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Sun H.-M.,National Tsing Hua University | Wang H.,National Tsing Hua University | Wang K.-H.,Hong Kong Institute of Technology | Chen C.-M.,National Tsing Hua University
IEEE Transactions on Computers | Year: 2011

As new vulnerabilities on Windows systems are reported endlessly, it is more practical to stop polymorphic malicious code from exploiting these vulnerabilities by building an behavior-based monitor, rather than adopting a signature-based detection system or fixing these vulnerabilities. Many behavior-based monitors have been proposed for Windows systems to serve this purpose. Some of them hook high-level system APIs to detect the suspicious behaviors of code. However, they cannot detect malicious code that directly invokes Native APIs. In this paper, we present a novel security scheme that hooks Native APIs in the kernel mode. This method effectively prevents malicious code calling Native APIs directly. It introduces an average eight percent computation overhead into the system. Analyses and a series of experiments are given in the paper to support our claims. © 2011 IEEE.

Zhou Y.,Hong Kong Institute of Technology
Solid State Communications | Year: 2010

I studied theoretically the enhancement of remanent polarization and dielectric permittivity of interfacial-coupled ferroelectric superlattices based on the LandauGinzburg theory. Our model adopts the LandauKhalatnikov equation to describe hysteresis behavior and takes the time-dependent space-charge-limited conductivity into account to investigate the ferroelectric and dielectric properties of ferroelectric superlattices. The results are in good agreement with recent experimental observations on the enhancement of remanent polarization and permittivity of BaTiO3SrTiO3 superlattices and heterolayered Pb(Zr,Ti)O3 thin films. © 2010 Elsevier Ltd. All rights reserved.

Zhou Y.,Hong Kong Institute of Technology
Nanotechnology | Year: 2011

A simple model is developed to investigate the potential profile changes due to mechanical stress at the ferromagnetic/ferroelectric interfaces of ferromagnetic-ferroelectric-ferromagnetic tunnel junctions with an ultrathin ferroelectric barrier. The potential changes associated with the polarization variation have significant effects on the tunneling conductance of the junctions. The discovered effect is illustrated by the example of a multiferroic tunnel junction in which approximately four orders of changes of the tunneling conductance and several-fold changes of the tunneling magnetoresistance (TMR) are observed due to the spin-flip induced nanomechanical stress. The TMR modulation effect is essential for realization of novel spintronics nano-devices as well as being useful for investigating fundamental aspects of the spin transfer. © 2011 IOP Publishing Ltd.

We have studied the effect of the fieldlike spin torque term bJ, present in magnetic tunneling junctions (MTJs) with perpendicular magnetic anisotropy in the free layer, on switching characteristics of the devices. We find that bJ has a strong impact on the switching current density and switching speed. The theoretical limit of the switching current density can be significantly reduced and the theoretical limit of the switching time will be lowered compare to the spin-valve (SV) devices. These results strongly suggest that the spin transfer torque random access memory based on the MTJs with perpendicularly magnetized free layer will likely have the multiple benefits of much larger intrinsic signal, smaller switching current, and faster switching speed than the SV devices. © 2011 American Institute of Physics.

Zhou Y.,Hong Kong Institute of Technology
Solar Energy | Year: 2012

In this work, we propose the compositionally graded ferroelectrics (CGF) as solar energy harvesting device. Such a novel geometrically frustrated system exhibits an intrinsic built-in potential which can be used to separate the hole and electron currents. It is shown that the CGF based photovoltaic devices can achieve orders of higher efficiency than bulk/non-graded ferroelectric thin films. The dependence of the photovoltaic effect on various device parameters have also been investigated. © 2011 Elsevier Ltd.

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