Measurement of Onset of Structural Relaxation in Melt-Quenched Phase Change Materials

Chalcogenide phase change materials enable non-volatile, low-latency storage-class memory. They are also being explored for new forms of computing such as neuromorphic and in-memory computing. A key challenge, however, is the temporal drift in the electrical resistance of the amorphous states that encode data. Drift, caused by the spontaneous structural relaxation of the newly recreated melt-quenched amorphous phase, has consistently been observed to have a logarithmic dependence in time. Here, it is shown that this observation is valid only in a certain observable timescale. Using threshold-switching voltage as the measured variable, based on temperature-dependent and short timescale electrical characterization, the onset of drift is experimentally measured. This additional feature of the structural relaxation dynamics serves as a new benchmark to appraise the different classical models to explain drift.     

Vibrational Energy Transport in Hybrid Ordered/Disordered Nanocomposites: Hybridization and Avoided Crossings of Localized and Delocalized Modes

Vibrational energy transport in disordered media is of fundamental importance to several fields spanning from sustainable energy to biomedicine to thermal management. This work investigates hybrid ordered/disordered nanocomposites that consist of crystalline membranes decorated by regularly patterned disordered regions formed by ion beam irradiation. The presence of the disordered regions results in reduced thermal conductivity, rendering these systems of interest for use as nanostructured thermoelectrics and thermal device components, yet their vibrational properties are not well understood. Here, the mechanism of vibrational transport and the reason underlying the observed reduction is established in detail. The hybrid systems are found to exhibit glass‐crystal duality in vibrational transport. Lattice dynamics reveals substantial hybridization between the localized and delocalized modes, which induces avoided crossings and harmonic broadening in the dispersion. Allen/Feldman theory shows that the hybridization and avoided crossings are the dominant drivers of the reduction. Anharmonic scattering is also enhanced in the patterned nanocomposites, further contributing to the reduction. The systems exhibit features reminiscent of both nanophononic materials and locally resonant nanophononic metamaterials, but operate in a manner distinct to both. These findings indicate that such “patterned disorder” can be a promising strategy to tailor vibrational transport through hybrid nanostructures.     

A multiparameter wearable physiologic monitoring system for space and terrestrial applications.

A novel, unobtrusive and wearable, multiparameter ambulatory physiologic monitoring system for space and terrestrial applications, termed LifeGuard, is presented. The core element is a wearable monitor, the crew physiologic observation device (CPOD), that provides the capability to continuously record two standard electrocardiogram leads, respiration rate via impedance plethysmography, heart rate, hemoglobin oxygen saturation, ambient or body temperature, three axes of acceleration, and blood pressure. These parameters can be digitally recorded with high fidelity over a 9-h period with precise time stamps and user-defined event markers. Data can be continuously streamed to a base station using a built-in Bluetooth RF link or stored in 32 MB of on-board flash memory and downloaded to a personal computer using a serial port. The device is powered by two AAA batteries. The design, laboratory, and field testing of the wearable monitors are described.     

No Shades of Gray: The Binary Discourse of George W. Bush and an Echoing Press

Binary communications represent the world as a place of polar opposites. Such conceptions of reality, although not uncommon in Western thought, take on a heightened importance when political leaders employ them in a concerted, strategic discourse in a mass media environment. With this in mind, this research offers a conception of binary discourse and uses this as a foundation to examine (a) the use of binaries by U.S. President George W. Bush in 15 national addresses, from his inauguration in January 2001 to commencement of the Iraq War in March 2003, and (b) the responses of editorials in 20 leading U.S. newspapers to the president's communications.     

Phase transformations in thermally exposed Au-Al ball bonds

Gold-aluminum ball bonds were thermally exposed at constant elevated temperatures, and the resultant phase transformations studied in detail. The as-bonded microstructure of a Au-Al ball bond essentially consisted of a reaction zone (termed “alloyed zone” (AZ) in the as-bonded condition) between the Au bump and the bonded Al metallization. It is the growth of the reaction zone between the Au bump and the bonded Al metallization and also the nonbonded Al metallization during thermal exposure that gave rise to the various phase transformations. Au₄Al, Au₈Al₃, and Au₂Al are the predominant phases that grew across the ball bond until the bonded Al metallization is available to take part in the interdiffusion reactions. After the complete consumption of the bonded Al metallization, the Au-Al phases reverse transformed resulting in the formation of the Au₄Al phase in the entire reaction zone across the ball bond (RZ-A). The lateral interdiffusion reactions resulted in the nucleation and the growth of all of the Au-Al phases given by the phase diagram. Kidson’s analysis and Tu et al.’s treatment were extended to a five-phase binary system to explain the phase transformations in thermally exposed Au-Al ball bonds. It is possible for all of the Au-Al phases to grow across a ball bond uninhibited as long as the bonded metallization is available. However, the supply limitation of the bonded metallization gives rise to reverse transformations where Al-rich phases transform to Au-rich phases and eventually result in the formation of the Au₄Al phase in the entire RZ-A. If infinite time is allowed, Au₄Al would dissolve; the extent of which is dependent on the solubility of Al in Au. No supply of Au lateral to the bond causes the reverse transformation of the Au₄Al phase, giving rise to the lateral growth of the remaining Au-Al phases. If infinite time is allowed, the lateral phase transformations would result in the formation of a phase that is dependant on the relative proportion of Au and Al present in the nonbonded metallization (NBM) and Au₄Al below the void line. Hence, the presence of a phase in a particular location of a ball bond is dependent on the time and temperature of thermal exposure.     

