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  • 1.
    Nordebo, Sven
    Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för fysik och elektroteknik (IFE).
    On the interpretation and significance of the fluctuation-dissipation theorem in infrared spectroscopy2024Inngår i: Results in Optics, ISSN 2666-9501, Vol. 14, artikkel-id 100612Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this paper we revisit the classical fluctuation–dissipation theorem with derivations and interpretations based on quantum electrodynamics (QED). As a starting point we take the widely cited semiclassical expression of the theorem connecting the absorption coefficient with the correlation spectra of a radiating molecular dipole. The literature is suggesting how this connection can be derived in terms of quantum mechanical statistical averages, but the corresponding results in terms of QED seems to be very difficult to trace in detail. The problem is therefore addressed here based on first principles. Interestingly, it turns out that the QED approach applied to the aforementioned statistical averages does not only prove the validity of the fluctuation–dissipation theorem, but it also provides a derivation and a quantum mechanical interpretation of Schwarzschild’s equation for radiative transfer. In particular, it is found that the classical Beer–Bouguer–Lambert law is due to absorption as well as of stimulated emission, and furthermore that the source term in Schwarzschild’s equation (Kirchhoff’s law) is due solely to spontaneous emission. The significance of the fluctuation–dissipation theorem is finally elaborated on in terms of the appropriate scaling of line strength parameters (including line mixing) which is relevant in far infrared and millimeter wave broadband applications.

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  • 2.
    Nordebo, Sven
    Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för fysik och elektroteknik (IFE).
    A modified projection approach to line mixing2023Inngår i: Journal of Quantitative Spectroscopy and Radiative Transfer, ISSN 0022-4073, E-ISSN 1879-1352, Vol. 310, artikkel-id 108731Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper presents a simple approach to combine the high-resolution narrowband features of some desired isolated line models together with the far wing behavior of the projection based strong collision (SC) method to line mixing which was introduced by Bulanin, Dokuchaev, Tonkov and Filippov. The method can be viewed in terms of a small diagonal perturbation of the SC relaxation matrix providing the required narrowband accuracy close to the line centers at the same time as the SC line coupling transfer rates are retained and can be optimally scaled to thermalize the radiator after impact. The method can conveniently be placed in the framework of the Boltzmann–Liouville transport equation where a rigorous diagonalization of the line mixing problem requires that molecular phase and velocity changes are assumed to be uncorrelated. A detailed analysis for the general Doppler case is given based on the first order Rosenkranz approximation, and which also provides the possibility to incorporate quadratically speed dependent parameters. Exact solutions for pure pressure broadening and explicit Rosenkranz approximations are given in the case with velocity independent parameters (line frequency, strength, width and shift) which can readily be retrieved from databases such as HITRAN for a large number of species. Numerical examples including comparisons to published measured data are provided in two specific cases concerning the absorption of carbon dioxide in its infrared band of asymmetric stretching, as well as of atmospheric water vapor and oxygen in relevant millimeter bands.

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  • 3.
    Nordebo, Sven
    Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för fysik och elektroteknik (IFE).
    Uniform error bounds for fast calculation of approximate Voigt profiles2021Inngår i: Journal of Quantitative Spectroscopy and Radiative Transfer, ISSN 0022-4073, E-ISSN 1879-1352, Vol. 270, artikkel-id 107715Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper presents uniform error bounds for fast calculation of approximate Voigt profiles that can be useful with the computationally demanding broadband line-by-line analysis of radiative transfer in the atmosphere. Formal proofs are given and rigorous criteria are provided to determine the domain on which the Voigt profile can be approximated by the Lorentz profile within any required accuracy. The most accurate Voigt-implementation to date can then be used to determine the required threshold parameters. Since most of the broadband radiative transfer calculations in the atmosphere will pertain to far wing computations, the potential saving in time is almost the same as by replacing the Voigt computation for the Lorentzian altogether completely. The error bounds can furthermore be used to derive a simple and efficient subband adaptive line selection strategy which can be used to rigorously exclude lines that will contribute to the resulting absorption coefficient less than any given threshold.

  • 4.
    Nordebo, Sven
    et al.
    Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för fysik och elektroteknik (IFE).
    Naeem, Farhan
    Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för fysik och elektroteknik (IFE).
    Tans, Pieter
    NOAA Global Monitoring Laboratory, USA.
    Estimating the short-time rate of change in the trend of the Keeling curve2020Inngår i: Scientific Reports, E-ISSN 2045-2322, Vol. 10, s. 1-11, artikkel-id 21222Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    What exactly is the short-time rate of change (growth rate) in the trend of CO2 data such as the Keeling curve? The answer to this question will obviously depend very much on the duration in time over which the trend has been defined, as well as the smoothing technique that has been used. As an estimate of the short-time rate of change we propose to employ a very simple and robust definition of the trend based on a centered 1-year sliding data window for averaging and a corresponding centered 1-year difference (2-year data window) to estimate its rate of change. In this paper, we show that this simple strategy applied to weekly data of the Keeling curve (1974–2020) gives an estimated rate of change which is perfectly consistent with a more sophisticated regression analysis technique based on Taylor and Fourier series expansions. From a statistical analysis of the regression model and by using the Cramér–Rao lower bound, it is demonstrated that the relative error in the estimated rate of change is less than 5 %%. As an illustration, the estimates are finally compared to some other publicly available data regarding anthropogenic CO2 emissions and natural phenomena such as the El Niño.

  • 5.
    Nordebo, Sven
    et al.
    Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för fysik och elektroteknik (IFE).
    Gustafsson, Mats
    Lund University, Sweden.
    Ivanenko, Yevhen
    Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för fysik och elektroteknik (IFE).
    On the optical theorem and optimal extinction, scattering and absorption in lossy media2020Inngår i: 14th European Conference on Antennas and Propagation, EuCAP, 15 - 20 March 2020 Copenhagen, Denmark, IEEE, 2020, s. 1-5Konferansepaper (Fagfellevurdert)
    Abstract [en]

    This paper reformulates and extends some recent analytical results concerning a new optical theorem and the associated physical bounds on absorption in lossy media. The analysis is valid for any linear scatterer (such as an antenna), consisting of arbitrary materials (bianisotropic, etc.)  and arbitrary geometries,  as long as the scatterer is circumscribed by a spherical volume embedded in a lossy background medium. The corresponding formulas are here reformulated and extended to encompass magnetic as well as dielectric background media. Explicit derivations, formulas and discussions are also given for the corresponding bounds on scattering and extinction. A numerical example concerning the optimal microwave absorption and scattering in atmospheric oxygen in the 60 GHz communication band is included to illustrate the theory.

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