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Introduction to Radiative Transfer
Published in John R. Howell, M. Pinar Mengüç, Kyle Daun, Robert Siegel, Thermal Radiation Heat Transfer, 2020
John R. Howell, M. Pinar Mengüç, Kyle Daun, Robert Siegel
Consider an area element on the surface of the black isothermal enclosure and an elemental blackbody within the enclosure. Some of the radiation emitted by the surface element strikes the elemental body at a random direction. All this radiation, by definition, is absorbed by the blackbody. To maintain thermal equilibrium and isotropic radiation throughout the enclosure, the radiation emitted back into the incident direction must be equal to that received. Since the body is absorbing the maximum radiation from any direction, it must be emitting the maximum in any direction. Because the radiation filling the black enclosure is isotropic, the radiation received and hence emitted in any direction by the enclosed black surface, per unit projected area normal to that direction, must be the same as that in any other direction.
Quantization of Radar Theory
Published in Maged Marghany, Automatic Detection Algorithms of Oil Spill in Radar Images, 2019
The energy of the receiving antenna signal S is a function of the backscatter and is located at the same transmit antenna. This is known as monostatic radar. In this view, the term of 4πR2 in the previous equation turns into (4π)2R4 with the additional parameter of AR in the numerator. The term AR, conversely, is the operational area of the receiving antenna and is the numerator in a ratio concerning the second 4πR2. This represents the isotropic radiation owing to a target’s radar cross-section [71–77]. Under this circumstance, Equation 5.2 can be modified as: () S=PT.τ.GT.σ.Ar(4π)2R4
Optical Absorption and Fluorescence of Nanomaterials
Published in Vladimir I. Gavrilenko, Optics of Nanomaterials, 2019
where ρ(ω) denotes the spectral energy density of the isotropic radiation field at the frequency of the transition (Planck radiation law): () ρ(ω)=2πℏ(ωc)31eℏω/kT−1.
Smart networks of autonomous in-situ soil sensors
Published in European Journal of Environmental and Civil Engineering, 2023
Xavier Chavanne, Jean-Pierre Frangi
Later, the patch has been substituted with the external whip antennas: a monopole of /4 wavelength (100 mm long with Sub Miniature A RF connector from Low Power Radio Solutions Ltd, UK) and a /2 antenna from Pycom Ltd. In spite of limited information on its characteristics the latter one is chosen as the kit, which includes a U.FL cable, is cheaper than the other external antenna with its cable. Whip antennas present a Voltage Standing Wave Ratio closer to one and higher gains, as well as more isotropic radiation pattern, than the patch antenna. Voltage Standing Wave Ratio is the ratio of maximum to minimum voltages in antenna cable and measures impedance mismatch between the two components. The closer VSWR is to one the smaller are the mismatch and transmission loss. Whip antennas are more expensive and necessitate a water-tight connection through the box wall.
Efficient transfer of inversion doublet populations in deuterated ammonia using adiabatic rapid passage
Published in Molecular Physics, 2022
S. Herbers, Y. M. Caris, S. E. J. Kuijpers, J.-U. Grabow, S. Y. T. van de Meerakker
Population transfer between two components of an inversion doublet in ND is straightforward by applying microwave radiation at a frequency near 1.6 GHz for ND or 1.4 GHz for ND, as has been routinely done in a number of previous experiments studying the trapping of high-field seeking states [12–16]. These studies achieved transfer efficiencies limited to around , which the authors state is due to the width of the applied microwave pulse and the extent of the hyperfine structure. Generally, the maximum transfer efficiencies are dictated by the specific implementation of the microwave fields and the initial beam populations. E.g. in the case of incoherent isotropic radiation, starting with a single state populated in a two-level system, the limit should be , as stimulated emission and stimulated absorption have the same probability. The remaining population in the state represents a pure loss in the desired density, and can cause severe background levels from competing collision pathways in collision experiments.
Diffusion Synthetic Acceleration for Heterogeneous Domains, Compatible with Voids
Published in Nuclear Science and Engineering, 2021
B. S. Southworth, Milan Holec, T. S. Haut
The first problem we consider is the so-called crooked pipe problem, originally introduced in Ref. 17 and discussed as a benchmark for DSA in Ref. 18. This is a steady-state test problem for thermal radiative transport with a single energy group and purely isotropic scattering throughout the domain. The domain is surrounded by vacuum, has a uniform isotropic radiation field, and has an inward isotropic source times stronger than the radiation field. In Ref. 18 the problem is introduced with two scattering cross sections. Here, we modify the domain to have five regions, shown in Fig. 1, to allow for a larger variety of heterogeneities. Scattering cross section is defined to be piecewise constant over the subdomains shown in Fig. 1, and total cross section is then defined as , where is the speed of light and is the time step of the transport solution. We use an S angular discretization with 40 angles in the quadrature set (using the symmetry in two dimensions) and a second-order DG finite element discretization of the linear spatial transport equation for each angle unless otherwise noted.