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Recently, an electron-spin filter was proposed by depositing a nanosized ferromagnetic metal stripe and a Schottky normal metal stripe on the top of the semiconductor heterostructure [F. Zhai, H. Q. Xu and Y. Guo, Phys. Rev. B70 (2004) 085308]. This device has a considerable electron-spin polarization and potential application in spintronics. Here we apply a bias to this device and theoretically demonstrate how to manipulate its electron-spin polarization. By numerical simulations, we found that not only the amplitude of the electron-spin polarization but also its sign varies with the bias, giving rise to a bias-tunable spin filter device. [ABSTRACT FROM AUTHOR]

A Magnetoresistance device is proposed in a both magnetically and electrically modulated two-dimensional electron gas, which can be realized experimentally by the deposition, on the top and bottom of a semiconductor heterostructure, of two parallel metallic ferromagnetic strips under an applied voltage. It is shown that a considerable magnetoresistance effect can be achieved in such a device due to the significant transmission difference for electrons through parallel and antiparallel magnetization configurations. It is also shown that the magnetoresistance ratio depends strongly on the applied voltage to the stripe in the device. These interesting properties may provide an alternative scheme to realize magnetoresistance effect in hybrid ferromagnetic and semiconductor systems, and this system may be used as a voltage-tunable magnetoresistance device. [ABSTRACT FROM AUTHOR]

Bothriochloa ischaemum grasslands cover a large area of central China. A total of 81 grassland quadrats of 2 m × 2 m were established randomly in nine counties of central China. Data for species composition, abundance, coverage and height, plus several environmental variables were measured and recorded in each quadrat. Dry biomass and productivity for three associations within three counties were also determined. Species data of importance values were used in the two-way indicator species analysis (TWINSPAN) and the detrended correspondence analysis (DCA) ordination. A total of 11 main grassland associations were distinguished by the TWINSPAN classification; all of them being secondary vegetation. Each association had its own characteristics in composition, structure, productivity and environment. The results of DCA show that the distribution of B. ischaemum grasslands and associated species are closely related to longitude, that is, related to a moisture gradient. Precipitation was one of the most important factors affecting the distribution of the studied grasslands. In addition, topographic factors, such as elevation, aspect, slope and soil types, were also correlated to grassland vegetation. The distribution of grassland associations was consistent to that of their dominant species. TWINSPAN and DCA revealed the same ecological gradients in this study. These grasslands are important for regional development of animal husbandry and economy, although their productivity is not very high. Effective protocols for the conservation and management of B. ischaemum grasslands are needed. [ABSTRACT FROM AUTHOR]