A highly efficient fire‐retardant nanomaterial based on carbon nanotubes and magnesium hydroxide

Hybrid buckypapers (HBP) were developed and showed potential as efficient fire‐retardant materials by implementing multiple fire retardance mechanisms. The fabrication of HBP was performed using multi‐walled carbon nanotubes (MWCNTs) and magnesium hydroxide (Mg(OH)₂) nanoparticles. The Mg(OH)₂ nanoparticles were well dispersed throughout the CNTs network, as revealed by scanning electron microscopy and Energy Dispersive X‐ray spectroscopy. Thermogravimetric analysis and differential scanning calorimetry both confirmed the decomposition of magnesium hydroxide in the HBPs and heat absorption under elevated temperatures. Our initial results indicated that when used as a skin layer, the HBP has the potential to significantly improve the fire‐retardant properties of epoxy carbon fiber composites. Copyright © 2012 John Wiley & Sons, Ltd.     

Coding static natural images using spiking event times: do neurons Cooperate?

To understand possible strategies of temporal spike coding in the central nervous system, we study functional neuromimetic models of visual processing for static images. We will first present the retinal model which was introduced by Van Rullen and Thorpe and which represents the multiscale contrast values of the image using an orthonormal wavelet transform. These analog values activate a set of spiking neurons which each fire once to produce an asynchronous wave of spikes. According to this model, the image may be progressively reconstructed from this spike wave thanks to regularities in the statistics of the coefficients determined with natural images. Here, we study mathematically how the quality of information transmission carried by this temporal representation varies over time. In particular, we study how these regularities can be used to optimize information transmission by using a form of temporal cooperation of neurons to code analog values. The original model used wavelet transforms that are close to orthogonal. However, the selectivity of realistic neurons overlap, and we propose an extension of the previous model by adding a spatial cooperation between filters. This model extends the previous scheme for arbitrary-and possibly nonorthogonal-representations of features in the images. In particular, we compared the performance of increasingly over-complete representations in the retina. Results show that this algorithm provides an efficient spike coding strategy for low-level visual processing which may adapt to the complexity of the visual input.     

Two types of natural graphite host matrix for composite activated carbon adsorbents

Two types of host for activated carbon (AC) adsorbents intended for use in compressed systems are studied: expanded natural graphite (ENG) and expanded natural graphite treated with acid (ENG-TA). Results show that compressed ENG-TA has much higher thermal conductivity than the compressed ENG. For a density of 830 kg/m³ the thermal conductivity of compressed ENG-TA is 336 W/(mK), and it is of the order of one hundred times higher compared with compressed ENG having similar density. The permeability of compressed ENG-TA is much more critical than the compressed ENG. For example for similar density of 300 kg/m³, the permeability of compressed ENG-TA is 2.01 × 10^?15 m² while the permeability of compressed ENG is 1.07 × 10^?13 m². Compressed composite adsorbents of AC with ENG as host were produced with a high density in the range 700–720 kg/m³. Considering that the permeability will be too low using composite AC with ENG-TA as host in high density, the density range was restricted to less than 500 kg/m³. The thermal conductivity of AC/ENG-TA composite is much higher than the thermal conductivity of AC/ENG composite, and it is about 7 times higher than the optimal value of AC/ENG composite.     

Outdoor rating conditions for photovoltaic modules and systems

Historically, flat-plate photovoltaic modules have been given a “peak-watt” rating indicating the power generated under 1000 W/m² global irradiance at a standard temperature. However, questions have arisen regarding the direct-normal irradiance, ambient or cell temperature, and wind speed (when it is specified) that should be used for evaluating the performance of flat-plate and concentrator modules. By studying the conditions that are observed when the global irradiance on a 2-axis-tracked surface is 1000 W/m², our analysis provides an objective, quantitative basis for the choice of the “peak-watt” rating conditions for both types of collectors. These observed conditions are consistent with commonly used values of 850 W/m² for direct-normal irradiance and 20°C for ambient temperature. Evidence is given that wind speed should be increased from the commonly used 1 m/s to a more frequently observed 4 m/s.     

Enhanced Chemiluminescence as an Indicator of Water Quality

The enhanced chemiluminescence test is based upon monitoring the emission of light from an enhanced chemiluminescence reaction in the presence of an environmental sample and comparing it with a similar reaction using a de-ionized water control sample. The presence of polluting materials can be detected by changes in the intensity and the kinetics of light emission. This trial demonstrated that the effects of components within a sewage-works' effluent are detected by enhanced chemiluminescence and that this test has moderately close correlation with parallel bacterial determinations. A high correlation was achieved between the performances of two commercially available enhanced chemiluminescence reagents, and these reagents responded consistently to the effects of a sewage-works' effluent on the quality of a small river.     

Flow modeling and simulation for vacuum assisted resin transfer molding process with the equivalent permeability method

Vacuum assisted resin transfer molding (VARTM) offers numerous advantages over traditional resin transfer molding, such as lower tooling costs, shorter mold filling time and better scalability for large structures. In the VARTM process, complete filling of the mold with adequate wet-out of the fibrous preform has a critical impact on the process efficiency and product quality. Simulation is a powerful tool for understanding the resin flow in the VARTM process. However, conventional three-dimensional Control Volume/Finite Element Method (CV/FEM) based simulation models often require extensive computations, and their application to process modeling of large part fabrication is limited. This paper introduces a new approach to model the flow in the VARTM process based on the concept of equivalent permeability to significantly reduce computation time for VARTM flow simulation of large parts. The equivalent permeability model of high permeable medium (HPM) proposed in the study can significantly increase convergence efficiency of simulation by properly adjusting the aspect ratio of HPM elements. The equivalent permeability model of flow channel can simplify the computational model of the CV/FEM simulation for VARTM processes. This new modeling technique was validated by the results from conventional 3D computational methods and experiments. The model was further validated with a case study of an automobile hood component fabrication. The flow simulation results of the equivalent permeability models were in agreement with those from experiments. The results indicate that the computational time required by this new approach was greatly reduced compared to that by the conventional 3D CV/FEM simulation model, while maintaining the accuracy, of filling time and flow pattern. This approach makes the flow simulation of large VARTM parts with 3D CV/FEM method computationally feasible and may help broaden the application base of the process simulation. Polym. Compos. 25:146–164, 2004. © 2004 Society of Plastics Engineers.