ANALYSIS OF THE PERFORMANCE OF NON-UNIFORMLY ACTIVE CATALYST PELLETS FOR A NON-ISOTHERMAL SERIES REACTION

An analysis of the influence of the non-uniform distribution of the active species in a catalyst pellet on the effectiveness factor and selectivity for the case of a series non-isothermal reaction is carried out. The case in which the desired reaction has a lower activation energy than the undesired reaction is considered. The effect of different reaction parameters on the selectivity for a single pellet is studied, and the optimum activity distribution is determined for high values of Thiele modulus. It is shown that temperature gradients within the pellet have a detrimental effect on local and overall selectivity and that these gradients are a strong function of the distribution of catalytically active material within the pellet.     

Species segregation of binary mixtures and a continuous size distribution of Group B particles in riser flow

Experiments involving a gas–solid, pilot-scale circulating fluidized bed (CFB) have been carried out, with a focus on species segregation measurements in a riser. Three mixtures were considered: (i) a binary mixture with particles of different sizes (d_ave) but same material density (ρ_s), (ii) a binary mixture with particles of different material densities (ρ_s) but same size (d_ave), and (iii) a continuous particle size distribution (PSD). Local measurements of the composition (i.e., species segregation) of each mixture were obtained over a range of operating conditions. Similar to previous works, the results show that the more massive species (i.e., greater d_ave or ρ_s) preferentially segregates toward the wall in all cases. Several new trends were also observed. First, for the binary mixtures, composition of the more massive species increases with riser height at the wall under some operating conditions. The operating conditions that cause this phenomenon are mutually exclusive for the size-difference and density-difference systems. Second, for the continuous PSD, radial segregation is observed even when there is a net positive flux in the annular region, contrary to previous findings which indicated segregation only for conditions leading to a net downward flux in the annular region. Finally, two qualitative differences between the binary and continuous mixtures were noted: (i) a monotonic decrease in species segregation is observed for the binary mixtures with an increase in the solid loading (m), while a non-monotonic trend is observed for the continuous PSD, and (ii) while the shape of the radial segregation profile is flattest at the riser bottom for the binary mixtures, the flattest radial profile is at the riser top for the continuous PSD.     

Regenerative energy control system for plug-in hydrogen fuel cell scooter

An intelligent control system was developed using simple control methodologies for an H₂-powered fuel cell scooter with the aid of a built-in microprocessor. This system increases the power input to drive a hydrogen fuel cell scooter, particularly during uphill conditions by running both the batteries and the fuel cell source in parallel. This system also improves the energy management of the scooter by recharging the battery using the fuel cell as well as automatic switching to the battery source when the hydrogen fuel cell is running low on hydrogen. This system was tested on a bench set simulating a 254 W hydrogen fuel cell stack equipped on a 200 W scooter. The test rig set-up depicts a practical scooter running on various load conditions. These results reflect the efficiencies of actual running conditions. The entire operation was embedded in a PICAXE-18 microcontroller for automatic switching between the batteries and the fuel cell source. An increase in the DC motor efficiency by 6 % has been shown. The uphill angle of the scooter has been increased by 19.3 %, which means the scooter would be able to travel on steeper hills. Copyright © 2007 John Wiley & Sons, Ltd.     

Collagenase-3 (matrix metalloproteinase-13) expression is induced in oral mucosal epithelium during chronic inflammation

