Electrical and Optical Properties of Conducting Polymer/Porous Silicon Structures

Electrical and optical properties of diode structures based on porous silicon (PS) and thin films of phenylene vinylene oligomer (PVO) have been studied. Steady-state photoluminescence spectroscopy show that the structure of the luminescence band depends on the PS morphology. We assign the observed effect to the morphology-dependent penetration of PVO material into the pores. Current-voltage characteristics of the PVO/PS diodes are studied and interpreted assuming Schottky emission and hopping transport of carriers aspossible mechanisms of d.c. electrical conduction.     

Molecular structure and rheological character of high-amylose water caltrop (Trapa bispinosa Roxb.) starch

The molecular structure and rheological properties of high-amylose water caltrop (Trapa bispinosa Roxb.) starch cultivated in Vietnam were investigated. The water caltrop starch had 47.1% amylose and its molecular weight (Mw) was (4.77±0.27)×10⁶ g/mol, whereas the Mw was (2.07±0.10)×10⁷ g/mol for amylopectin. The average chain length of amylopectin was DP_n=19.0 and the proportions of A, B₁, B₂, and B₃ chains were 28.2, 50.3, 13.1, and 8.5%, respectively. The DSC thermogram of the water caltrop starch was broadly endothermic, with 2 distinct endothermic peaks at 73.6 and 80.7°C. Gel formation of water caltrop starch occurred rapidly, with an extremely high storage modulus up to approximately 1,200 Pa. High-amylose water caltrop starch paste had an extremely high final viscosity compared to that of other cereal starches. These rheological behaviors may have been due to the extremely high amylose content.     

Development of a Risk-Ranking Framework to Evaluate Potential High-Threat Microorganisms, Toxins, and Chemicals in Food

ABSTRACT:  Through a cooperative agreement with the U.S. Food and Drug Administration, the Institute of Food Technologists developed a risk-ranking framework prototype to enable comparison of microbiological and chemical hazards in foods and to assist policy makers, risk managers, risk analysts, and others in determining the relative public health impact of specific hazard–food combinations. The prototype is a bottom-up system based on assumptions that incorporate expert opinion/insight with a number of exposure and hazard-related risk criteria variables, which are propagated forward with food intake data to produce risk-ranking determinations. The prototype produces a semi-quantitative comparative assessment of food safety hazards and the impacts of hazard control measures. For a specific hazard–food combination the prototype can produce a single metric: a final risk value expressed as annual pseudo-disability adjusted life years (pDALY). The pDALY is a harmonization of the very different dose–response relationships observed for chemicals and microbes. The prototype was developed on 2 platforms, a web-based user interface and an Analytica® model (Lumina Decision Systems, Los Gatos, Calif., U.S.A.). Comprising visual basic language, the web-based platform facilitates data input and allows use concurrently from multiple locations. The Analytica model facilitates visualization of the logic flow, interrelationship of input and output variables, and calculations/algorithms comprising the prototype. A variety of sortable risk-ranking reports and summary information can be generated for hazard–food pairs, showing hazard and dose–response assumptions and data, per capita consumption by population group, and annual p-DALY.     

Polyacrylonitrile‐carbon Nanotube‐polyacrylonitrile: A Versatile Robust Platform for Flexible Multifunctional Electronic Devices in Medical Applications

Flexible multifunctional electronic devices are of high interest for a wide range of applications including thermal therapy and respiratory devices in medical treatment, safety equipment, and structural health monitoring systems. This paper reports a scalable and efficient strategy of manufacturing a polyacrylonitrile‐carbon nanotube‐polyacrylonitrile (PAN‐CNT‐PAN) robust flexible platform for multifunctional electronic devices including flexible heaters, temperature sensors, and flexible thermal flow sensors. The key advantages of this platform include low cost, porosity, mechanical robustness, and electrical stability under mechanical bending, enabling the development of fast‐response flexible heaters with a response time of ≈1.5 s and relaxation time of ≈1.7 s. The temperature‐sensing functionality is also investigated with a range of temperature coefficient of resistances from ?650 to ?900 ppm K^?1. A flexible hot‐film sensing concept is successfully demonstrated using PAN‐CNT‐PAN with a high sensitivity of 340 mV (m s^?1)^?1. The sensitivity enhancement of 50% W^?1 is also observed with increasing supply power. The low cost, porosity, versatile, and robust properties of the proposed platform will enable the development of multifunctional electronic devices for numerous applications such as flexible thermal management, temperature stabilization in industrial processing, temperature sensing, and flexible/wearable devices for human healthcare applications.     

Model simplification and optimization of a passive wind turbine generator

In this paper, the design of a “low cost full passive structure” of wind turbine system without active electronic part (power and control) is investigated. The efficiency of such device can be obtained only if the design parameters are mutually adapted through an optimization design approach. For this purpose, sizing and simulating models are developed to characterize the behavior and the efficiency of the wind turbine system. A model simplification approach is presented, allowing the reduction of computational times and the investigation of multiple Pareto-optimal solutions with a multiobjective genetic algorithm. Results show that the optimized wind turbine configurations are capable of matching very closely the behavior of active wind turbine systems which operate at optimal wind powers by using a MPPT control device.     

Enhancement in High-Field J c Properties and the Flux Pinning Mechanism of MgB2 Thin Films on Crystalline SiC Buffer Layers

We have studied the influence of crystalline SiC buffer layers on the critical current density and on the flux pinning mechanism in MgB₂ thin films. Crystalline SiC buffer layers were deposited on the Al₂O₃ (0001) substrates by using a pulsed laser deposition method, and then MgB₂ thin films were grown on the SiC-buffered layer by using a hybrid physical-chemical vapor deposition technique. MgB₂ thin films with crystalline SiC-buffered layers showed a significant critical current density’s enhancement in the high magnetic field region. An uncommon plateau-like behavior was also observed when the normalized flux pinning force density was scaled with the reduced magnetic field. Based on the analyses of the scaling behavior of the flux pinning force, grain boundary pinning is likely to be a dominant pinning mechanism in the SiC-buffered MgB₂ thin films.     

Effect of trace Na additions on the hydriding kinetics of hypo-eutectic Mg–Ni alloys

Mg–Ni alloys are among the most promising candidates for solid-state hydrogen storage systems. This paper reveals the effect of Na doping in accelerating initial hydrogen uptake in Mg–Ni alloys using in-situ Synchrotron X-ray powder diffraction. A minimum concentration of approximately 0.2 wt.% Na must be achieved for the alloys to show reasonably fast hydriding kinetics. Surface analysis shows that a Na-modified Mg–Ni surface facilitates the chemisorption and dissociation of hydrogen molecules in the early stage of hydriding as evidenced by a rapid formation of the saturated hydrogen solid solution Mg₂NiH_0.3 from the original Mg₂Ni. The subsequent hydrogen absorption is based on a mechanism of nucleation and growth of MgH₂ where a high density of dislocations develops ahead of the growing hydride-metal interface.