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Biomedical subjects

J S Wettlaufer

Publications and source records attributed to J S Wettlaufer.

7 recordsLinked to original sources
PubMed2006

Growth-melt asymmetry in crystals and twelve-sided snowflakes.

It is in the lexicon of crystal growth that the shape of a growing crystal reflects the underlying microscopic architecture. Although it is known that in weakly nonequilibrium conditions the slowest growing orientations ultimately dominate the asymptotic shape, is the same true for melting? Here we observe and show theoretically that while the two-dimensional steady melt shapes of ice are bounded by six planes, these planes are not proper facets but instead are rotated 30 degrees from the prism planes of ice. Finally, the transient melting state exposes 12 apparent crystallographic planes thereby differing substantially from the transient growth state.

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PubMed2005

Classical rotational inertia of solid 4He.

The observation of reduced rotational inertia in a cell containing solid 4He has been interpreted as evidence for superfluidity of the solid. We propose an alternative explanation: slippage of the solid, due to grain boundary premelting between the solid and dense adsorbed layers at the container wall. We calculate the range of film thickness, and determine the viscosity that will account for the missing rotational inertia. Grain boundary premelting also explains inertial anomalies in an earlier study of solid helium in porous glass and indicates that the liquid is partially superfluid.

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PubMed2004

Abrupt grain boundary melting in ice.

The effect of impurities on the grain boundary melting of ice is investigated through an extension of Derjaguin-Landau-Verwey-Overbeek theory, in which we include retarded potential effects in a calculation of the full frequency-dependent van der Waals and Coulombic interactions within a grain boundary. At high dopant concentrations, the classical solutal effect dominates the melting behavior. However, depending on the amount of impurity and the surface charge density, as temperature decreases, the attractive tail of the dispersion force interaction begins to compete effectively with the repulsive screened Coulomb interaction. This leads to a film-thickness/temperature curve that changes depending on the relative strengths of these interactions and exhibits a decrease in the film thickness with increasing impurity level. More striking is the fact that at very large film thicknesses, the repulsive Coulomb interaction can be effectively screened, leading to an abrupt reduction to zero film thickness.

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PubMed2001

Shocks preempt continuous curvature divergence in interface motion.

The dichotomy between two approaches to interface motion is illustrated in the context of two-dimensional crystal growth. Analyzing singularity formation based on the curvature of the interface predicts a continuous divergence of curvature in contrast to the discrete loss of orientations predicted when the evolution is described by an equation for the two-vector of the interface. We prove that the formation of a shock in the latter approach preempts continuous curvature divergence predicted in the former approach. The results are broadly applicable to kinematic interface motion problems, and we connect them with experiments reported by Maruyama et al. [Phys. Rev. Lett. 85, 2545 (2000)].

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PubMed2001

Interfacial premelting and the thermomolecular force: thermodynamic buoyancy.

The presence of a substrate can alter the equilibrium state of another material near their common boundary. Examples include wetting and interfacial premelting. In the latter case, temperature gradients induce spatial variations in the thickness of the premelted film that reflect changes in the strength of the repulsion between the substrate and the solid. We show that the net thermomolecular force on a macroscopic substrate is equivalent to a thermodynamic buoyancy force-proportional to the mass of solid that can occupy the volume enclosed by the substrate and the temperature gradient.

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PubMed2001

Possible displacement of the climate signal in ancient ice by premelting and anomalous diffusion.

The best high-resolution records of climate over the past few hundred millennia are derived from ice cores retrieved from Greenland and Antarctica. The interpretation of these records relies on the assumption that the trace constituents used as proxies for past climate have undergone only modest post-depositional migration. Many of the constituents are soluble impurities found principally in unfrozen liquid that separates the grain boundaries in ice sheets. This phase behaviour, termed premelting, is characteristic of polycrystalline material. Here we show that premelting influences compositional diffusion in a manner that causes the advection of impurity anomalies towards warmer regions while maintaining their spatial integrity. Notwithstanding chemical reactions that might fix certain species against this prevailing transport, we find that-under conditions that resemble those encountered in the Eemian interglacial ice of central Greenland (from about 125,000 to 115,000 years ago)-impurity fluctuations may be separated from ice of the same age by as much as 50 cm. This distance is comparable to the ice thickness of the contested sudden cooling events in Eemian ice from the GRIP core.

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