Nonlinear acousto-electric transport in a two-dimensional electron system

We study both theoretically and experimentally the nonlinear interaction between an intense surface acoustic wave and a two-dimensional electron plasma in semiconductor-piezocrystal hybrid structures. The experiments on hybrid systems exhibit strongly nonlinear acousto-electric effects. The plasma turns into moving electron stripes, the acousto-electric current reaches its maximum, and the sound absorption strongly decreases. To describe the nonlinear phenomena, we develop a coupled-amplitude method for a two-dimensional system in the strongly nonlinear regime of interaction. At low electron densities the absorption coefficient decreases with increasing sound intensity, whereas at high electron density the absorption coefficient is not a monotonous function of the sound intensity. High-harmonic generation coefficients as a function of the sound intensity have a nontrivial behavior. Theory and experiment are found to be in a good agreement.Comment: 27 pages, 6 figure

Socioeconomic development and changing reasons for using desert kites to kill gazelles

Possible reasons for using kites to kill gazelles are comprehensively reviewed in this article. Even though they are now well inventoried and documented, desert kites are still not well understood, as exemplified by the recurrent controversies about their function and dating. According to the dominant view, kites were hunting structures used to drive and to mass kill large herds of wild ungulates, particularly gazelles. Although kites were intensively used during the Early Bronze Age, some of them could have been built and used before that. Beyond these issues, the cultural and socioeconomic aspects of the kites phenomenon are even less understood, and therefore, we focus on changing reasons for the long-lasting use of kites as hunting devices. We contend that the reasons why they were used during the period of utilization for hunting gazelles changed, in most cases, in response to socioeconomic development. It is hypothesized, for example, that, as a result of urban development, kites may have been increasingly (but not exclusively) used to kill gazelles to trade their products with urban communities and farmers, even though they had other uses as well which are also considered. The main hypothesis presented in this article enables diverse opinions about the types of uses and reasons for utilizing desert kites to be reconciled, including in particular varied reasons given in the literature about why they were used for killing gazelles