.6–22.7 eV as well as a broad maximum around 80 eV. The cross section reaches its maximum value of (3.2 ± 1.0)×10−16 cm2 at 17.4 eV, which makes out a contribution of up to 25% to the total single-ionization cross section of Ba atoms. The role of particular configurations in formation of the cross section is considered on the basis of the spectroscopic classification and excitation dynamics of the 5p5n1l1n2l2n3l3 autoionizing states. Graphical abstract: .
[en] It has been proved that dropwise condensation (DWC) has better heat transfer than filmwise condensation. DWC occurs on hydrophobic or superhydrophobic surfaces (SHS). Low surface energy and surface roughness are two key specifications of SHS. Roughness leads to appearing of Cassie and Wenzel morphologies on SHS. In the Cassie state, droplet suspends over roughness while in the Wenzel state droplets penetrates through roughness. Single Cassie droplets have higher mobility (an advantage) than Wenzel droplets while having a lower heat transfer rate (a disadvantage). The advantage of Cassie droplets leads to that droplets depart the surface at lower radius, sweep other droplets and prepare fresh surface for nucleating of new droplets. Some researchers have shown that surfaces with Wenzel droplets have better heat transfer and some have indicated that surfaces with Cassie droplets have better performance. Hence, a numerical investigation has been done in this study to explore which of these two morphologies have better performance in DWC. Results show that advantage and disadvantage of the morphologies can prevail on the other according to surface conditions. For example, a surface with Cassie state droplets may have higher or lower total heat transfer than a surface with Wenzel droplets depending on roughness height.