Raymond J. Cronise

WEIGHTLESS BUBBLE LATTICES : A CASE OF FROTH WICKING

In the absence of gravity drainage, froth wicking draws excess fluid onto a bubble lattice. Capillary forces only cause fluid transport; a moving front moves stably and without fluid fingering along a constant velocity bubble–fluid contact line. This percolation of fluid crawling up the lattice shows (1) fluid coverage on lattice borders varies linearly with available surface area (proportional to lattice perimeter); (2) fluid accelerates through regions or nests of high bubble density (number of bubbles cm−2). The development of nearly two‐dimensional bubble lattices in variable gravity (step function between 0.01 and 1.8 times earthly gravity) are examined experimentally and a zeroth‐order model for froth wetting is presented, which captures many of the principal observations. Possible applications for bubble lattices include adhesion casting of metals and separation of biological cells, bacteria, and particles.

Computerized in vitro test for chemical toxicity based on Tetrahymena swimming patterns

An apparatus and a method for rapidly determining chemical toxicity have been evaluated as an alternative to the rabbit eye initancy test (Draize). The toxicity monitor includes an automated scoring of how motile biological cells (Tetrahymena pyriformis) slow down or otherwise change their swimming patterns in a hostile chemical environment. The method, called the Motility Assay (MA), is tested for 30 s to determine the chemical toxicity in 20 aqueous samples containing trace organics and salts. With equal or better detection limits, results compare favorably to in vivo animal tests of eye irritancy.

SELF‐ORGANIZED CRITICALITY IN CLOSED ECOSYSTEMS: CARBON DIOXIDE FLUCTUATIONS IN BIOSPHERE 2

A little understood question in climate and ecological modelling is when a system appropriately can be considered in statistical equilibrium or quasi-steady state. The answer bears on a host of central issues, including the ability of small perturbations to cause large catastrophes, the constant drift of unsettled systems, and the maximum amount of environmental control theoretically possible. Using Biosphere 2 records, the behaviour of carbon dioxide fluctuations was tested for correspondence with theories now known collectively as self-organized criticality. The signature of agreement with other large, composite systems, including forest fires, stock markets, and earthquakes, is a common frequency spectrum or power-law correlations. In this case, the large- and small-scale ends of the spectrum share a common driving force and consequently no single cut-off exists for excluding or ignoring small environmental changes. From the Biosphere 2 carbon dioxide data, the fluctuations in internal atmospheres vary in both small and large steps. The time fluctuations were examined as they varied over 2 years and over three orders of magnitude in fluctuation size, then binned into characteristic size classes. The statistics show a power-law scaling exponent of −1·3, compared with −1 for classical flicker noise (1/f spectrum) and −2·5 for analogous sand-pile experiments developed to test the predictions of a self-organized, critical system. For comparison with open ecosystems, the Byrd climatic record of global CO2 over the last 50 ka has a similar power-law relation but with −2·3 as the scaling exponent. For generalizing self-organized criticality, the design suggests that otherwise unrelated biological and physical models may share a common correlation between the frequency of small and large length-scales or equivalently exhibit temporal similarity laws. The results potentially have wide implications for environmental control in otherwise chaotic or difficult to predict ecological behaviour.

Surface plasmon resonance evaluation of colloidal silver aerogel filters

Abstract Aerogels containing silver nanoparticles were fabricated for gas catalysis applications. By applying the concept of an average or effective dielectric constant to the heterogeneous interlayer surrounding each particle, we extend the technique of immersion spectroscopy to heterogeneous or porous media. Specifically, we extend the predominant effective medium theories for the determination of the average fractional composition of each component in this inhomogeneous layer. Hence, the surface area of metal available for catalytic gas reaction is determined. The technique is satisfactory for statistically random metal particle distributions but needs modification for aggregated systems.

Preferred negative geotactic orientation in mobile cells: Tetrahymena results

For the protozoan species Tetrahymena a series of airplane experiments are reported, which varied gravity as an active laboratory parameter and tested for corresponding changes in geotaxic orientation of single cells. The airplane achieved alternating periods of low (0.01 g) and high (1.8 g; g = 980 cm/s) gravity by flying repeated Keplerian parabolas. The experimental design was undertaken to clearly distinguish gravity from competing aerodynamic and chemical gradients. In this way, each culture served as its own control, with gravity level alone determining the orientational changes. On average, 6.3% of the Tetrahymena oriented vertically in low gravity, while 27% oriented vertically in high-gravity phases. Simplified physical models are explored for describing these cell trajectories as a function of gravity, aerodynamic drag, and lift. The notable effect of gravity on turning behavior is emphasized as the biophysical cause of the observed negative geotaxis in Tetrahymena. A fundamental investigation of the biological gravity receptor (if it exists) and improved modeling for vertical migration in important types of ocean plankton motivate the present research.

