scholarly journals Plasma Theory of Solar Radar Echoes after Thirty Years

2002 ◽  
Vol 12 ◽  
pp. 389
Author(s):  
Valentin Mel’nik
Keyword(s):  
Cross Sections ◽  
Isotropic Turbulence ◽  
Radar Signal ◽  
The Sun ◽  
Langmuir Turbulence ◽  
Radar Echoes ◽  
Radar Scattering ◽  
Plasma Theory ◽  
High Level

In 1967 Gordon made the revolutionary assumption that reflection of radar signal from the Sun can be explained by its scattering on microturbulence (Gordon 1973). In his first model it was ion-sound turbulence. Later he considered radar scattering on Langmuir turbulence. The principal opportunity to explain frequency displacements of radar echoes observed in James’ experiments (James 1966, 1970) was shown. However, it turned out (Gerasimova 1979) that the mechanism needed an impermissible high level of isotropic turbulence for the reflection with cross-sectionsσ= 10πR2ʘ.

scholarly journals Interpretation of James' Experiments in Plasma Theory of Solar Radar Echoes

2002 ◽  
Vol 199 ◽  
pp. 434-436
Author(s):  
V.N. Mel'nik
Keyword(s):  
Cross Sections ◽  
Radar Signal ◽  
Type Iii ◽  
Scattering Cross ◽  
The Earth ◽  
Radar Echoes ◽  
Radar Scattering ◽  
Plasma Theory ◽  
Radar Wave ◽  
Scattering Cross Sections

In the framework of the plasma theory of solar radar echoes results of the known James' experiments such as the values of effective cross-sections, the anisotropy of reflections, the spectrum of reflected signals, the heights of radar scattering and others are explained. In particular in this theory reflection of radar signal with high effective cross-sections (σ = (10 − 100)πR2⊙) occur in processes t + l ⇌ t + l on the Langmuir turbulance generated by Type III electrons at altitudes (1.4—1.6)-R⊙ when electron streams propagate towards the Earth. If the electrons move away from the Earth then the scattering cross-sections due to process t + l ⇌ t + l are small (σ < πR2⊙). Reflections from the heights up to 5R⊙ can occur at scattering of radar wave on the ion-sound turbulance (processes t + s ⇌ t) accompanied the Langmuir turbulance.

scholarly journals Simplified and Accurate Stiffness of a Prismatic Anisotropic Thin-Walled Box

2018 ◽  
Vol 12 (1) ◽  
pp. 1-20 ◽  
Author(s):  
Giacomo Canale ◽  
Felice Rubino ◽  
Paul M. Weaver ◽  
Roberto Citarella ◽  
Angelo Maligno
Keyword(s):  
Cross Sections ◽  
Torsional Stiffness ◽  
Element Analysis ◽  
Cross Sectional ◽  
Analysis And Design ◽  
Proposed Model ◽  
Vertical Walls ◽  
Thin Walled ◽  
High Level ◽  
Realistic Geometries

Background:Beam models have been proven effective in the preliminary analysis and design of aerospace structures. Accurate cross sectional stiffness constants are however needed, especially when dealing with bending, torsion and bend-twist coupling deformations. Several models have been proposed in the literature, even recently, but a lack of precision may be found when dealing with a high level of anisotropy and different lay-ups.Objective:A simplified analytical model is proposed to evaluate bending and torsional stiffness of a prismatic, anisotropic, thin-walled box. The proposed model is an extension of the model proposed by Lemanski and Weaver for the evaluation of the bend-twist coupling constant.Methods:Bending and torsional stiffness are derived analytically by using physical reasoning and by applying bending and torsional stiffness mathematic definition. Unitary deformations have been applied when evaluation forces and moments arising on the cross section.Results:Good accuracy has been obtained for structures with different geometries and lay-ups. The model has been validated with respect to finite element analysis. Numerical results are commented upon and compared with other models presented in literature.Conclusion:For cross sections with a high level of anisotropy, the accuracy of the proposed formulation is within 2% for bending stiffness and 6% for torsional stiffness. The percentage of error is further reduced for more realistic geometries and lay-ups.The proposed formulation gives accurate results for different dimensions and length rations of horizontal and vertical walls.

