Open Access. Powered by Scholars. Published by Universities.®
Articles 1 - 9 of 9
Full-Text Articles in Physics
Excitation Efficiency Of A Morphology-Dependent Resonance By A Focused Gaussian Beam, James A. Lock
Excitation Efficiency Of A Morphology-Dependent Resonance By A Focused Gaussian Beam, James A. Lock
Physics Faculty Publications
The excitation efficiency of a morphology-dependent resonance (MDR) by an incident beam is defined as the fraction of the beam power channeled into the MDR. The efficiency is calculated for a focused Gaussian beam of arbitrary width incident on either a spherical particle or a cylindrical fiber located at an arbitrary position in the plane of the beam waist. In each case a simple formula for the efficiency is derived by use of the localized approximation for the beam-shape coefficients in the partial-wave expansion of the beam. The physical interpretation of the efficiency formulas is also discussed. (C) 1998 Optical …
Relaxational Mode Structure For Optical Probe Diffusion In High Molecular Weight Hydroxypropylcellulose, Kiril A. Streletzky, George D.J. Phillies
Relaxational Mode Structure For Optical Probe Diffusion In High Molecular Weight Hydroxypropylcellulose, Kiril A. Streletzky, George D.J. Phillies
Physics Faculty Publications
We studied translational diffusion of dilute monodisperse spheres (diameters 14 < d < 455 nm) in aqueous 1 MDa hydroxypropylcellulose (0 ≤ c ≤ 7 g/L) at 25°C using quasielastic light scattering. Spectra are highly bimodal. The two spectral modes (“slow,” “fast”) have different physical properties. Probe behavior differs between small (d < Rh) and large (d ≥ Rg) probes; Rh and Rg are the matrix polymer hydrodynamic radius and the radius of gyration, respectively. We examined the dependences of spectral lineshape parameters on d, c, scattering vector q, and viscosity η for all four probe-size and mode-type combinations. We find three time scale-separated modes: (1) a large-probe slow mode has properties characteristic of particle motion in a viscous medium; (2) a large-probe fast mode and small-probe slow modes share the same time scale, and have properties characteristic of probe motion coupled to internal chain dynamics; and (3) a small-probe fast mode has properties that can be attributed to the probe sampling local chain relaxations. In the analysis, we also attempted to apply the coupling/scaling (CS) model of Ngai and Phillies [Ngai, K. L., Phillies, G. D. J. J. Chem. Phys.,105, 8385 (1996)] to analyze our data. We find that the second mode is described by the coupling/scaling model for probe diffusion; the first and third modes do not follow the predictions of this model.
Development Of A Generalized Theoretical Model For The Response Of A Phase/Doppler Measurement System To Arbitrarily Oriented Fibers Illuminated By Gaussian Beams, Scott A. Schaub, James A. Lock, Amir A. Naqwi
Development Of A Generalized Theoretical Model For The Response Of A Phase/Doppler Measurement System To Arbitrarily Oriented Fibers Illuminated By Gaussian Beams, Scott A. Schaub, James A. Lock, Amir A. Naqwi
Physics Faculty Publications
We present a generalized theoretical model for the response of the phase/Doppler (P/D) measurement system to light scattered by cylindrical fibers. This theoretical model is valid for arbitrary fiber diameters and refractive indices, for Gaussian incident beams, and it accounts for arbitrary fiber orientations, fiber positions, and effects that are due to the two-dimensional receivers. The generalized P/D computer model (GPDCM) is the extension of an earlier study by the authors, combining past P/D simulation methodology with recent developments in modeling light scattering by tilted cylindrical fibers. A FORTRAN computer program that implements the GPDCM theoretical development was written and …
Comment On A Critique Of The Instantaneous Normal Mode (Inm) Approach To Diffusion, T. Keyes, Wu Xiong Li, Ulrich Zurcher
Comment On A Critique Of The Instantaneous Normal Mode (Inm) Approach To Diffusion, T. Keyes, Wu Xiong Li, Ulrich Zurcher
Physics Faculty Publications
A critique of the instantaneous normal mode (INM) theory of diffusion by Gezelter, Rabani, and Berne (GRB) [J. Chem. Phys. 107, 4618 (1997)] is analyzed. GRB assert that imaginary-frequency INM are corrupted with modes unrelated to barrier crossing, that proposals for removing such nondiffusive (ND) modes are inadequate, and thus that INM cannot be used to predict the self-diffusion constant, D. In rebuttal it is argued that Lennard-Jones, the system studied by GRB, is anamolously rich in ND modes. INM in molecular liquids are shown to behave as excellent indicators of barrier crossing. Even in LJ ND-INM, while plentiful, do …
Spiral Morphology-Dependent Resonances In An Optical Fiber: Effects Of Fiber Tilt And Focused Gaussian Beam Illumination, Andrew W. Poon, Richard K. Chang, James A. Lock
Spiral Morphology-Dependent Resonances In An Optical Fiber: Effects Of Fiber Tilt And Focused Gaussian Beam Illumination, Andrew W. Poon, Richard K. Chang, James A. Lock
Physics Faculty Publications
Spiral morphology-dependent resonances have been observed in a tilted optical fiber. The polarization-preserving and the cross-polarized elastic-scattering spectra for plane-wave illumination show that the wavelengths of the resonances are blueshifted quadratically as the fiber tilt angle increases. When a focused Gaussian beam illuminates the fiber at its edge, the resonances are blueshifted and broadened as the detector is offset from the scattering plane with the maximum scattering intensity. The blueshift with focused beam illumination is also a consequence of the spiral resonances. (C) 1998 Optical Society of America.