Noble Metal Immersion Spectroscopy of Silica Alcogels and Aerogels

We have fabricated aerogels containing gold and silver nanoparticles for gas catalysis applications. The technique of immersion spectroscopy is extended to porous or heterogeneous media allowing the surface area of metal available for catalytic gas reaction to be determined. Specifically, we apply the predominant effective medium theories to the heterogeneous interlayer surrounding each particle to determine the average fractional composition of each component in this inhomogeneous layer. The technique is satisfactory for statistically random metal particle distributions but needs further modification for aggregated or surfactant modified systems. Additionally, the kinetics suggest that collective particle interactions in coagulated clusters are perturbed during silica gelation resulting in a change in the aggregate geometry.

Toward a benchmark material in aerogel development

Discovered in the thirties, aerogels constitute today the lightest solids known while exhibiting outstanding thermal and noise insulation properties in air and vacuum. In a far‐reaching collaboration, the Space Science Laboratory at NASA Marshall Space Flight Center and the Microstructured Materials Group at Lawrence Berkeley National Laboratory are engaged in a two‐fold research effort aiming at characterizing the microstructure of silica aerogels and the development of benchmark samples through the use of in‐orbit microgravity environment. Absence of density‐driven convection flows and sedimentation is sought to produce aerogel samples with narrow distribution of pore sizes, thus largely improving transparency of the material in the visible range. Furthermore, highly isotropic distribution of doping materials are attainable even in large gels grown in microgravity. Aerospace companies (cryogenic tanks insulation and high temperature insulation of space vehicles), insulation manufacturers (household and ...

Gravitational Effects on Closed-Cellular-Foam Microstructure

Polyurethane foam has been produced in low gravity for the first time. The cause and distribution of different void or pore sizes are elucidated from direct comparison of unit-gravity and low-gravity samples. Low gravity is found to increase the pore roundness by 17% and reduce the void size by 50%. The standard deviation for pores becomes narrower (a more homogeneous foam is produced) in low gravity. Both a Gaussian and a Weibull model fail to describe the statistical distribution of void areas, and hence the governing dynamics do not combine small voids in either a uniform or a dependent fashion to make larger voids. Instead, the void areas follow an exponential law, which effectively randomizes the production of void sizes in a nondependent fashion consistent more with single nucleation than with multiple or combining events.

Ocean-atmosphere CO2 exchange: An accessible lab simulation for considering biological effects

Phytoplankton is considered a key component mediating the ocean-atmospheric exchange of carbon dioxide and oxygen. Lab simulations which model biological responses to atmospheric change are difficult to translate into natural settings owing in part to the vertical migration of phytoplankton. In the sea this vertical migration acts to regulate actual carbon dioxide consumption. To capture some critical properties of this vertical material transfer, we monitored the effects of atmospheric CO2 on dense suspensions of bioconvecting microorganisms. Bioconvection refers to the spontaneous patterns of circulation which arise among such upwardly swimming cells as alga, protozoa, zoospore and large bacteria. Gravity, phototaxis and chemotaxis have all been implicated as affecting pattern-forming ability. The ability of a biologically active suspension to detect atmospheric changes offers a unique method to quantify organism adjustment and vertical migration. With increasing CO2, bioconvection patterns in alga (P. parva) and protozoa (T. pyriformis) lose their robustness, and surface cell populations retreat from the highest CO2 regions. Cell movement (both percent motile and mean velocity) generally diminishes. A general program of image analysis yields statistically significant variations in macroscopic migration patterns; both fractal dimension and various crystallographic parameters correlate strongly with carbon dioxide content.

Microbial diffraction gratings as optical detectors for heavy metal pollutants

As a significant industrial pollutant, cadmium is implicated as the cause of itai‐itai disease. For biological detection of cadmium toxicity, an assay device has been developed using the motile response of the protozoa species, Tetrahymena pyriformis. This mobile protozoa measures 50 μm in diameter, swims at 10 body lengths per second, and aggregates into macroscopically visible patterns at high organism concentrations. The assay demonstrates a Cd+2 sensitivity better than 1 μM and a toxicity threshold to 5 μM, thus encouraging the study of these microbial cultures as viable pollution detectors. Using two‐dimensional diffraction patterns within a Tetrahymena culture, the scattered light intensity varies with different organism densities (population counts). The resulting density profile correlates strongly with the toxic effects at very low dosages for cadmium (<5 ppm) and then for poison protection directly (with nickel and copper antagonists competing with cadmium absorption). In particular, copper dosa...