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David S. Cannell

Bio: David S. Cannell is an academic researcher from University of California, Santa Barbara. The author has contributed to research in topics: Convection & Light scattering. The author has an hindex of 40, co-authored 128 publications receiving 5921 citations. Previous affiliations of David S. Cannell include Memorial University of Newfoundland.


Papers
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01 Aug 2004
TL;DR: In this article, the results of experimental investigations of gradient driven fluctuations induced in a liquid mixture with a concentration gradient and in a single component fluid with a temperature gradient were presented, and the experimental apparatus was developed to carry out similar measurement under microgravity conditions.
Abstract: We present the results of experimental investigations of gradient driven fluctuations induced in a liquid mixture with a concentration gradient and in a single-component fluid with a temperature gradient. We also describe the experimental apparatus being developed to carry out similar measurement under microgravity conditions.

1 citations

01 Nov 1998
TL;DR: In this paper, the authors report on the kinetics of nucleation and growth extracted from time-resolved Bragg images and measurements of the elastic modulus of crystalline phases obtained by monitoring resonant responses to sinusoidal forcing through dynamic light scattering.
Abstract: The Physics of Hard Spheres Experiment (PHaSE) seeks a complete understanding of the entropically driven disorder-order transition in hard sphere colloidal dispersions. The light scattering instrument designed for flight collects Bragg and low angle light scattering in the forward direction via a CCD camera and performs conventional static and dynamic light scattering at 10-160 deg. through fiber optic cables. Here we report on the kinetics of nucleation and growth extracted from time-resolved Bragg images and measurements of the elastic modulus of crystalline phases obtained by monitoring resonant responses to sinusoidal forcing through dynamic light scattering. Preliminary analysis of the former indicates a significant difference from measurements on the ground, while the latter confirms nicely laboratory experiments with the same instrument and predictions from computer simulations.

1 citations

Journal ArticleDOI
TL;DR: This work assumes that a pattern with mirror symmetry consisting of two identical grain boundaries and otherwise straight rolls in a cylindrical cell does not rotate, and assumes that the extent of deviations of the patterns from mirror symmetry, on the same coarse-grained scale, is time independent.
Abstract: Ahlers and Cannell Respond: Folse and Mead make the interesting observation that the patterns observed by Ahlers, Cannell, and Steinberg^ rotate at a uniform rate for t ̂ 60. Here ris time measured in units of the horizontal thermal diffusion time L^/^, with t^^SJK and L=^ Rl d^ where d\\s the vertical dimension of the container of radius i?, and K is the thermal diffusivity. The original authors were aware of the fact that their patterns rotated (see Ref. 10 of Ref. 1), but they had not established the uniformity of that rotation. With the orientation B of the pattern in radians and the time I'm units of t^, we obtain 0-= d9/dl^2.0x lO\"\"\"* from the analysis of Folse and Mead. Rotation of a convective flow pattern in a circular container had been studied previously by Steinberg, Ahlers, and Cannell.^ Those authors found that rotation occurred at the uniform rate ^ = LOxlO\"\"^ for their case, but rotation ceased when a small change occurred in the pattern. This change yielded a pattern with a plane of mirror symmetry. Although more extensive experimental and theoretical studies of this problem are clearly desirable, it appears that the rotation is ''driven\" by departures of the pattern from mirror symmetry. On the basis of the observations of Steinberg, Ahlers, and Cannell, we assume that a pattern with mirror symmetry consisting of two identical grain boundaries and otherwise straight rolls in a cylindrical cell does not rotate.^ Thus we also presume that the rotation of the patterns of Ref. 1 was not strictly uniform. Whenever two nearly identical grain boundaries were established, rotation probably ceased. However, this situation prevailed only for a small fraction of the time of the experiment reported in Ref. 1. We also presume that the instantaneous rotation rate depended upon the extent of departures from mirror symmetry. However these short-time variations in 0 are not resolved by the data of Ref. 1 or the analysis of Folse and Mead. Rather, the analysis shows that the coarse-grained value of 9 which can be inferred from the experiment is constant. We therefore presume that the extent of deviations of the patterns from mirror symmetry, on the same coarse-grained scale, is time independent. We believe that this lends further support to the idea that the process involved in the time dependence reported in Ref. 1 is stationary and not relaxational.

1 citations

Journal ArticleDOI
06 Dec 2011
TL;DR: In this paper, the results of measurements of giant nonequilibrium fluctuations in a single component fluid (density fluctuations) and a mixture (concentration fluctuations) driven by applied temperature gradients, both on Earth and in space, were obtained during the September 2007 FOTON M3 mission.
Abstract: We present the results of measurements of giant nonequilibrium fluctuations in a single component fluid (density fluctuations) and a mixture (concentration fluctuations) driven by applied temperature gradients, both on Earth and in space. Flight data were obtained during the September 2007 FOTON M3 mission. Spatial power spectra obtained using the shadowgraph method, during flight, confirm that the asymptotic behaviour extends to such low wave vector q, as to be limited by the sample thickness. Quantitative comparison with theory is provided, and is generally quite good. Temporal sequences of shadowgraph images for the mixture, both on Earth and during flight will be presented to emphasize the dramatic differences. Fluctuation lifetimes of thousands of seconds were observed during flight. The rugged but sensitive shadowgraph scattering method (phase fluctuations below 10 milliradians measured to within a few percent absolute accuracy) will be described briefly.

