Showing papers by "David S. Cannell published in 1997"
TL;DR: A new method for characterizing particles in turbid media by cross correlating the scattered intensity fluctuations at two nearby points in the far field, which relies on single-scattering speckle being physically larger than multiple-scattered speckles.
Abstract: We describe a new method for characterizing particles in turbid media by cross correlating the scattered intensity fluctuations at two nearby points in the far field. The cross-correlation function selectively emphasizes single scattering over multiple scattering. The usual dynamic light-scattering capability of inferring particle size from decay rate is thus extended to samples that are so turbid as to be visually opaque. The method relies on single-scattering speckle being physically larger than multiple-scattering speckle. With a suitable optical geometry to select nearby points in the far field or equivalently slightly different scattering wave vectors (of the same magnitude), the multiple-scattering contribution to the cross-correlation function may be reduced and in some cases rendered insignificant. Experimental results demonstrating the feasibility of this approach are presented.
56 citations
TL;DR: A general-purpose, multifunction light-scattering instrument has been developed at the NASA Lewis Research Center for Space Shuttle and Space Station colloid crystallization and other microgravity experiments and program challenges and flight results from the STS-83 Space Shuttle mission are discussed.
Abstract: A general-purpose, multifunction light-scattering instrument has been
developed at the NASA Lewis Research Center for Space Shuttle and Space
Station colloid crystallization and other microgravity experiments. For a
single sample, the instrument can measure two-dimensional Bragg scattering
from 0.5° to 60°, dynamic and static light scattering from 10° to
170°, the shear modulus of samples before and after crystallization, and
digital color images of the sample. A carousel positions any one of eight 3-ml
samples into the test position for separate experiments. Program challenges
and flight results from the STS-83 Space Shuttle mission are
discussed.
22 citations
Patent•
04 Aug 1997
TL;DR: In this paper, a method and apparatus for analyzing a fluid containing light scattering components is described, which includes a laser adapted to direct abeam of light into the fluid such as a liquid containing particles, and at least two detectors to receive light scattered by the fluid, which received light is used to calculate a physical property of the fluid.
Abstract: A method and apparatus for analyzing a fluid containing light scattering components. The apparatus includes a laser adapted to direct abeam of light into the fluid such as a liquid containing particles, and at least two detectors to receive light scattered by the fluid, which received light is used to calculate a physical property of the fluid. A focusing lens may be used to focus the light beam to a focal waist in the fluid to enhance the degree of spatial coherence of the scattered light. The two detectors are aligned onto the focal waist and are adapted to send a signal to a data processor which correlates the signal received from said two detectors. The two detectors are spaced a substantially equal distance from the focal waist and are oriented at substantially the same angle with respect to the direction of propagation of the incident beam. The data processor is adapted to cross-correlate the signals received from the two detectors. A polarizer can be positioned between the focal waist and the two detectors to aid in positioning the detectors and to enhance the efficiency and speed of the measurement.
18 citations
TL;DR: In this article, the authors present experimental results for pattern formation in Rayleigh-B\'enard convection of a fluid with a Prandtl number \ensuremath{\sigma}\ensureMath{\simeq}4, showing that the spiral-defect-chaos (SDC) attractor has become unstable.
Abstract: We present experimental results for pattern formation in the Rayleigh-B\'enard convection of a fluid with a Prandtl number \ensuremath{\sigma}\ensuremath{\simeq}4. We find that the spiral-defect-chaos (SDC) attractor, which exists for \ensuremath{\sigma}\ensuremath{\simeq}1, has become unstable. Gradually increasing the temperature difference \ensuremath{\Delta}T from below to well above its critical value \ensuremath{\Delta}${\mathrm{T}}_{\mathrm{c}}$ no longer leads to SDC. A sudden jump of \ensuremath{\Delta}T from below to above \ensuremath{\Delta}${\mathrm{T}}_{\mathrm{c}}$ causes convection to grow from fluctuations and does yield SDC. However, the SDC is a transient; it coarsens and forms a single cell-filling spiral which then drifts toward the cell wall and disappears.
14 citations
TL;DR: In this article, the authors describe the results of experiments investigating the growth dynamics of domains which form spontaneously in a portion of the one-phase region of a binary fluid mixture in the presence of quenched disorder.
Abstract: We describe the results of experiments investigating the growth dynamics of domains which form spontaneously in a portion of the one-phase region of a binary fluid mixture in the presence of quenched disorder. Dilute silica gels imbibed with mixtures of isobutyric acid and water were pressure quenched from an equilibrium one-phase state to a region of the phase diagram lying within the coexistence curve of the pure, or gel-free, system, but outside the coexistence curve of the gel-mixture system. Small-angle light-scattering measurements revealed a ring of scattered light which appeared at large scattering wave vectors and evolved to smaller scattering wave vectors in a manner consistent with ${t}^{1/3}$ domain growth; no evidence of domain pinning was observed during the first 1000 s following a quench. Furthermore, most measurements were consistent with dynamic scaling behavior. An unexpected feature of this system was the rapid growth of long-wavelength fluctuations immediately following the quench.
8 citations
01 Jan 1997
TL;DR: In this paper, a simple single beam, laser light scattering technique was proposed which discriminates against multiple scattering in turbid media using cross-correlation of the scattered intensity at slightly different spatial positions.
Abstract: We present a simple, single beam, laser light scattering technique which discriminates against multiple scattering in turbid media using cross-correlation of the scattered intensity at slightly different spatial positions. Experimental results obtained at a scattering angle of 90° for colloidal suspensions of various concentrations show that the technique yields information on particle diameter, even for samples which are visually opaque.
5 citations
01 Jan 1997
TL;DR: There is an additional k-independent response which is observed at very early times following the quench, which is unlike the behavior of the pure system.
Abstract: We present results of experiments designed to investigate a novel domain state occurring in a binary fluid mixture when imbibed in dilute silica gel. This state occurs near the coexistence curve of the pure binary mixture (in the absence of gel), but above the coexistence curve of the binary mixture/gel system. The growth rate of the domains is proportional to t 1/3 and most measurements are consistent with dynamic scaling. However, there is an additional k-independent response which is observed at very early times following the quench, which is unlike the behavior of the pure system.