Solar Flux and Molecular Absorption

1999 ◽  
Author(s):  
Yuk L. Yung ◽  
William B. DeMore
Keyword(s):  
Energy Source ◽  
Solar Wind ◽  
Cross Sections ◽  
Electronic Excitation ◽  
Extreme Ultraviolet ◽  
Resonance Scattering ◽  
Planetary Atmospheres ◽  
The Sun ◽  
Atoms And Molecules ◽  
Planetary Rotation

In this book we are concerned primarily with disequilibrium chemistry, of which the sun is the principal driving force. The sun is not, however, the only source of disequilibrium chemistry in the solar system. We briefly discuss other minor energy sources such as the solar wind, starlight, precipitation of energetic particles, and lightning. Note that these sources are not independent. For example, the ultimate energy source of the magnetospheric particles is the solar wind and planetary rotation; the energy source for lightning is atmospheric winds powered by solar irradiance. Only starlight and galactic cosmic rays are completely independent of the sun. While the sun is the energy source, the atoms and molecules in the planetary atmospheres are the receivers of this energy. For atoms the interaction with radiation results in three possibilities: (a) resonance scattering, (b) absorption followed by fluorescence, and (c) ionization. lonization usually requires photons in the extreme ultraviolet. The interaction between molecules and the radiation field is more complicated. In addition to the above (including Rayleigh and Raman scattering) we can have (d) dissociation, (e) intramolecular conversion, and (f) vibrational and rotational excitation. Note that processes (a)-(e) involve electronic excitation; process (f) usually involves infrared radiation that is not energetic enough to cause electronic excitation. The last process is important for the thermal budget of the atmosphere, a subject that is not pursued in this book. Scattering and fluorescence are a source of airglow and aurorae and provide valuable tools for monitoring detailed atomic and molecular processes in the atmosphere. Processes (c) and (d) are most important for determining the chemical composition of planetary atmospheres. Interesting chemical reactions are initiated when the absorption of solar energy leads to ionization or the breaking of chemical bonds. In this chapter we provide a survey of the absorption cross sections of selected atoms and molecules. The selection is based on the likely importance of these species in planetary atmospheres.

scholarly journals The role of spin–orbit effects in the mobility of N+ ions moving in a helium gas at low temperature

2020 ◽  
Vol 74 (7) ◽  
Author(s):  
Lamia Aïssaoui ◽  
Peter J. Knowles ◽  
Moncef Bouledroua
Keyword(s):  
Low Temperature ◽  
Cross Sections ◽  
Orbit Coupling ◽  
Spin Orbit Coupling ◽  
Spin Orbit ◽  
Temperature Model ◽  
Helium Gas ◽  
Spin Orbit Interactions ◽  
High Level

Abstract The mobility of N+ ions in ground-state helium gas at very low temperature is examined with explicit inclusion of spin–orbit coupling effects. The ionic kinetics is treated theoretically with the three-temperature model. The N+–He interaction potentials, including spin–orbit coupling, are determined using high-level ab initio calculations. Then, the classical and quantal transport cross sections, both needed in the computation of the mobility coefficients, are calculated in terms of the collisional energy of the N+–He system. The numerical results, at temperature 4.3 K, show the spin–orbit interactions have negligible effect on the mobility coefficients. Graphical abstract

Radar Echoes from the Sun

1964 ◽  
Vol 8 (3) ◽  
pp. 210-225 ◽  
Author(s):  
Jesse C. James
Keyword(s):  
The Sun ◽  
Radar Echoes

The Effects of Cathodic Reagent Concentration and Small Solution Volumes on the Corrosion of Copper in Dilute Nitric Acid Solutions

CORROSION ◽  
10.5006/2655 ◽  
2017 ◽  
Vol 74 (3) ◽  
pp. 326-336 ◽  
Author(s):  
J. Turnbull ◽  
R. Szukalo ◽  
M. Behazin ◽  
D. Hall ◽  
D. Zagidulin ◽  
...  
Keyword(s):  
Nitric Acid ◽  
Cross Sections ◽  
Focused Ion Beam ◽  
Ion Beam ◽  
Exposure Period ◽  
Geologic Repository ◽  
Small Solution ◽  
High Level Nuclear Waste ◽  
Nitrate And Nitrite ◽  
High Level