1 citations


Cited by
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Journal ArticleDOI
TL;DR: A comprehensive review of spatiotemporal pattern formation in systems driven away from equilibrium is presented in this article, with emphasis on comparisons between theory and quantitative experiments, and a classification of patterns in terms of the characteristic wave vector q 0 and frequency ω 0 of the instability.
Abstract: A comprehensive review of spatiotemporal pattern formation in systems driven away from equilibrium is presented, with emphasis on comparisons between theory and quantitative experiments. Examples include patterns in hydrodynamic systems such as thermal convection in pure fluids and binary mixtures, Taylor-Couette flow, parametric-wave instabilities, as well as patterns in solidification fronts, nonlinear optics, oscillatory chemical reactions and excitable biological media. The theoretical starting point is usually a set of deterministic equations of motion, typically in the form of nonlinear partial differential equations. These are sometimes supplemented by stochastic terms representing thermal or instrumental noise, but for macroscopic systems and carefully designed experiments the stochastic forces are often negligible. An aim of theory is to describe solutions of the deterministic equations that are likely to be reached starting from typical initial conditions and to persist at long times. A unified description is developed, based on the linear instabilities of a homogeneous state, which leads naturally to a classification of patterns in terms of the characteristic wave vector q0 and frequency ω0 of the instability. Type Is systems (ω0=0, q0≠0) are stationary in time and periodic in space; type IIIo systems (ω0≠0, q0=0) are periodic in time and uniform in space; and type Io systems (ω0≠0, q0≠0) are periodic in both space and time. Near a continuous (or supercritical) instability, the dynamics may be accurately described via "amplitude equations," whose form is universal for each type of instability. The specifics of each system enter only through the nonuniversal coefficients. Far from the instability threshold a different universal description known as the "phase equation" may be derived, but it is restricted to slow distortions of an ideal pattern. For many systems appropriate starting equations are either not known or too complicated to analyze conveniently. It is thus useful to introduce phenomenological order-parameter models, which lead to the correct amplitude equations near threshold, and which may be solved analytically or numerically in the nonlinear regime away from the instability. The above theoretical methods are useful in analyzing "real pattern effects" such as the influence of external boundaries, or the formation and dynamics of defects in ideal structures. An important element in nonequilibrium systems is the appearance of deterministic chaos. A greal deal is known about systems with a small number of degrees of freedom displaying "temporal chaos," where the structure of the phase space can be analyzed in detail. For spatially extended systems with many degrees of freedom, on the other hand, one is dealing with spatiotemporal chaos and appropriate methods of analysis need to be developed. In addition to the general features of nonequilibrium pattern formation discussed above, detailed reviews of theoretical and experimental work on many specific systems are presented. These include Rayleigh-Benard convection in a pure fluid, convection in binary-fluid mixtures, electrohydrodynamic convection in nematic liquid crystals, Taylor-Couette flow between rotating cylinders, parametric surface waves, patterns in certain open flow systems, oscillatory chemical reactions, static and dynamic patterns in biological media, crystallization fronts, and patterns in nonlinear optics. A concluding section summarizes what has and has not been accomplished, and attempts to assess the prospects for the future.

6,145 citations

Journal ArticleDOI
TL;DR: An overview about the selection of the ingredients, different ways of SLN production and SLN applications, and the in vivo fate of the carrier are presented.

2,786 citations

Journal ArticleDOI
TL;DR: These techniques are described and illustrated with examples highlighting current capabilities and limitations of single-molecule force spectroscopy.
Abstract: Single-molecule force spectroscopy has emerged as a powerful tool to investigate the forces and motions associated with biological molecules and enzymatic activity. The most common force spectroscopy techniques are optical tweezers, magnetic tweezers and atomic force microscopy. Here we describe these techniques and illustrate them with examples highlighting current capabilities and limitations.

2,155 citations

Dissertation
01 Oct 1948
TL;DR: In this article, it was shown that a metal should be superconductive if a set of corners of a Brillouin zone is lying very near the Fermi surface, considered as a sphere, which limits the region in the momentum space completely filled with electrons.
Abstract: IN two previous notes1, Prof. Max Born and I have shown that one can obtain a theory of superconductivity by taking account of the fact that the interaction of the electrons with the ionic lattice is appreciable only near the boundaries of Brillouin zones, and particularly strong near the corners of these. This leads to the criterion that the metal should be superconductive if a set of corners of a Brillouin zone is lying very near the Fermi surface, considered as a sphere, which limits the region in the momentum space completely filled with electrons.

2,042 citations

Journal ArticleDOI
TL;DR: In this article, a review of recent developments in the hydro- dynamic stability theory of spatially developing flows pertaining to absolute/convective and local/global instability concepts is presented.
Abstract: The goal of this survey is to review recent developments in the hydro­ dynamic stability theory of spatially developing flows pertaining to absolute/convective and local/global instability concepts. We wish to dem­ onstrate how these notions can be used effectively to obtain a qualitative and quantitative description of the spatio-temporal dynamics of open shear flows, such as mixing layers, jets, wakes, boundary layers, plane Poiseuille flow, etc. In this review, we only consider open flows where fluid particles do not remain within the physical domain of interest but are advected through downstream flow boundaries. Thus, for the most part, flows in "boxes" (Rayleigh-Benard convection in finite-size cells, Taylor-Couette flow between concentric rotating cylinders, etc.) are not discussed. Further­ more, the implications of local/global and absolute/convective instability concepts for geophysical flows are only alluded to briefly. In many of the flows of interest here, the mean-velocity profile is non-

1,988 citations