Nitrogen-modified carbon-based catalysts for oxygen reduction reaction in polymer electrolyte membrane fuel cells

Nitrogen-modified carbon-based catalysts for oxygen reduction were synthesized by modifying carbon black with nitrogen-containing organic precursors. The electrocatalytic properties of catalysts were studied as a function of surface pre-treatments, nitrogen and oxygen concentrations, and heat-treatment temperatures. On the optimum catalyst, the onset potential for oxygen reduction is approximately 0.76 V (NHE) and the amount of hydrogen peroxide produced at 0.5 V (NHE) is approximately 3% under our experimental conditions. The characterization studies indicated that pyridinic and graphitic (quaternary) nitrogens may act as active sites of catalysts for oxygen reduction reaction. In particular, pyridinic nitrogen, which possesses one lone pair of electrons in addition to the one electron donated to the conjugated π bond, facilitates the reductive oxygen adsorption.     

Investigations on nucleation thermodynamical parameters of NdBa2Cu3O7-δ (Nd123) crystallization by high temperature solution growth

Investigations on nucleation thermodynamical parameters are very essential for the successful growth of good quality single crystals from high temperature solution. A theoretical estimation of the nucleation thermodynamical parameters like interfacial energy between the solid Nd123 and its flux BaO-CuO, metastable zone-width, Gibbs free energy, critical energy barrier for nucleation and critical nucleation radius have been calculated from the knowledge of solubility data and by applying the classical nucleation theory. Results are discussed to understand the growth kinetics of Nd123 crystals. Paper presented at the 5th IUMRS ICA98, October 1998, Bangalore     

Stress oscillations in plane stress modelling of flexure—a field-consistency interpretation

Exactly integrated isoparametric plane stress elements behave poorly in flexure. The 4-noded element ‘locks’, with errors that progress indefinitely as element aspect ratio increases. Reduced integration of the shear strain energy eliminates this locking entirely. The 8-noded element does not lock, but improves in performance with reduced integration of shear strain energy. Both elements, with their original shape functions, show severe shear stress oscillations in flexure. In this paper we attribute these oscillations to the lack of ‘consistency’ of shear strain fields derived directly from independent field-variable interpolations. We derive error models for specific tractable examples which can confirm the accuracy of this conceptual scheme through digital computation using the finite element models. A field-consistent redistribution strategy for the shear strain field is offered as an elegant procedure to free the elements of spurious oscillations and give a ‘lock’-free performance.     

Leveraging resources in global software development

Leveraging global resources for software development is rapidly becoming the norm at Motorola, which has over 25 software development centers worldwide. Our project, called the 3G Trial (Third Generation Cellular System), was the first of its scope and significance developed by a global engineering team at Motorola. Staffing was the most significant issue we encountered in the 3G Trial. We had only about 20 percent of the required staff available at our division headquarters in Burlington Heights, Ill., US, and needed to find the other 80 percent to successfully complete the project. Early on, we concluded that our only means to staff the project was to rely on software development engineers from Motorola's worldwide software centers. We developed the system with staffing from six different countries. Next, we had to integrate the people into a team. While addressing this challenge, we identified key risk factors and developed approaches to reduce them. We separated the project risk factors into the five categories Carmel (1999) describes as the centrifugal forces that pull global projects apart. To pass on the lessons we learned from this project, this article sets out the global development issues we faced, our approaches to resolving them, and our findings compared to other research     

Joint trellis-coded quantisation/modulation

Joint trellis-coded quantisation (TCQ) and trellis-coded modulation (TCM) can achieve considerable signal-to-quantisation noise ratios with moderate complexity. TCM is replaced with turbo TCM (TTCM) and simulation results given which show that the new scheme can achieve the same performance as that possible using by trellis-coded scalar quantisation at an SNR slightly above the channel capacity bound     

Yellow Beads and Missing Particles: Trouble Ahead for Filter-Based Absorption Measurements

Particulate emissions from low-temperature biomass burning are dominated by organic matter. Here, we show that such emissions have a liquid, bead-like appearance when collected on fibrous filters, and the number of these beads are far less than expected for solid spherical particles. These shapes are in line with published drop-on-fiber theories for liquids entrained on filaments. A smoldering pine sample is yellowish, with organic carbon over 99% of the total carbon, and chars substantially in thermal-optical analysis (TOA), indicating that such liquid organic particles could affect both absorption measurements and TOA of such samples. Similar colored samples collected in the field from rice-straw burning and cook stove emissions also show a similar liquid appearance.     

Local and Regional Secondary Organic Aerosol: Insights from a Year of Semi-Continuous Carbon Measurements at Pittsburgh

We present Scanning Mobility CCN Analysis (SMCA) as a novel method for obtaining rapid measurements of size-resolved cloud condensation nuclei (CCN) distributions and activation kinetics. SMCA involves sampling the monodisperse outlet stream of a Differential Mobility Analyzer (DMA) operated in scanning voltage mode concurrently with CCN and condensation particle counters. By applying the same inversion algorithm as used for obtaining size distributions with a scanning mobility particle sizer (SMPS), CCN concentration and activated droplet size are obtained as a function of mobility size over the timescale of an SMPS scan (typically 60–120 s). Methods to account for multiple charging, particle non-sphericity, and limited counting statistics are presented. SMCA is demonstrated using commercial SMPS and CFSTGC instruments with the manufacturer-provided control software. The method is evaluated for activation of both laboratory aerosol and ambient aerosol obtained during the 2004 NEAQS-ITCT2k4 field campaign. It is shown that SMCA reproduces the results obtained with a DMA operating in voltage “stepping” mode.     

Annealing studies of γ-titanium aluminides alloyed with light elements for creep strengthening

A fully-lamellar γ-titanium aluminide alloy containing carbon and silicon additions has been found to have superior creep resistance. The aging characteristics of this alloy, which also contains Nb, Cr, and W, have been studied by means of transmission electron microscopy techniques and are correlated to the post-crept microstructures. Precipitation of carbides and silicides along γ/γ interlamellar boundaries was observed during aging and creep deformation. The driving force for the precipitation reaction is the accommodation of excess amounts of carbon and silicon which have limited solubility in the γ-matrix. For comparison, the aging behavior of a Ti-46.8Al (at%) alloy containing carbon and boron has been assessed. It is found that the lamellar grain size is significantly smaller than the alloy without boron, but that equiaxed γ-grains also form during aging. In this alloy, carbides are observed to precipitate homogeneously within γ-laths and equiaxed grains.