Translational Diffusion Of Small And Large Mesoscopic Probes In Hydroxypropylcellulose-Water In The Solutionlike Regime, Kiril A. Streletzky, George D.J. Phillies
Translational Diffusion Of Small And Large Mesoscopic Probes In Hydroxypropylcellulose-Water In The Solutionlike Regime, Kiril A. Streletzky, George D.J. Phillies
Physics Faculty Publications
Quasi-elastic light scattering spectroscopy was used to study the translational diffusion of monodisperse spheres in aqueous 1 MDa hydroxypropylcellulose (HPC) at 25 °C. Probe diameters d spanned 14–455 nm; HPC concentrations were 0⩽c⩽7g/L. Light scattering spectroscopy consistently found spectra having the form g(1)(t)=(1−Af)exp(−θtβ)+Af exp(−θftβf). Here θf and βf refer to the “fast” mode; θ and β describe the “slow” mode. We examine the dependence of θ, β, θf, βf, and Af on d, c, scattering vector q, and viscosity η. β=1 for large probes; elsewise, β and βf are ∈(0,1). The slow mode, with short-lived memory function, is diffusive; for …
Ray Theory Analysis Of The Shadow Blister Effect, James A. Lock
Ray Theory Analysis Of The Shadow Blister Effect, James A. Lock
Physics Faculty Publications
When an extended light source such as the Sun illuminates two objects so that their shadows lie close to each other, the shadow of one of the objects occasionally appears to bulge out toward the shadow of the other. This effect is caused by the overlap of the penumbras of the shadows and is analyzed here with ray theory. A laboratory demonstration of this phenomenon is performed and compared with theoretical predictions. (C) 1998 Optical Society of America.
Rainbow Scattering By A Cylinder With A Nearly Elliptical Cross Section, Charles L. Adler, James A. Lock, Bradley R. Stone
Rainbow Scattering By A Cylinder With A Nearly Elliptical Cross Section, Charles L. Adler, James A. Lock, Bradley R. Stone
Physics Faculty Publications
We both theoretically and experimentally examine the behavior of the first-and the second-order rainbows produced by a normally illuminated glass rod, which has a nearly elliptical cross section, as it is rotated about its major axis. We decompose the measured rainbow angle, taken as a function of the rod's rotation angle, into a Fourier series and find that the rod's refractive index, average ellipticity, and deviation from ellipticity are encoded primarily in the m = 0, 2, 3 Fourier coefficients, respectively. We determine these parameters for our glass rod and, where possible, compare them with independent measurements. We find that …
Amplification Of High-Order Rainbows Of A Cylinder With An Elliptical Cross Section, James A. Lock, Charles L. Adler, Bradley R. Stone, Patrick D. Zajak
Amplification Of High-Order Rainbows Of A Cylinder With An Elliptical Cross Section, James A. Lock, Charles L. Adler, Bradley R. Stone, Patrick D. Zajak
Physics Faculty Publications
The intensity of high-order rainbows for normally incident light and certain rotation angles of a cylinder with an elliptical cross section is greatly amplified with respect to the intensity for a circular cross-sectional cylinder. The amplification is due to a number of the internal reflections occurring past the critical angle for total internal reflection, and the effect is especially strong for odd-order rainbows, beginning with the third order. Experimentally, the fourth-and the fifth-order rainbows of a nearly elliptical cross-sectional glass rod were observed and analyzed. (C) 1998 Optical Society of America.