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Biomedical subjects

H A Stone

Publications and source records attributed to H A Stone.

At least 19 recordsLinked to original sources
PubMed2006

Coalescence of spreading droplets on a wettable substrate.

We investigate experimentally and theoretically the coalescence dynamics of two spreading droplets on a highly wettable substrate. Upon contact, surface tension drives a rapid motion perpendicular to the line of centers that joins the drops and lowers the total surface area. We find that the width of the growing meniscus bridge between the two droplets exhibits power-law behavior, growing at early times as t1/2. Moreover, the growth rate is highly sensitive to both the radii and heights of the droplets at contact, scaling as ho3/2/Ro. This size dependence differs significantly from the behavior of freely suspended droplets, in which the coalescence growth rate depends only weakly on the droplet size. We demonstrate that the scaling behavior is consistent with a model in which the growth of the meniscus bridge is governed by the viscously hindered flux from the droplets.

Journal Article↗
PubMed2005

Monodisperse double emulsions generated from a microcapillary device.

Double emulsions are highly structured fluids consisting of emulsion drops that contain smaller droplets inside. Although double emulsions are potentially of commercial value, traditional fabrication by means of two emulsification steps leads to very ill-controlled structuring. Using a microcapillary device, we fabricated double emulsions that contained a single internal droplet in a core-shell geometry. We show that the droplet size can be quantitatively predicted from the flow profiles of the fluids. The double emulsions were used to generate encapsulation structures by manipulating the properties of the fluid that makes up the shell. The high degree of control afforded by this method and the completely separate fluid streams make this a flexible and promising technique.

Journal Article↗
PubMed2004

Foam drainage on the microscale II. Imaging flow through single Plateau borders.

The liquid in foam forms an interconnected network, which is composed of Plateau borders, nodes, and films. One of the dominant pathways for foam drainage is flow through Plateau borders, and we use confocal microscopy to obtain experimental results for the flow fields inside individual Plateau borders. For three types of surfactants detailed comparisons are made with a model based upon the influence of surface viscosity at free boundaries between the gas in the bubbles and the liquid in the Plateau borders. The model describes the flows well, and we find good agreement between the surface viscosity predicted by this model and representative values found in the literature. We also give a qualitative description of the flow in the nodes.

Journal Article↗
PubMed2004

Foam drainage on the microscale I. Modeling flow through single Plateau borders.

The drainage of liquid through a foam involves flow in channels, also called Plateau borders, which generally are long and slender. We model this flow by assuming the flow is unidirectional, the shear is transverse to the flow direction, and the liquid/gas interfaces are mobile and characterized by a Newtonian surface viscosity, which does not depend on the shear rate. Numerical finite difference simulations are performed, and analytical approximations for the velocity fields inside the channels and the films that separate the bubbles are given. We compare the liquid flow rates through interior channels, exterior channels (i.e., channels contacting container walls) and films. We find that when the number of exterior channels is comparable to the number of interior channels, i.e., narrow container geometries, the exterior channels can significantly affect the dynamics of the drainage process. Even for highly mobile interfaces, the films do not significantly contribute to the drainage process, unless the amount of liquid in the films is within a factor of ten of the amount of liquid in the channels.

Journal Article↗
PubMed2004

Geometrically mediated breakup of drops in microfluidic devices.

Microfluidic technology offers capabilities for the precise handling of small fluid volumes dispersed as droplets. To fully exploit this potential requires simultaneous generation of multiple size droplets. We demonstrate two methods for passively breaking larger drops into precisely controlled daughter drops using pressure-driven flow in simple microfluidic configurations: (i) a T junction and (ii) flow past isolated obstacles. We quantify conditions for breakup at a T junction and illustrate sequential breakup at T junctions for making small drops at high dispersed phase volume fractions.

Journal Article↗
PubMed2002

Ordered clusters and dynamical states of particles in a vibrated fluid.

