John T. Foley

Bio: John T. Foley is an academic researcher from Mississippi State University. The author has contributed to research in topics: Wavelength & Near and far field. The author has an hindex of 18, co-authored 63 publications receiving 1206 citations. Previous affiliations of John T. Foley include University of Rochester.

Frequency shifts of spectral lines produced by scattering from spatially random media

Abstract: Scattering of polychromatic light by a medium whose dielectric susceptibility is a random function of position is considered within the accuracy of the first Born approximation. It is shown, in particular, that if the two-point spatial correlation function of the dielectric susceptibility has Gaussian form and the spectrum of the incident light has a Gaussian profile, the spectrum of the scattered light may be shifted toward the shorter or the longer wavelengths, depending on the angle of scattering. The results are analogous to those derived recently in connection with radiation from partially coherent sources [ Nature (London)326, 363 ( 1987)].

Phenomenon of spectral switches as a new effect in singular optics with polychromatic light

Abstract: It is shown that the recently discovered phenomenon of so-called spectral switches has a natural interpretation in the framework of singular optics with polychromatic light and that it should be regarded as being primarily a manifestation of diffraction-induced spectral changes rather than correlation-induced spectral changes as was suggested in the original papers [the first one appearing in Opt. Commun. 162, 57 (1999)] reporting this effect.

Do evanescent waves contribute to the far field

Abstract: Evanescent waves have become of considerable interest in recent years because of developments in near-field optics. Claims have been made that such waves contribute to the radiation fields of sources and to the far fields of scatterers. We show, by considering a spherical scalar wave and a linear electric dipole field, that these claims are misleading and that such contributions are without physical consequences. Our conclusions apply to a much broader class of fields than those considered in this Letter.

Nonpropagating string excitations

Abstract: It is shown that certain force distributions applied to a finite portion of an infinitely long string do not produce any excitation outside the region of the applied force. The existence of such nonpropagating excitations is demonstrated by a simple example, and two general theorems concerning their nature are proven. Some analogies between nonpropagating string excitations and fields produced by nonradiating sources are noted.

Using recovery modalities between training sessions in elite athletes: does it help?

Abstract: Achieving an appropriate balance between training and competition stresses and recovery is important in maximising the performance of athletes. A wide range of recovery modalities are now used as integral parts of the training programmes of elite athletes to help attain this balance. This review examined the evidence available as to the efficacy of these recovery modalities in enhancing between-training session recovery in elite athletes. Recovery modalities have largely been investigated with regard to their ability to enhance the rate of blood lactate removal following high-intensity exercise or to reduce the severity and duration of exercise-induced muscle injury and delayed onset muscle soreness (DOMS). Neither of these reflects the circumstances of between-training session recovery in elite athletes. After high-intensity exercise, rest alone will return blood lactate to baseline levels well within the normal time period between the training sessions of athletes. The majority of studies examining exercise-induced muscle injury and DOMS have used untrained subjects undertaking large amounts of unfamiliar eccentric exercise. This model is unlikely to closely reflect the circumstances of elite athletes. Even without considering the above limitations, there is no substantial scientific evidence to support the use of the recovery modalities reviewed to enhance the between-training session recovery of elite athletes. Modalities reviewed were massage, active recovery, cryotherapy, contrast temperature water immersion therapy, hyperbaric oxygen therapy, nonsteroidal anti-inflammatory drugs, compression garments, stretching, electromyostimulation and combination modalities. Experimental models designed to reflect the circumstances of elite athletes are needed to further investigate the efficacy of various recovery modalities for elite athletes. Other potentially important factors associated with recovery, such as the rate of post-exercise glycogen synthesis and the role of inflammation in the recovery and adaptation process, also need to be considered in this future assessment.

The Stability of Inverse Problems

Abstract: Many inverse problems arising in optics and other fields like geophysics, medical diagnostics and remote sensing, present numerical instability: the noise affecting the data may produce arbitrarily large errors in the solutions. In other words, these problems are ill-posed in the sense of Hadamard.

Spreading of partially coherent beams in random media

Abstract: Some published computational work has suggested that partially coherent beams may be less susceptible to distortions caused by propagation through random media than fully coherent beams. In this paper this suggestion is studied quantitatively by examining the mean squared width of partially coherent beams in such media as a function of the propagation distance. The analysis indicates under what conditions, and to what extent, partially coherent beams are less affected by the medium.