Dynamics of electrons in the quantum Hall bubble phases

In Landau levels N > 1, the ground state of the two-dimensional electron gas (2DEG) in a perpendicular magnetic field evolves from a Wigner crystal for small filling of the partially filled Landau level, into a succession of bubble states with increasing number of guiding centers per bubble as the filling increases, to a modulated stripe state near half filling. In this work, we show that these first-order phase transitions between the bubble states lead to measurable discontinuities in several physical quantities such as the density of states and the magnetization of the 2DEG. We discuss in detail the behavior of the collective excitations of the bubble states and show that their spectra have higher-energy modes besides the pinned phonon mode. The frequencies of these modes, at small wavevector k, have a discontinuous evolution as a function of filling factor that should be measurable in, for example, microwave absorption experiments.Comment: 13 pages, 7 figures. Corrected typos in eqs. (38),(39),(40

Optimal Sizing and Cruise Speed Determination for a Solar-Powered Airplane

[[abstract]]This paper presents the use of a genetic algorithm to optimize the size and cruise speed of a solar-powered manned aerial vehicle named Xihe. A conceptual aerodynamiccon figuration design is conducted first to obtainthe initial size of the aircraft and the performance parameters. The optimization process then searches for optimal solutions for minimum energy operation. To minimize the number of decision variables, the aspect ratio of the wing and the fuselage design are fixed during optimization. The mass of the Xihe aircraft is then parameterized as a function of two performance parameters: wingreference areaandcruise speed. Withthe parameterization results, a fittness function that links the optimization problem and the genetic algorithm is then established. The genetic algorithm searches for the optimal results for minimum energy operation. This optimization process reduces the referenced wing area of the Xihe aircraft from 5:63 m2 in the conceptual design to 4:91 m2, which allows the reduction of the solar cell panel by 12.79%, reducing the costs. Optimization reduces the mass of the aircraft from 24.96 to 22.47 kg: a 9.98% reduction. The cost of the complex materials used would be less than originally required, and the cruise speed would increase from 10.93 to 11:23 m=s (the cruise speed for minimum power consumption).[[incitationindex]]SCI[[incitationindex]]EI[[booktype]]紙本[[booktype]]電子