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  • American Institute of Physics (AIP)  (7)
  • 2010-2014  (1)
  • 1985-1989  (6)
  • 1
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: In order to understand the influence of H2O on the stimulated Raman Q-branch spectra of nitrogen in combusting media, an exhaustive theoretical and experimental study has been carried out. Starting from a semiclassical model, particularly convenient at high temperature, the Q-line broadening and shifting coefficients have been calculated over a wide temperature range and for a large number of lines. Stimulated Raman Spectra (SRS) measurements have allowed us to test these calculated line broadening coefficients and thus establish the high accuracy of semiclassical values. The theoretical broadening coefficients have been inverted to deduce state-to-state rotational relaxation rates by using two types of fitting laws. A partial test of the resulting Q-branch profiles has been realized at moderate pressures leading to a discrimination between these two laws. Furthermore, the effect of rotational energy transfers on collisionally narrowed profiles at higher densities has been simulated and compared with the pure N2 case.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Numerous comparisons between predictions of the model presented in part I of this paper and experimental H2O infrared linewidths are presented. It is shown that our model, contrary to those used up to now, gives accurate results for H2O room-temperature line broadening by O2 and Ar, and for high rotational quantum-number lines by N2. First accurate experimental widths and intensities of some H2O ν2-band lines in the 400–900 K temperature range are also presented. Detailed analysis of the data demonstrates the great influence of a "resonance overtaking'' mechanism. The latter results from the modifications of both the perturber rovibrational population distribution and kinetic energy with temperature; it strongly enhances the contributions of the collision-induced rotational transitions involving significant energy jumps. This mechanism is well accounted for by our model and quantitatively explains the unusually slow decrease of some linewidths with temperature.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A semiclassical theory of asymmetric-top molecule line broadening, developed in part I of this series of papers for linear perturbers, is extended to asymmetric-top perturbers. This model has been successfully applied in part II to the broadening of H2O lines by N2, O2, and Ar. The present applications to the self-broadening of H2O infrared and Raman lines in the 300–900 K range also show the quality of the model. Due to the high electrostatic forces involved in the H2O–H2O interaction, the short-range anisotropic potential has little influence. Nevertheless, the need for a modeling of the trajectory is demonstrated, mainly in the case of high rotational quantum number lines.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A semiclassical theory of infrared linewidths in the gas, previously developed for linear molecules, is extended to asymmetric top molecules. It includes a satisfactory treatment of the close collisions and is consequently adapted to describe the temperature dependence of the linewidths, in particular in the combustion temperature range. Numerical applications to the water vapor perturbed by nitrogen, oxygen, and argon show strong different behaviors following the nature of the perturber. For oxygen and argon perturbers, the contribution of close collisions is the predominant mechanism of line broadening. The consistency of the theoretical model is evidenced by comparison with precise measurements for H2O–N2, –O2, and Ar at 300 K. Moreover, the calculated temperature dependence of the linewidths is compared with recent experimental data for H2O–Ar between 1300 and 2300 K.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 2944-2950 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Measurements of the absorption by pure CO2 in the 4.3 μm region are presented. They refer to the temperature of 291 K and densities in the 1–80 amagat range. Calculations based on the addition of Lorentzian contributions strongly overestimate the absorption since they do not account for line overlapping. The energy corrected sudden approximation (ECSA) is used to model line mixing within the impact approximation. The scaling parameters of this model are deduced from line-broadening data. This calculation strongly underestimates the absorption in the spectral region near the edges of the vibrational band, whereas it overestimates the absorption in the far wings of the lines. This is attributed to the impact approximation which does not account for the frequency dependence of the relaxation operator. This dependence is roughly determined from our results; it is in good qualitative agreement with the few corresponding available results.
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  • 6
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 88 (1988), S. 2999-3006 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The ability of available theoretical models in describing broadening mechanisms is tested for the CO2–O2, CO2–CO2, and CO2–N2 systems. It is shown that the Anderson–Tsao–Curnutte theory is inaccurate since short-range forces can contribute significantly to broadening. We use the approach of Robert and Bonamy, but the usual expansion of the atom–atom potential to the fourth order around the intermolecular distance appears insufficient at short distances for these particular systems. We propose a better representation of the radial dependence of the atom–atom potential, while keeping the previous analytical expression of the cross section. Satisfactory results are obtained for both the rotational quantum number dependence of room-temperature CO2–O2, CO2–CO2, and CO2–N2 half-widths and the evolution of CO2–N2 broadening with temperature. It is shown that the isotropic part of the potential involved in the trajectory calculation must be coherently deduced from the atom–atom interaction potential.
    Type of Medium: Electronic Resource
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  • 7
    Publication Date: 2014-06-27
    Description: The current status of the mechanical and electromagnetic design for the ICRF antenna system for W7-X is presented. Two antenna plugins are discussed: one consisting of a pair of straps with pre-matching to cover the first frequency band, 25–38 MHz, and a second one consisting of two short strap triplets to cover a frequency band around 76 MHz. This paper focusses on the two strap antenna for the lower frequency band. Power coupling of the antenna to a reference plasma profile is studied with the help of the codes TOPICA and Microwave Studio that deliver the scattering matrix needed for the optimization of the geometric parameters of the straps and antenna box. Radiation power spectra for different phasings of the two straps are obtained using the code ANTITER II and different heating scenario are discussed. The potential for heating, fast particle generation, and current drive is discussed. The problem of RF coupling through the plasma edge and of edge power deposition is summarized. Important elements of the complete ion cyclotron resonance heating system are discussed: a resonator circuit with tap feed to limit the maximum voltage in the system, and a decoupler to counterbalance the large mutual coupling between the 2 straps. The mechanical design highlights the challenges encountered with this antenna: adaptation to a large variety of plasma configurations, the limited space within the port to accommodate the necessary matching components and the watercooling needed for long pulse operation.
    Print ISSN: 1070-664X
    Electronic ISSN: 1089-7674
    Topics: Physics
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