Phonon Lifetime Observation in Epitaxial ScN Film with Inelastic X-Ray Scattering Spectroscopy.

Phonon-phonon scattering dominates the thermal properties in nonmetallic materials, and it directly influences device performance in applications. The understanding of the scattering has been progressing using computational approaches, and the direct and systematic observation of phonon modes that include momentum dependences is desirable. We report experimental data on the phonon dispersion curves and lifetimes in an epitaxially grown ScN film using inelastic x-ray scattering measurements. The momentum dependence of the optical phonon lifetimes is estimated from the spectral width, and the highest-energy phonon mode around the zone center is found to possess a short lifetime of 0.21 ps. A comparison with first-principles calculations shows that our observed phonon lifetimes are quantitatively explained by three-body phonon-phonon interactions.

Water transport inside a single-walled carbon nanotube driven by a temperature gradient.

In this work, by means of molecular dynamics simulations, we consider the mass transport of a water cluster inside a single-walled carbon nanotube (SWNT) with a diameter of about 1.4 nm. The influence of the non-equilibrium thermal environment on the confined water cluster has been investigated by imposing a longitudinal temperature gradient on the SWNT. It is demonstrated that the water cluster is transported with an average acceleration proportional to the temperature gradient. Additional equilibrium simulations suggest that the temperature dependence of the potential energy of the confined water is sufficient to realize the transport. In particular, for a system with a hydrophobic interface, the water-water intrinsic potential energy appears to play a dominant role. The transport simulations were also performed for a system with a junction between two different SWNTs. The results suggest that an angstrom difference in diameter may result in a large barrier for water being transported through a small diameter SWNT.

Active control of oscillatory thermocapillary convection.

Active control of oscillatory thermocapillary flow was applied in an open cylindrical container filled with silicone oil. Thermocapillary convection was driven by imposing a radial temperature gradient on a flat free surface. The control was realized by locally heating the surface at a single position using the local temperature signal at a different position fed back through a simple algorithm. Significant attenuation of the oscillation was achieved in a wide range of supercritical Marangoni numbers, with the best performance in the weakly non-linear regime. Simultaneously measuring the temperature oscillation at two positions gives us a good insight in how the control influences the whole temperature field on the free surface. Quantitative analysis was done to characterize the optimal feedback amplification and the required power.

Flexion of the knee increases the distance between the popliteal artery and the proximal tibia: MRI measurements in 15 volunteers.

We determined which angle of flexion best prevents popliteal artery injury during knee surgery. We took MRIs of the knee in the lateral position with the knee in 0 degrees, 45 degrees, 90 degrees, and 120 degrees of flexion in 15 volunteers. The shortest distance between the posterior cortex of the tibia and the popliteal artery was measured at various levels from the knee joint to 60 mm distally. At the level of the joint and 15 mm distally, the distance between the tibia and artery increased with increasing knee flexion. More distally, no significant difference was noted with increasing flexion. Flexion of the knee may minimize injury to the popliteal artery in procedures between the level of the joint and 15 mm distal to the joint.