Fluid-mediated interactions between particles in a vibrating fluid lead to both long range attraction and short range repulsion. The resulting patterns include hexagonally ordered microcrystallites, time-periodic structures, and chaotic fluctuating patterns with complex dynamics. A model based on streaming flow gives a good quantitative account of the attractive part of the interaction.

Journal Article↗
PubMed2001

Pressure-driven laminar flow in tangential microchannels: an elastomeric microfluidic switch.

This paper describes laminar fluid flow through a three-dimensional elastomeric microstructure formed by two microfluidic channels, fabricated in layers that contact one another face-to-face (typically at a 90 degree angle), with the fluid flows in tangential contact. There are two ways to control fluid flow through these tangentially connected microchannels. First, the flow profiles through the crossings are sensitive to the aspect ratio of the channels; the flow can be controlled by applying external pressure and changing this aspect ratio. Second, the flow direction of an individual laminar stream in multiphase laminar flow depends on the lateral position of the stream within the channel; this position can be controlled by injecting additional streams of fluid into the channel. We describe two microfluidic switches based on these two ways for controlling fluid flow through tangential microchannels and present theoretical arguments that explain the observed dependence of the flow profiles on the aspect ratio of the channels.

Journal Article↗
PubMed2001

Dynamic, self-assembled aggregates of magnetized, millimeter-sized objects rotating at the liquid-air interface: macroscopic, two-dimensional classical artificial atoms and molecules.

This paper describes self-assembly of millimeter-sized, magnetized disks floating on a liquid-air interface, and rotating under the influence of a rotating external magnetic field. Spinning of the disks results in hydrodynamic repulsion between them, while the rotating magnetic field produces an average confining potential acting on all disks. The interplay between hydrodynamic and magnetic interactions leads to the formation of patterns. Theoretical analysis of hydrodynamic and magnetic forces indicates that the interactions in this system are similar to those acting in systems of finite numbers of particles behaving classically ("classical artificial atoms"). Macroscopic artificial atoms and molecules are described, and the rules governing their morphologies outlined.

Journal Article↗
PubMed2001

Dynamics of coarsening foams: accelerated and self-limiting drainage.

The evolution of a foam is determined by drainage flow of the continuous (liquid) phase and coarsening (aging) of the dispersed phase (gas bubbles). Free-drainage experiments with slow- and fast-coarsening gases show markedly different dynamics and elucidate the importance of the coupling of the two effects. Strong coarsening leads to drainage times that are shorter (accelerated drainage) and independent of the initial liquid content (self-limiting drainage). A model incorporating the physics of both drainage and diffusive coarsening shows quantitative agreement with experiment.

Journal Article↗
PubMed2001

Convection, heaping, and cracking in vertically vibrated granular slurries.

We address the situation in which vibration is applied to thin layers of granular material with water filling the pore space, but with air above. Beyond a critical drive parameter we observe heap-shaped convecting domains of nontrivial topology, which exhibit cracks as the forcing amplitude is further increased. We summarize these results in a phase diagram, understand the onset of the convecting heaps as a manifestation of the Rayleigh-Taylor instability for fluids, and measure the response of isolated convecting structures.

Journal Article↗
PubMed2001

An accurate von Neumann's law for three-dimensional foams.

The diffusive coarsening of 2D soap froths is governed by von Neumann's law. A statistical version of this law for dry 3D foams has long been conjectured. A new derivation, based on a theorem by Minkowski, yields an explicit analytical von Neumann's law in 3D which is in very good agreement with detailed simulations and experiments. The average growth rate of a bubble with F faces is shown to be proportional to F1/2 for large F, in contrast to the conjectured linear dependence. Accounting for foam disorder in the model further improves the agreement with data.

Journal Article↗
PubMed1983

Resistance to a malignant lymphoma in chickens is mapped to subregion of major histocompatibility (B) complex.

