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Wharmby A.W.,711th Human Performance Wing | Bagley R.L.,University of Texas at San Antonio
International Journal of Engineering Science | Year: 2015

An empirical model has been recently derived and used to modify Maxwell's equations for dielectric materials based on viscoelastic analysis techniques that employs concepts from the fractional calculus. The empirical model was originally used to curve fit complex permittivity data of dielectrics exposed to electromagnetic fields oscillating in the radiofrequency band. The model was then incorporated into Maxwell's equations giving rise to a fractional order Ampere's law that subsequently produced a fractional order wave equation. This wave equation was shown to accurately describe the behavior of an electromagnetic wave propagating through a dielectric material. This work demonstrates that the application of these techniques can seamlessly be extended into the terahertz frequency band (ranging approximately from 1011 Hz to 1013 Hz) producing results of comparable accuracy to that which was shown in the radiofrequency band (ranging approximately from 102 Hz to 1010 Hz) while still remaining consistent with thermodynamic principles. The procedure is briefly reviewed and compared to the historical dielectric models of Debye and Cole-Cole and then applied to model the dielectric behavior of select materials in the terahertz frequency band. The work concludes with an analysis on the dispersion and absorption of terahertz waves using the aforementioned fractional order wave equation. Source


Williamson C.A.,UK Defence Science and Technology Laboratory | McLin L.N.,711th Human Performance Wing
Applied Optics | Year: 2015

A simple model for laser eye dazzle is presented together with calculations for laser safety applications based on the newly defined Maximum Dazzle Exposure (MDE) and Nominal Ocular Dazzle Distance (NODD). A validated intraocular scatter model has been combined with a contrast threshold target detection model to quantify the impact of laser eye dazzle on human performance. This allows the calculation of the MDE, the threshold laser irradiance below which a target can be detected, and the NODD, the minimum distance for the visual detection of a target in the presence of laser dazzle. The model is suitable for non-expert use to give an estimate of anticipated laser eye dazzle effects in a range of civilian and military scenarios. © 2015 Optical Society of America. Source


Wharmby A.W.,711th Human Performance Wing
International Journal of Engineering Science | Year: 2016

In the first paper of this series, an empirical formula based on viscoelastic analysis techniques that employs concepts from the fractional calculus originally used to model the dielectric behavior of materials exposed to oscillating electromagnetic fields in the radiofrequency band was applied to do the same for electromagnetic fields oscillating in the terahertz frequency range. The empirical formula was integrated into Maxwell's equations producing a fractional order Ampere's law whereof a fractional order wave equation was derived. This wave equation was used to describe the absorption and dispersion of terahertz waves in a dielectric medium. In this work, the empirical formula is extended again for application in the infrared frequency spectrum. The fractional calculus dielectric model is adapted to curve fit the complex refractive index data of a variety of semiconductors and insulators. Following the same procedure used in the first paper of this series, the fractional calculus dielectric model is again integrated in Maxwell's equations with the same dispersion and absorption analysis performed using the newly derived fractional order wave equation. The mathematical consequences of extending this model into infrared frequencies are also discussed. Source


Wharmby A.W.,711th Human Performance Wing | Bagley R.L.,University of Texas at San Antonio
International Journal of Engineering Science | Year: 2014

A mathematical model of viscoelasticity employing fractional order derivatives is adapted and applied to model the dielectric behavior of materials while remaining consistent with thermodynamic principles. The model is then incorporated into Maxwell's equations using techniques from viscoelasticity. The modified Maxwell's equations are found to yield a fractional order wave equation that is solved analytically and is found to remain consistent with dissipative and dispersive phenomena. Source


Walsh A.J.,National Research Council Italy | Beier H.T.,711th Human Performance Wing
Progress in Biomedical Optics and Imaging - Proceedings of SPIE | Year: 2016

Time-correlated single photon counting (TCSPC) is the most robust method for fluorescence lifetime imaging using laser scanning microscopes. However, TCSPC is inherently slow making it ineffective to capture rapid events due to the single photon product per laser pulse causing extensive acquisition time limitations and the requirement of low fluorescence emission efficiency to avoid bias of measurement towards short lifetimes. Furthermore, thousands of photons per pixel are required for traditional instrument response deconvolution and fluorescence lifetime exponential decay estimation. Instrument response deconvolution and fluorescence exponential decay estimation can be performed in several ways including iterative least squares minimization and Laguerre deconvolution. This paper compares the limitations and accuracy of these fluorescence decay analysis techniques to accurately estimate double exponential decays across many data characteristics including various lifetime values, lifetime component weights, signal-to-noise ratios, and number of photons detected. Furthermore, techniques to improve data fitting, including binning data temporally and spatially, are evaluated as methods to improve decay fits and reduce image acquisition time. Simulation results demonstrate that binning temporally to 36 or 42 time bins, improves accuracy of fits for low photon count data. Such a technique reduces the required number of photons for accurate component estimation if lifetime values are known, such as for commercial fluorescent dyes and FRET experiments, and improve imaging speed 10-fold. Copyright © 2016 SPIE. Source

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