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Analytic Return-Stroke Transmission-Line Model
Published in Robert L. Gardner, Lightning Electromagnetics, 2017
It is clear that there is room for theoretical and experimental study of coronal phenomena. The studies of Book and Price (1976) and Book (1978) inferred but did not directly observe corona. The inferred corona were of a few centimeters radius, two orders of magnitude smaller than the expected corona radius for lightning. Such a corona might be directly observed with holographic interferometry. A ruby laser used as part of a Mach-Zehnder interferometry would give electron number density through the usual Abel-inversion of the fringe shift as a function of radius. Such information would be valuable since the references cited note discrepancies between inferred coronal radius and that expected from equivalence of (4). In fact, Book and Price (1976) suggests such a model underestimates the coronal radius, while Book (1978) suggests it overestimates the radius. Direct measurement of charge densities, as discussed above, could clear this up and pave the way for a theory of coronal discharges which include time-dependence and nonideal effects such as finite-drift velocities.
Explosive Flows: Shock Tubes and Blast Waves
Published in Wen-Jei Yang, Handbook of Flow Visualization, 2018
Interferometry is the most accurate flow visualization method to determine the density of a gas in a shock-wave flow, since the fringe shift is directly related to the density. At one time, interferometry required the use of a Mach-Zehnder type of system [53, 54], which was expensive and required skilled adjustment [6, 8, 9, 55, 56]. In recent years the development of high-speed holography has greatly simplified the applicability of this technique [57–72]. Figure 5 shows an infinite-fringe interferogram made using such a double-exposure holographic method, in which the fringes trace the lines of constant refractive index and thus the isopycnics, since in most flows it may be assumed that the Gladstone–Dale constant does not change [73, 74].
Mach–Zehnder Shearing Optical Holographic Interferometry with Regulated Sensitivity
Published in Gregory R. Toker, Holographic Interferometry, 2017
One of the specific measuring problems that occur in compressible aerodynamics is discontinuous data caused by a step change of the fringe shift, ΔNsh, across a shock wave. This problem can be handled only if ΔNsh can be accurately estimated8 by introducing some complementary information. This information can be obtained from experimental data or from a computational fluid dynamics (CFD) experiment. In Reference [70], a method of avoiding ambiguity in the interpretation of interferograms near a shock is proposed. The method is based on the continuity of the double-exposure Schlieren method and holographic interferometry. In the CFD technique, the calculated errors of ΔNsh may be appreciable owing to both a severe bow shock and a high sensitivity of interference measurements. In the case of shearing interferometry, the step change of the fringe shift ΔNsh across a shock can be expressed by the following relation (compared with Equation [5.4]): () ΔNsh(x,y)=1λ∫z2z1Δn(x,y,z)dz
Soret separation of species in a salt solution under varying transient thermal field: an interferometric study through sensitivity analysis
Published in Experimental Heat Transfer, 2021
Yogesh M. Nimdeo, Atul Srivastava
In a Mach–Zehnder interferometer, test beam passing through the medium in a test cell with evolving thermal diffusion process and interfere with reference beam carrying phase information about initial boundary condition of uniform temperature distribution in the reference cell. Due to the phase difference in two beams, the interference pattern appears on the screen with successive dark and bright fringes. It is a representation of interference of crest and trough of the two light waves. Therefore, every time, the difference between temperature corresponding to the phase change of two consecutive fringes in an interferogram remains constant until the light-bending effect through the diffusion cell is considered to be negligible. It also infers that a fringe is an isotherm of constant phase, concentration, or temperature. In the case of single-wavelength interferometry, the change in temperature per fringe shift within thermal diffusion time where the temperature is the only parameter changing with time can be written as [24]