17,993 research outputs found
Electron Band Structure in a Two Dimensional Periodic Magnetic Field
In this paper we study the energy spectrum of a two dimensional electron gas
(2DEG) in a two dimensional periodic magnetic field. Both a square magnetic
lattice and a triangular one are considered. We consider the general case where
the magnetic field in a cell can be of any shape. A general feature of the band
structure is bandwidth oscillation as a function of the Landau index. A
triangular magnetic lattice on a 2DEG can be realized by the vortex lattice of
a superconductor film coated on top of a heterojunction. Our calculation
indicates a way of relating the energy spectrum of the 2DEG to the vortex
structure. We have also derived conditions under which the effects of a weak
magnetic modulation, periodic or not, may be reproduced by an electric
potential modulation, and vice versa.Comment: 16 pages in TeX and 5 uuencoded figure
Adaptive just-in-time code diversification
We present a method to regenerate diversified code dynamically in a Java bytecode JIT compiler, and to update the diversification frequently during the execution of the program. This way, we can significantly reduce the time frame in which attackers can let a program leak useful address space information and subsequently use the leaked information in memory exploits. A proof of concept implementation is evaluated, showing that even though code is recompiled frequently, we can achieved smaller overheads than the previous state of the art, which generated diversity only once during the whole execution of a program
Relay Assisted Cooperative OSTBC Communication with SNR Imbalance and Channel Estimation Errors
In this paper, a two-hop relay assisted cooperative Orthogonal Space-Time
Block Codes (OSTBC) transmission scheme is considered for the downlink
communication of a cellular system, where the base station (BS) and the relay
station (RS) cooperate and transmit data to the user equipment (UE) in a
distributed fashion. We analyze the impact of the SNR imbalance between the
BS-UE and RS-UE links, as well as the imperfect channel estimation at the UE
receiver. The performance is analyzed in the presence of Rayleigh flat fading
and our results show that the SNR imbalance does not impact the spatial
diversity order. On the other hand, channel estimation errors have a larger
impact on the system performance. Simulation results are then provided to
confirm the analysis.Comment: 5 pages, 3 figures, IEEE 69th Vehicular Technology Conferenc
Co-movements of Shanghai and New York Stock prices by time-varying regressions
We estimate a time-varying regression model to study the relationship between returns in the Shanghai and New York stock markets, with possible inclusion of lagged returns. The parameters of the regressions reveal that the effect of the current stock return for New York on that for Shanghai steadily increases after the 1997 Asian financial crisis and turns significantly and persistently positive after 2002, when China entered WTO. The effect of the current return for Shanghai on New York also becomes significantly positive and increasing after 2002. The upward trend has been interrupted during the recent global financial crisis, but reaches the level of about 0.4 to 0.5 in 2010 for both markets. Our results show that China’s stock market has become more and more integrated into the world market in the past twenty years, with interruptions occurring during the recent global economic downturn.China; globalization; rate of return; stock markets; time-varying parameter regression
Resistance status of the carmine spider mite, Tetranychus cinnabarinus and the twospotted spider mite, Tetranychus urticae to selected acaricides on strawberries.
The carmine spider mite, Tetranychus cinnabarinus (Boisduval) and the twospotted spider mite, Tetranychus urticae Koch, are serious pests of strawberries and many other horticultural crops. Control of these pests has been heavily dependent upon chemical acaricides. Objectives of this study were to determine the resistance status of these two pest species to commonly used acaricides on strawberries in a year-round intensive horticultural production region. LC90 of abamectin for adult carmine spider mites was 4% whereas that for adult twospotted spider mites was 24% of the top label rate. LC90s of spiromesifen, etoxazole, hexythiazox and bifenazate were 0.5%, 0.5%, 1.4% and 83% of their respective highest label rates for carmine spider mite eggs, 0.7%, 2.7%, 12.1% and 347% of their respective highest label rates for the nymphs. LC90s of spiromesifen, etoxazole, hexythiazox and bifenazate were 4.6%, 11.1%, 310% and 62% of their respective highest label rates for twospotted spider mite eggs, 3%, 13%, 432,214% and 15% of their respective highest label rates for the nymphs. Our results suggest that T. cinnabarinus have developed resistance to bifenazate and that the T. urticae have developed resistance to hexythiazox. These results strongly emphasize the need to develop resistance management strategies in the region
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