The exposure conditions experienced by copper-coated high-level nuclear waste containers in a deep geologic repository will evolve with time. An early exposure period involving the gamma irradiation of aerated humid vapor could lead to the formation of nitric acid condensed in limited volumes of water on the container surface. The evolution of the corrosion processes under these conditions have been studied using pH measurements in limited volumes of water containing various concentrations of nitric acid. The extent and morphology of corrosion was examined using scanning electron microscopy on surfaces and on focused ion beam cut cross sections. The composition of corrosion products was determined by energy dispersive x-ray analyses and Raman spectroscopy. In the absence of dissolved oxygen only minor corrosion was observed with the reduction of nitric acid inhibited by the formation of either chemisorbed nitrate and nitrite species or the formation of a thin cuprite (Cu2O) layer. When the solution was aerated, both oxygen and nitric acid acted as cathodic reagents. After extensive exposure periods corrosion was stifled by the formation of corrosion product deposits of Cu2O, CuO (tenorite), and Cu2NO3(OH)3 (rouaite).

scholarly journals Encounters involving planetary systems in birth environments: the significant role of binaries

2020 ◽  
Vol 499 (1) ◽  
pp. 1212-1225
Author(s):  
Daohai Li ◽  
Alexander J Mustill ◽  
Melvyn B Davies
Keyword(s):  
Solar System ◽  
Significant Role ◽  
Cross Sections ◽  
Binary Stars ◽  
Open Cluster ◽  
Planetary Systems ◽  
The Sun ◽  
Crowded Environments ◽  
Stellar Density

ABSTRACT Most stars form in a clustered environment. Both single and binary stars will sometimes encounter planetary systems in such crowded environments. Encounter rates for binaries may be larger than for single stars, even for binary fractions as low as 10–20 per cent. In this work, we investigate scatterings between a Sun–Jupiter pair and both binary and single stars as in young clusters. We first perform a set of simulations of encounters involving wide ranges of binaries and single stars, finding that wider binaries have larger cross-sections for the planet’s ejection. Secondly, we consider such scatterings in a realistic population, drawing parameters for the binaries and single stars from the observed population. The scattering outcomes are diverse, including ejection, capture/exchange, and collision. The binaries are more effective than single stars by a factor of several or more in causing the planet’s ejection and collision. Hence, in a cluster, as long as the binary fraction is larger than about 10 per cent, the binaries will dominate the scatterings in terms of these two outcomes. For an open cluster of a stellar density 50 pc−3, a lifetime 100 Myr, and a binary fraction 0.5, we estimate that Jupiters of the order of 1 per cent are ejected, 0.1 per cent collide with a star, 0.1 per cent change ownership, and 10 per cent of the Sun–Jupiter pairs acquire a stellar companion during scatterings. These companions are typically thousands of au distant and in half of the cases (so 5 per cent of all Sun–Jupiter pairs), they can excite the planet’s orbit through Kozai–Lidov mechanism before being stripped by later encounters. Our result suggests that the Solar system may have once had a companion in its birth cluster.

scholarly journals A brief review of the intensity of lines 3C and 3D in neon-like Fe XVII

2008 ◽  
Vol 86 (1) ◽  
pp. 199-208 ◽  
Author(s):  
G V Brown
Keyword(s):  
Electron Beam ◽  
Cross Sections ◽  
Ion Trap ◽  
Diagnostic Utility ◽  
The Sun ◽  
Model Calculations ◽  
Atomic Theory ◽  
X Ray ◽  
Electron Beam Ion Trap ◽  
Intercombination Line

X-ray emission from neon-like Fe XVII has been measured with high-resolution spectrometers from laboratory or celestial sources for nearly seven decades. Two of the strongest lines regularly identified in these spectra are the 1P1 → 1S0 resonance and the 3D1 → 1S0 intercombination line, known as 3C and 3D, respectively. This paper gives a brief overview of measurements of the intensities of the lines 3C and 3D from laboratory and celestial sources and their comparison to model calculations, with an emphasis on measurements completed using an electron beam ion trap. It includes a discussion of the measured absolute cross sections compared with results from modern atomic theory calculations as well as the diagnostic utility of the relative intensity, R = I3C/I3CD, as it applies to the interpretation of spectra measured from the Sun and extra-solar sources. PACS Nos.: 32.30.Rj, 32.30.–r, 32.70.Cs, 52.72.+v, 95.85.Nv, 96.60.P–, 97.10.Ex

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