Silver-Polymer Composite Stars: Synthesis and Applications

Colloidal "silver stars" were synthesized upon poly(lactic-co-glycolic) acid nanosphere templates via a facile two-step silver reduction method. Myriad dendrimer-like Ag star morphologies were synthesized by varying the amount of poly(vinyl alcohol) and trisodium citrate used during silver reduction. Scanning electron microscopy studies revealed that star-shaped silver-polymer composites possessing nanoscopic, fractal morphologies with diameters ranging from 500 nm to 7 μm were produced. These composites have broad applications from antibacterial agents to catalysis; two such applications were tested here. Surface-enhanced Raman spectroscopy (SERS) studies showed multiple hot spots of SERS activity within a single star. Electrochemical catalysis experiments demonstrated the feasibility of using the silver stars instead of platinum for the oxygen reduction reaction in alkaline fuel cells.     

Uncertainty quantification and model validation of fatigue crack growth prediction

This paper presents a methodology for uncertainty quantification and model validation in fatigue crack growth analysis. Several models – finite element model, crack growth model, surrogate model, etc. – are connected through a Bayes network that aids in model calibration, uncertainty quantification, and model validation. Three types of uncertainty are included in both uncertainty quantification and model validation: (1) natural variability in loading and material properties; (2) data uncertainty due to measurement errors, sparse data, and different inspection results (crack not detected, crack detected but size not measured, and crack detected with size measurement); and (3) modeling uncertainty and errors during crack growth analysis, numerical approximations, and finite element discretization. Global sensitivity analysis is used to quantify the contribution of each source of uncertainty to the overall prediction uncertainty and to identify the important parameters that need to be calibrated. Bayesian hypothesis testing is used for model validation and the Bayes factor metric is used to quantify the confidence in the model prediction. The proposed methodology is illustrated using a numerical example of surface cracking in a cylindrical component.     

Efficiency of hydrogen recovery from reformate with a polymer electrolyte hydrogen pump

The energy efficiency of hydrogen recovery from mixtures of CO₂, H₂O, and H₂ by a polymer electrolyte hydrogen pump (PEHP) has been evaluated. The PEHP pumps protons across the polymer electrolyte, producing >99.99% pure H₂ and a concentrated CO₂ stream. Single stage PEHP experiments recovered 65% of the hydrogen with an energy efficiency of 50%. The energy efficiency is limited by hydrogen mass transport across the porous gas diffusion electrode. The mass transport resistance for hydrogen increases as H₂ is depleted from the CO₂/H₂ mixture by the PEHP. Analysis shows that a multistage PEHP with fixed applied potential difference can recover >90% of the hydrogen with an energy efficiency of 75%, whereas a novel multistage PEHP design with a programmed voltage profile can achieve >90% energy efficiency with >98% hydrogen recovery. © 2010 American Institute of Chemical Engineers AIChE J, 2011     

Enhancing electron field emission properties of UNCD films through nitrogen incorporation at high substrate temperature

The electron field emission (EFE) and electrochemical (EC) properties of N₂(10%)-incorporated ultra-nanocrystalline diamond (N₂-UNCD) films were investigated. Microstructure examination using TEM indicates that incorporating the N₂ species without the substrate heating induced the presence of stacking faults, which can be effectively suppressed by growing the films at elevated temperature. While the synthesis of N₂-UNCD without substrate heating can efficiently enhance the EC properties (large potential window with smaller background current) of the films, the EFE behavior of the films can be improved only when the films were grown at an elevated temperature. Moreover, coating the conducting N₂-UNCD on Si-tips can further enhance the EFE and CV behaviors, viz. (E₀)_tip = 5.0 V/μm with (J_e)_tip = 0.28 mA/cm² at 15 V/μm applied field and ΔE_p = 0.5 V with redox peak 170 μA were achieved.     

EVE: A Flexible SIMD Coprocessor for Embedded Vision Applications

In this paper we introduce EVE (embedded vision/vector engine), with a FlexSIMD (flexible SIMD) architecture highly optimized for embedded vision. We show how EVE can be used to meet the growing requirements of embedded vision applications in a power- and area-efficient manner. EVE’s SIMD features allow it to accelerate low-level vision functions (such as image filtering, color-space conversion, pyramids, and gradients). With added flexibility of data accesses, EVE can also be used to accelerate many mid-level vision tasks (such as connected components, integral image, histogram, and Hough transform). Our experiments with a silicon implementation of EVE show that it performs many low- and mid-level vision functions with a 3–12x speed advantage over a C64x+DSP, while consuming less power and area. EVE also achieves code size savings of 4–6x over a C64x+DSP for regular loops. Thanks to its flexibility and programmability, we were able to implement two end-to-end vision applications on EVE and achieve more than a 5× application-level speedup over a C64x+. Having EVE as a coprocessor next to a DSP or a general purpose processor, algorithm developers have an option to accelerate the low- and mid-level vision functions on EVE. This gives them more room to innovate and use the DSP for new, more complex, high-level vision algorithms.     

