Nonlocality in Homogeneous Superfluid Turbulence

Simulating superfluid turbulence using the localized induction approximation in periodic bound- aries produces open-orbit vortices, which make superfluid turbulence unsustainable. Calculating with the fully nonlocal Biot-Savart law prevents the open-orbit state from forming, but also in- creases computation time. We use a truncated Biot-Savart integral to investigate the effects of nonlocality on homogeneous turbulence. We find that including the nonlocal interaction up to the average intervortex spacing prevents this open-orbit state from forming, yielding an accurate model of homogeneous superfluid turbulence with less computation time

Vortex Simulations on a 3-Sphere

We generate vortex tangles using a Hopf flow on a 3-sphere, in place of the standard torus defined by periodic boundary conditions. These tangles are highly anisotropic, with vortices tending to align along the flow direction. Standard power law dependences change accordingly from their values in more isotropic tangles. The line length density $\langle L\rangle$ is proportional to $v_{ns}^{1.28}$, where $v_{ns}$ is the drive velocity, and the reconnection rate depends roughly on $\langle L\rangle^2$. We also discuss the effect of the full Biot-Savart law versus the local induction approximation (LIA). Under LIA the tangle collapses so that all vortices are nearly aligned with a single flow line, in sharp contrast to the torus where they become perpendicular to the driving velocity. Finally we present a few torus simulations with a helical velocity field, which in some ways resembles the 3-sphere flow

Strain analysis of multiferroic BiFeO3-CoFe2O4 nanostructures by Raman scattering

We report a Raman scattering investigation of columnar BiFeO3-CoFe2O4 (BFO-CFO) epitaxial thin film nanostructures, where BFO pillars are embedded in a CFO matrix. The feasibility of a strain analysis is illustrated through an investigation of two nanostructures with different BFO-CFO ratios. We show that the CFO matrix presents the same strain state in both nanostructures, while the strain state of the BFO pillars depends on the BFO/CFO ratio with an increasing tensile strain along the out-of-plane direction with decreasing BFO content. Our results demonstrate that Raman scattering allows monitoring strain states in complex 3D multiferroic pillar/matrix composites.Comment: revised version submitted to Appl. Phys. Let

The Production of Chloropicrin as Needed from Dry Mixtures of Picric Acid and Bleaching Powder

Chloropicrin or trichloromethane is a colorless liquid boiling at l 12°C and having a specific gravity of 1.69. It was first prepared by Stenhouse from picric acid and bleaching powder. Its first use was in chemical warfare by the Allied troops in 1918. It was prepared in large quantities at Edgewood Arsenal during the World War, by the method developed and patented by the senior author. Picric acid, hydrated lime, and water were mixed to form a calcium picrate suspension. This suspension together with a suspension of bleaching powder and water was run into a still. The chloropicrin was steam-distilled off