In this paper, we present a new method of digital steganography, entitled spread spectrum image steganography (SSIS). Steganography, which means "covered writing" in Greek, is the science of communicating in a hidden manner. Following a discussion of steganographic communication theory and review of existing techniques, the new method, SSIS, is introduced. This system hides and recovers a message of substantial length within digital imagery while maintaining the original image size and dynamic range. The hidden message can be recovered using appropriate keys without any knowledge of the original image. Image restoration, error-control coding, and techniques similar to spread spectrum are described, and the performance of the system is illustrated. A message embedded by this method can be in the form of text, imagery, or any other digital signal. Applications for such a data-hiding scheme include in-band captioning, covert communication, image tamperproofing, authentication, embedded control, and revision tracking.
Phase change memory devices are based on the rapid and reversible amorphous-to-crystalline transformations of phase change materials, such as Ge2Sb2Te5 and AgInSbTe. Since the maximum switching speed of these devices is typically limited by crystallization speed, understanding the crystallization process is of crucial importance. While Ge2Sb2Te5 and AgInSbTe show very different crystallization mechanisms from their melt-quenched states, the nanostructural origin of this difference has not been clearly demonstrated. Here, we show that an amorphous state includes different sizes and number of nanoscale nuclei, after thermal treatment such as melt-quenching or furnace annealing is performed. We employ fluctuation transmission electron microscopy to detect nanoscale nuclei embedded in amorphous materials, and use a pump-probe laser technique and atomic force microscopy to study the kinetics of nucleation and growth. We confirm that melt-quenched amorphous Ge2Sb2Te5 includes considerably larger and more quenched-in nuclei than its as-deposited state, while melt-quenched AgInSbTe does not, and explain this contrast by the different ratio between quenching time and nucleation time in these materials. In addition to providing insights to the crystallization process in these technologically important devices, this study presents experimental illustrations of temperature-dependence of nucleation rate and growth speed, which was predicted by theory of phase transformation but rarely demonstrated.
This report presents a new method of digital steganography, entitled Spread-Spectrum Image Steganography (SSIS). Steganography, which means "covered writing" in Greek, is the science of communicating in a hidden manner. Following a brief history of this art and a discussion of steganographic communication theory, the new method, SSIS, is introduced. This system hides and recovers messages of substantial length within digital imagery while maintaining the original image size and dynamic range. The hidden messages can be recovered using appropriate keys without any knowledge of the original image. Image processing, error control coding, and spread-spectrum techniques utilized are described, and the performance of the technique is illustrated. A message embedded by this method can be in the form of text, imagery, or any other digital signal. Applications for such data-hiding scheme include in-band captioning, covert communication, image tamperproofing, authentication, embedded control, and revision tracking.
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