Monte Carlo study of linear chain submonolayer structures.Application to Li/W(112)

The lattice gas model for adsorption of alkaline elements on W(112) surface is studied by Monte Carlo simulations. The model includes dipole--dipole interaction as well as long-range indirect interaction. The numerical results show that truncation of the indirect interaction even at 200$\AA$ may change a phase diagram, i.e., new phases containing domain walls might occur. It is demonstrated that a defected phase can exist at high temperatures even if it is not stable at T=0. The phase diagram for Li/W(112) is constructed and long periodic chain structures (9*1), (6*1), (4*1), (3*1), and (2*1) are found to be stable at low temperatures. Role of thermal fluctuation is discussed by comparison of Monte Carlo results with mean field approximation results.Comment: 7 pages, 7 figures, REVTe

Formation of helium spectrum in solar quiescent prominences

We present new non-LTE modelling of the helium spectrum emitted by quiescent solar prominences. The calculations are made in the frame of a one-dimensional plane-parallel slab. The physical parameters of our models are the electron temperature, the gas pressure, the slab width, the microturbulent velocity and the height above the solar surface. In this paper, we present isothermal isobaric models for a large range of temperature and pressure values. This work brings considerable improvements over the calculations of Heasley and co-workers (Heasley et al. 1974, Heasley and Milkey 1976, 1978, 1983) with the inclusion in our calculations of partial redistribution effects in the formation of the HI Lyα, Lyβ, HeI λ 584 Å and HeII λ 304 Å lines. In addition we consider detailed incident profiles for the principal transitions. The statistical equilibrium equations are solved for a 33 bound levels (HeI and HeII) plus continuum atom, and the radiative transfer equations are solved by the Feautrier method with variable Eddington factors. In this way we obtain the helium level populations and the emergent line profiles. We discuss the influence of the physical parameters on the helium level populations and on the main helium spectral lines. The effect of helium abundance in the prominence plasma is also studied. Some relations between singlet and triplet lines are given, as well as between optically thin or thick lines, HeI and HeII lines, and between the HeI λ 5876 Å and HI λ 4863 Å lines. In a future work this numerical code will be used for the diagnostic of the prominence plasma by comparing the results with SUMER observations

A model of linear chain submonolayer structures. Application to Li/W(112) and Li/Mo(112)

We propose a lattice gas model to account for linear chain structures adsorbed on (112) faces of W and Mo. The model includes a dipole-dipole interaction as well as a long-ranged indirect interaction. We have explicitly demonstrated that the periodic ground states depend on a competition between dipole-dipole and indirect interaction. The effect of temperature is studied within the molecular-field approximation. The numerical results show that for dipole-dipole interaction only, all long periodic linear chain phases are suppressed to low temperatures. However, when the long-range indirect interaction becomes important, the long-periodic linear chain phases start to fill up the phase diagram and develop a high thermal stability. Model parameters are chosen to reconstruct a sequence of long-periodic phases as observed experimentally for Li/Mo(112) and Li/W(112).Comment: RevTeX 9 pages + 5 Postscript figures (included), uses newdoc.sty (included), to be published in Surface Scienc

EVALUATION OF GAS TURBINE ENGINE ROLLER BEARING LOADS BY FINITE ELEMENT METHOD TO ADJUST BEARING DURABILITY ANALYSIS

The paper presents the comparative results of calculating the life factor of a bearing of one standard size by do¬mestic and foreign methods. In order to correct the calculated life factor, obtained by the domestic method, the paper provides the analysis of the results of calculating the roller bearing, undertaken by the finite element method. It is pre¬sented that for a roller bearing having a temperature spread, the correction in the first approximation gives an unde¬restimation of the resource in 100 times

Physics of Solar Prominences: I - Spectral Diagnostics and Non-LTE Modelling

This review paper outlines background information and covers recent advances made via the analysis of spectra and images of prominence plasma and the increased sophistication of non-LTE (ie when there is a departure from Local Thermodynamic Equilibrium) radiative transfer models. We first describe the spectral inversion techniques that have been used to infer the plasma parameters important for the general properties of the prominence plasma in both its cool core and the hotter prominence-corona transition region. We also review studies devoted to the observation of bulk motions of the prominence plasma and to the determination of prominence mass. However, a simple inversion of spectroscopic data usually fails when the lines become optically thick at certain wavelengths. Therefore, complex non-LTE models become necessary. We thus present the basics of non-LTE radiative transfer theory and the associated multi-level radiative transfer problems. The main results of one- and two-dimensional models of the prominences and their fine-structures are presented. We then discuss the energy balance in various prominence models. Finally, we outline the outstanding observational and theoretical questions, and the directions for future progress in our understanding of solar prominences.Comment: 96 pages, 37 figures, Space Science Reviews. Some figures may have a better resolution in the published version. New version reflects minor changes brought after proof editin

Fermi surface of Mo(112) and indirect interaction between adsorbed atoms

A comprehensive examination of the Fermi surface of Mo(112) is presented. The Fermi surface contours for the Mo(112) surface, obtained by density functional theory calculations, agree well with the direct observations via angle-resolved photoemission spectroscopy and indicate the existence of flattened segments in the Fermi contours perpendicular to the direction of the atomic furrows. Both the calculation and the experiment indicate significant surface weight for these states. Such flattened Fermi contours at the surface can give rise to long-range charge density waves (CDW) and long-range indirect lateral interactions, especially in the case of adsorption of electropositive atoms. When mediated by the surface electrons, exhibiting flattened Fermi contours, the oscillatory potential of the indirect interaction between adsorbed atoms decays very slowly (∼1/r) in the direction along the furrows, which can explain the formation of long-period chain structures of electropositive adsorbates on the furrowed surface of Mo(112)

New view of the occupied band structure of Mo(112)

We present a comprehensive examination of the occupied surface-weighted band structure of Mo(112) along the two high-symmetry directions of the surface Brillouin zone, both from theoretical and experimental perspectives. The band structures are found to be significantly different for the states along the two high-symmetry directions and for the states with even and odd reflection parities with respect to the mirror planes. The present study suggests the existence of a number of surface-weighted bands along both high-symmetry directions. The complexity of the band structure near the Fermi level may impose potential difficulties in experimental determination of the electron-phonon coupling parameters based on the effective mass enhancement distortion (or kink) in the energy-band dispersion, in the vicinity of the Fermi level, for several surface resonance bands of Mo(112)