Biomedical subjects

GW Crabtree

Publications and source records attributed to GW Crabtree.

At least 19 recordsLinked to original sources

PubMed2000

Vortex flow and transverse flux screening at the bose glass transition

We study the vortex phase diagram in untwinned YBCO crystals with columnar defects. These randomly distributed defects are expected to induce a "Bose glass" phase of localized vortices exhibiting a vanishing resistance and Meissner effect for magnetic fields H( perpendicular) transverse to the columns. We directly observe the transverse Meissner effect using a Hall probe array. As predicted, the Meissner state breaks down at temperatures T(s) that decrease linearly as H( perpendicular) increases. However, T(s) lies far below the conventional melting temperature T(m) determined by a vanishing resistivity, suggesting a regime where vortices are effectively localized even when rotated off the columnar defects.

Journal Article↗

PubMed2000

Critical points in heavy ion irradiated untwinned YBa(2)Cu3O(7-delta) crystals

The critical points in untwinned YBa(2)Cu(3)O(7-delta) crystals with dilute columnar defects are investigated. We find a convergence of a first order vortex melting line with an irreversibility line associated with the onset of the Bose glass critical regime at the lower critical point. In addition, we find that columnar defects raise the upper critical point, implying that vortex line meandering is a basic feature controlling its position.

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PubMed2000

Electrostatically driven granular media: phase transitions and coarsening

We report the experimental and theoretical study of electrostatically driven granular material. We show that the charged granular medium undergoes a hysteretic phase transition from the immobile condensed state (granular solid) to a fluidized dilated state (granular gas) with a changing applied electric field. In addition we observe a spontaneous precipitation of dense clusters from the gas phase and subsequent coarsening-coagulation of these clusters. Molecular dynamics simulations show qualitative agreement with experimental results.

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PubMed2000

Patterns in thin vibrated granular layers: interfaces, hexagons, and superoscillons

A theoretical and experimental study of patterns in vibrated granular layers is presented. An order parameter model based on the parametric Ginzburg-Landau equation is used to describe strongly nonlinear excitations including hexagons, interfaces between flat antiphase domains, and new localized objects, superoscillons. The experiments confirm the existence of superoscillons and bound states of superoscillons and interfaces. On the basis of the order parameter model we predict analytically and confirm experimentally that additional subharmonic driving results in the controlled motion of interfaces.

Journal Article↗

PubMed1996