A genetic recombinant within the major histocompatibility (B) complex of the chicken has revealed the chromosomal subregion effecting resistance to Marek's disease--a malignant lymphoma induced by a herpesvirus. The recombinant, BF21-G19, occurred spontaneously among the progeny of a male heterozygous for resistant BF21-G21 and susceptible BF19-G19 haplotypes. Exposure to Marek's disease of families segregating for the recombinant showed that this new F-G arrangement conferred a level of resistance equivalent to that of the resistant parental haplotype. Thus, a gene, or genes, within or closely linked to the B-F region of the B complex appears to be responsible for the observed resistance to Marek's disease.

Animals↗
PubMed1981

Immune response and disease resistance in chickens. I. Selection for high and low titer to Salmonella pullorum antigen.

A selection experiment for high and low anti-Salmonella pullorum antibody titer was carried out over four generations within the B1B1 blood group genotype in chickens. The study was aimed primarily at identifying different response patterns controlled by immune response genes linked to the B system, the major histocompatibility complex of the chicken. Maximal divergence was obtained in the third generation of selection when agglutination titers of 1/320 and 1/80 in B1B1 high and low responders, respectively, were reached. Immune response of S. pullorum was deduced to be controlled by polygenes. The B1B1 population, selected for high immune response to S. pullorum antigen, consistently had greater total mortality as well as greater susceptibility to challenge with Marek's disease virus compared with B1B1 population selected for low response. This, however, is believed to be a consequence of random drift of genes for disease resistance in the relatively small populations and not a direct consequence of selection for high or low S. pullorum titer.

Aging↗
PubMed1979

Reliability of Arrhenius Equation in predicting vitamin A stability in multivitamin tablets.

Shelflife predictions of vitamin A stability in multivitamin tablets were calculated based on data obtained from the analyses of six multivitamin tablet preparations by the classical Arrhenius treatment. This approach gave excessive variation in the predictions. The same data were treated by a modified Arrhenius method, which reduced the variation. Long-term room temperature data show that incorrect slopes were predicted in three of the six sets of data with the modified approach. The data indicate that erroneous predictions can result when applying the Arrhenius treatment to accelerated data and that this approach should be used with extreme caution in establishing the expiration date of a multivitamin tablet product, especially where the limiting ingredient for expiration dating is a preprocessed raw material and not a single-entity chemical.

Drug Combinations↗
PubMed1977

Marek's disease: effects of B histocompatibility alloalleles in resistant and susceptible chicken lines.

Lines of chickens selected from a common ancestral population for either resistance or susceptibility to Marek's disease developed contrasting frequencies of particular B alloalleles. Comparison of inoculated sibs in backcross-families revealed that the B alloalleles characterizing the two lines accounted for an eightfold difference in tumor incidence. This genetic difference in tumorigenesis associated with the alloalleles of the major histocompatibility complex is probably expressed through the cell-mediated immune system.

Animals↗
PubMed1975

Low oncogenic potential of avian endogenous RNA tumor virus infection or expression.

Of chickens either spontaneously producing or exogenously infected in ovo with Rous-associated virus, type O (RAV-O), an endogenous virus of the chicken, only 1 died with lymphoid leukosis (LL), the most common neoplasm associated with the leukosis-sarcoma virus group. Because the chickens were not kept in strict isolation, it could not be assumed that the one LL was induced by RAV-O. In contrast, RAV-1-infected chickens from the same lines had a high incidence of LL and other neoplasms. Over 800 chickens of several inbred lines were maintained in plastic isolators free of exogenous avian leukosis-sarcoma virus infection for from 500 to nearly 1,000 days of age. No LL was observed, even though some lines are known to produce RAV-O spontaneously or to express inherited gs antigen. Three neoplasms of unknown etiology were observed, but none generally associated with leukosis virus infection. We concluded that avian endogenous virus expression had little, if any, oncogenic potential, and that exogenous avian leukosis viruses were responsible for most naturally occurring neoplasms.

Animals↗