A Dual-Fed, Self-Diplexing PIFA and RF Front-End

A dual-fed, self-diplexing planar inverted F antenna and an associated RF front-end are described. It is shown that co-design of the antenna and front-end can be used to double the operational bandwidth, without significant size or performance penalties. Indeed, the use of two feeds allows the antenna to be self-diplexing, which results in improved overall efficiency     

X‐Region: A framework for location privacy preservation in mobile peer‐to‐peer networks

While enjoying various LBS (location‐based services), users also face the threats of location privacy disclosure. This is because even if the communications between users and LBS providers can be encrypted and anonymized, the sensitive information inside LBS queries may disclose the exact location or even the identity of a user. The existing research on location privacy preservation in mobile peer‐to‐peer (P2P) networks assumed that users trust each other and directly share location information with each other. Nonetheless, this assumption is not practical for most of the mobile P2P scenarios, for example, an adversary can pretend to be a normal user and collect the locations of other users. Aiming at this issue, this paper presents x‐region as a solution to preserve the location privacy in a mobile P2P environment where no trust relationships are assumed amongst mobile users. The main idea is to allow users to share a blurred region known as x‐region instead of their exact locations so that one cannot distinguish any user from others inside the region. We propose a theoretical metric for measuring the anonymity property of x‐region, together with three algorithms for generating an x‐region, namely, benchmark algorithm, weighted expanding algorithm, and aggressive weighted expanding algorithm. These algorithms achieve the anonymity and QoS requirements with different strategies. Our experiments verify the performance of the algorithms against three key metrics. Copyright © 2013 John Wiley & Sons, Ltd.     

Stochastic Screen Halftoning for Electronic Imaging Devices

For numerous digital imaging applications, there is a need to maintain the highest quality perceived image, while utilizing a printer or display that can only achieve a limited number of output states. Digital halftoning is the approach that has been widely used to meet this demand. In this focus paper, we provide a short summary of halftone techniques, then we concentrate on the newer and expanding roles of stochastic halftone screens—which are free of regular periodic structures and have numerous advantages in quality color rendering. We address some theoretical issues, design and optimality issues, printer compensation issues, and color quality issues that pertain to the development and use of stochastic screens for electronic imaging devices.     

Quasi‐One Dimensional in‐Plane Conductivity in Filamentary Films of PEDOT:PSS

The mechanism and magnitude of the in‐plane conductivity of poly(3,4‐ethy‐lenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) thin films is determined using temperature dependent conductivity measurements for various PEDOT:PSS weight ratios with and without a high boiling solvent (HBS). Without the HBS the in‐plane conductivity of PEDOT:PSS is lower and for all studied weight ratios well described by the relation $ \sigma = \sigma _0 {\rm exp}[- \left({{{{T_0}}\over{T}}} \right)^{0.5}] $ with T₀ a characteristic temperature. The exponent 0.5 indicates quasi‐one dimensional (quasi‐1D) variable range hopping (VRH). The conductivity prefactor σ₀ varies over three orders of magnitudes and follows a power law σ₀∝c^3.5_PEDOT with c_PEDOT the weight fraction of PEDOT in PEDOT:PSS. The field dependent conductivity is consistent with quasi‐1D VRH. Combined, these observations suggest that conductance takes place via a percolating network of quasi‐1D filaments. Using transmission electron microscopy (TEM) filamentary structures are observed in vitrified dispersions and dried films. For PEDOT:PSS films with HBS, the conductivity also exhibits quasi‐1D VRH behavior when the temperature is less than 200 K. The low characteristic temperature T₀ indicates that HBS‐treated films are close to the critical regime between a metal and an insulator. In this case, the conductivity prefactor scales linearly with c_PEDOT, indicating the conduction is no longer limited by a percolation of filaments. The lack of observable changes in TEM upon processing with the HBS suggests that the changes in conductivity are due to a smaller spread in the conductivities of individual filaments, or a higher probability for neighboring filaments to be connected rather than being caused by major morphological modification of the material.