Электронные состояния и персистентные токи в кольцах с неоднородным спин-орбитальным взаимодействием Рашбы

The paper considers one-dimensional isolated quantum rings in a perpendicular magnetic field, in which Rashba spin-orbit coupling parameter changes along the ring. Electronic spectra and persistent currents of such ring structures are calculated for different values of the structure parameters and the magnitude of the magnetic flux. It is shown that the inhomogeneity of the Rashba parameter leads to anticrossing of energy levels and smoothing of the dependence of the persistent charge current on the flux. The influence of inhomogeneity on the spin persistent current turns out to be more significant: the projection of the spin current on the ring axis ceases to be preserved when moving along the ring; additional extrema or zeros appear on the dependence of the absolute value of the spin current on the magnetic flux for a given number of electrons in the ring.

Function of the heterocercal tail in white sturgeon: flow visualization during steady swimming and vertical maneuvering

Basal ray-finned fishes possess a heterocercal tail in which the dorsal lobe containing the extension of the vertebral column is longer than the ventral lobe. Clarifying the function of the heterocercal tail has proved elusive because of the difficulty of measuring the direction of force produced relative to body position in the aquatic medium. We measured the direction of force produced by the heterocercal tail of the white sturgeon (Acipenser transmontanus) by visualizing flow in the wake of the tail using digital particle image velocimetry (DPIV) while simultaneously recording body position and motion using high-speed video. To quantify tail function, we measured the vertical body velocity, the body angle and the path angle of the body from video recordings and the vortex ring axis angle and vortex jet angle from DPIV recordings of the wake downstream from the tail. These variables were measured for sturgeon exhibiting three swimming behaviors at 1.2 L s(−)(1), where L is total body length: rising through the water column, holding vertical position, and sinking through the water column. For vertical body velocity, body angle and path angle values, all behaviors were significantly different from one another. For vortex ring axis angle and vortex jet angle, rising and holding behavior were not significantly different from each other, but both were significantly different from sinking behavior. During steady horizontal swimming, the sturgeon tail generates a lift force relative to the path of motion but no rotational moment because the reaction force passes through the center of mass. For a rising sturgeon, the tail does not produce a lift force but causes the tail to rotate ventrally in relation to the head since the reaction force passes ventral to the center of mass. While sinking, the direction of the fluid jet produced by the tail relative to the path of motion causes a lift force to be created and causes the tail to rotate dorsally in relation to the head since the reaction force passes dorsal to the center of mass. These data provide evidence that sturgeon can actively control the direction of force produced by their tail while maneuvering through the water column because the relationship between vortex jet angle and body angle is not constant.

Seamless Fiber Metal Abradables: A New Concept in Engine Seals

Fiber metal abradable seals are used for clearance control in gas turbine engines. Abradable seals accommodate rubs between the rotating system and the engine housing. Abradable seals also block the passage of air around the rotating system. Conventional seals are fabricated in flat sheet and formed into ring shape, with a seam in the ring axis direction. Seamless seals are fabricated in ring form with no seam. For conventional fiber metal seals, the seal material properties are adjusted to best suit the requirements of particular applications. The seamless metal fiber seals offer improved knife edge abradability and air flow blockage performance compared to the conventional materials. The seamless seals respond to knife edge rub interaction in the same manner as conventional seals of 10 to 20% lower density. The seamless seal blocks air flow with approximately twice the effectiveness of conventional seals. Seamless seals are comparable in cost to conventional seals.