Collective antiskyrmion-mediated phase transition and defect-induced melting in chiral magnetic films.

Magnetic phase transitions are a manifestation of competing interactions whose behavior is critically modified by defects and becomes even more complex when topological constraints are involved. In particular, the investigation of skyrmions and skyrmion lattices offers insight into fundamental processes of topological-charge creation and annihilation upon changing the magnetic state. Nonetheless, the exact physical mechanisms behind these phase transitions remain unresolved. Here, we show numerically that it is possible to collectively reverse the polarity of a skyrmion lattice in a field-induced first-order phase transition via a transient antiskyrmion-lattice state. We thus propose a new type of phase transformation where a skyrmion lattice inverts to another one due to topological constraints. In the presence of even a single defect, the process becomes a second-order phase transition with gradual topological-charge melting. This radical change in the system's behavior from a first-order to a second-order phase transition demonstrates that defects in real materials could prevent us from observing collective topological phenomena. We have systematically compared ultra-thin films with isotropic and anisotropic Dzyaloshinskii-Moriya interactions (DMIs), and demonstrated a nearly identical behavior for such technologically relevant interfacial systems.

The effect of cholestyramine on the faecal excretion of bile acids and neutral steroids in familial hypercholesterolaemia.

The faecal excretion of total bile acids was measured in two normal subjects and in seven patients with familial hypercholesterolaemia (four heterozygotes and three homozygotes) in the untreated state and during treatment with near-maximal doses of cholestyramine. There were no significant differences between the three groups. The increase in bile-acid excretion in response to cholestyramine was as great in the homozygotes as in the normal subjects. It is concluded that familial hypercholesterolaemia is not generally due to an inherited defect in the mechanisms for catabolizing cholesterol to bile acids.

The distribution of (14C) cholesterol in muscle and skin of Rhesus monkeys after intravenous injection.

1. The specific radioactivity of [14C]cholesterol in plasma and in serial biopsies of muscle and skin was measured in Rhesus monkeys for 156 days after a single intravenous injection of [14C]cholesterol. 2. Analysis of the specific radioactitivy-time curves in terms of a two-compartment system indicated that all the cholesterol of muscle is exchangeable with the plasma cholesterol and that local synthesis does not contribute significantly to the cholesterol in muscle. 3. Analysis of the curve for specific radioactivity of skin cholesterol suggested the presence of a small pool of cholesterol with slow turnover. A contribution to skin cholesterol from local synthesis could not be excluded.