Relationship between lung inflammation, changes in lung function and severity of exposure in victims of the Bhopal tragedy

The world's worst chemical industrial disaster, which occurred at Bhopal on 2-3 December, 1984, resulted in considerable respiratory morbidity in the exposed population. Therefore, a study was planned to evaluate the relationship between lower respiratory tract inflammation, lung function and severity of exposure. Sixty patients exposed to methyl isocyanate and presenting with respiratory symptoms were studied using bronchoalveolar lavage (BAL) 1-7 yrs after the accident. Pulmonary function tests included forced vital capacity (FVC) and forced expiratory volume in one second (FEV1). An index of severity of exposure was derived retrospectively on the basis of the acute symptoms in the victims themselves or the occurrence of death among their family members. Total lung inflammatory cells (p < 0.01) and absolute numbers of macrophages (p = 0.01) and lymphocytes (p < 0.05) increased as severity of exposure increased. FEV1/FVC % (p = 0.05) was also significantly lower as severity of exposure increased. Moderately exposed subjects had significantly lower FEV1/FVC % (p < 0.05) compared to those mildly exposed. In nonsmokers, BAL neutrophils, both percentage and absolute numbers, showed significant negative correlations with FEV1 % predicted (rs = -0.350, p < 0.05; and rs = -0.374, p < 0.01, respectively). Neutrophil percentage was negatively correlated with FEV1/FVC % (rs = -0.378; p < 0.01). Absolute lymphocytes had significant negative correlations with FVC % pred (rs = -0.318; p < 0.05). Macrophages had significant positive correlations with FVC % pred (rs = 0.322; p < 0.05) and FEV1 % pred (rs = 0.433; p < 0.01). Radiographic abnormalities (International Labour Organization (ILO) classification) were associated with decline in FEV1 % pred (p < 0.05). This study suggests that pulmonary function abnormalities occur in gas-exposed subjects as a consequence of an abnormal accumulation of lung inflammatory cells (lymphocytes and neutrophils), and that the intensity of lung inflammation and reduction in pulmonary function are greater in severely exposed subjects. As it has been observed that decline in pulmonary function is associated with radiographic abnormalities, there is a suggestion that injury following toxic gas exposure can lead to irreversible lung damage.     

Computer communication as an aid to independence for older adults

Computer and communication technologies offer the potential of improving die quality of life for older people by providing them with links to information and services outside of the home. This study examined die feasibility of older people using an electronic text message system to perform routine communication tasks. In addition information was gathered to identify design parameters which facilitate the interactions of older people with such computer based systems. A specialized and simplified 'communication computer' was placed in the homes of 36 older women, aged 50-95 years. The system was provided with: a simple text-editor, basic electronic mail functions and access to news/ weather, movie reviews, and health information. Both performance data and user preference data were collected. Results indicated that the participants liked using the system, were able to use it with minimal difficulty, and that it provided a valuable means for social interaction and mental stimulation. The findings suggest that computer-based systems can be a valuable support tool for older adults if they are easy to use, and provide applications that are useful for them.     

Microprocessor Determination of Phase Angle in the Presence of Harmonics

An instrument based on the look-up table technique in a microprocessor is developed to measure the phase angle between the fundamental components of two nonsinusoidal periodic signals. In real-time mode, the phase angle is measured with a resolution of 1°, while a resolution of 0.10° is achieved in the steady-state mode. Additional hardware is also incorporated to ensure that frequency variation in the range 45-55 Hz does not introduce any additional error in measurement.     

The use of multiuser detectors for multicasting in wireless ad hocCDMA networks

In this paper, we address the issue of performance of linear multiuser detectors for a multicasting application in an ad hoc wireless network. Using a code-division multiple-access (CDMA) framework, we demonstrate how capacity results for multiuser detectors can be adapted to do session admission control for the multicasting problem. We then develop a multicast routing algorithm for ad hoc wireless networks. Using the session admission control mechanism and the multicast routing algorithm, we evaluate the performance of three different linear multiuser detectors for the multicasting application     

A flux‐limited numerical method for solving the MHD equations to simulate propulsive plasma flows

For numerical simulations to be effective tools in plasma propulsion research, a high‐order accurate solver that captures MHD shocks monotonically and works reliably for strong magnetic fields is needed. For this purpose, a characteristics‐based scheme for the MHD equations, with flux limiters to improve spatial accuracy, has been developed. In this method, the symmetric form of the MHD equations, accounting for waves propagating in all directions, are solved. The required eigensystem of axisymmetric MHD equations, with appropriate normalization, is presented. This scheme was validated with unsteady (Riemann problem) and force‐free equilibrium (Taylor state) test cases, as well as with measured current density patterns in a magnetoplasmadynamic thruster. Copyright © 2001 John Wiley & Sons, Ltd.