Increased proliferation of mucosal epithelium during inflammation is associated with degradation of subepithelial connective tissue matrix and local invasion of the epithelial cells. Here we have studied, whether collagenase-3 (MMP-13), a collagenolytic matrix metalloproteinase with an exceptionally wide substrate specificity, is expressed in the epithelium of chronically inflamed mucosa. Examination of human gingival tissue sections from subjects with chronic adult periodontitis with in situ hybridization revealed marked expression of MMP-13 in basal cells of some epithelial rete ridges expanding into connective tissue. Immunohistochemical staining demonstrated that these cells also expressed strongly laminin-5, suggesting that they are actively migrating cells. A strong signal for MMP-13 mRNA was occasionally also noted in the suprabasal epithelial cells facing the gingival pocket, whereas no collagenase-1 (MMP-1) mRNA was detected in any areas of the epithelium. MMP-13 expression was also detected in fibroblast-like cells associated with collagen fibers of the inflamed subepithelial connective tissue. In organ culture of human oral mucosa, MMP-13 mRNA expression was observed in epithelial cells growing into connective tissue of the specimens. Regulation of MMP-13 expression was examined in cultured normal nonkeratinizing epithelial cells isolated from porcine periodontal ligament. In these cells, MMP-13 expression at the mRNA and protein level was potently enhanced (up to sixfold) by tumor necrosis factor-alpha, transforming growth factor-beta(1), and transforming growth factor-alpha and by keratinocyte growth factor in the presence of heparin. In addition, plating periodontal ligament epithelial cells on type I collagen stimulated MMP-13 expression (sevenfold) as compared with cells grown on tissue culture plastic. The results of this study show, that expression of MMP-13 is specifically induced in undifferentiated epithelial cells during chronic inflammation due to exposure to cytokines and collagen. Thus, it is likely that MMP-13 expression is instrumental in the subepithelial collagenolysis and local invasion of the activated mucosal epithelium into the connective tissue.     

Progress Towards an Optimization Methodology for Combustion-Driven Portable Thermoelectric Power Generation Systems

There is enormous military and commercial interest in developing quiet, lightweight, and compact thermoelectric (TE) power generation systems. This paper investigates design integration and analysis of an advanced TE power generation system implementing JP-8 fueled combustion and thermal recuperation. In the design and development of this portable TE power system using a JP-8 combustor as a high-temperature heat source, optimal process flows depend on efficient heat generation, transfer, and recovery within the system. The combustor performance and TE subsystem performance were coupled directly through combustor exhaust temperatures, fuel and air mass flow rates, heat exchanger performance, subsequent hot-side temperatures, and cold-side cooling techniques and temperatures. Systematic investigation and design optimization of this TE power system relied on accurate thermodynamic modeling of complex, high-temperature combustion processes concomitantly with detailed TE converter thermal/mechanical modeling. To this end, this paper reports integration of system-level process flow simulations using CHEMCAD? commercial software with in-house TE converter and module optimization, and heat exchanger analyses using COMSOL? software. High-performance, high-temperature TE materials and segmented TE element designs are incorporated in coupled design analyses to achieve predicted TE subsystem-level conversion efficiencies exceeding 10%. These TE advances are integrated with a high-performance microtechnology combustion reactor based on recent advances at Pacific Northwest National Laboratory (PNNL). Predictions from this coupled simulation approach lead directly to system efficiency?Cpower maps defining potentially available optimal system operating conditions and regimes. Further, it is shown that, for a given fuel flow rate, there exists a combination of recuperative effectiveness and hot-side heat exchanger effectiveness that provides a higher specific power output from the TE modules. This coupled simulation approach enables pathways for integrated use of high-performance combustor components, high-performance TE devices, and microtechnologies to produce a compact, lightweight, combustion-driven TE power system prototype that operates on common fuels.     

ANN virtual sensors for emissions prediction and control

This paper demonstrates the use of artificial neural networks virtual sensors in emissions prediction and control for a gasoline engine. Tailpipe emissions and engine parameters were first measured experimentally to form a comprehensive database for network training and testing. Individual predictive models were constructed using the optimization layer-by-layer neural network. Simulation results demonstrated that the networks, as virtual sensors, can accurately predict the engine parameters and emissions quantitatively and qualitatively with RMS errors below 9%. The second part of this paper then presents a virtual sensor control model which is the combination of the two individual emissions and engine predictive models developed previously. The main objective of this part is to control the exhaust emissions within the desired limits by predicting optimum engine parameters with the use of artificial neural network virtual sensors. Results showed that the emissions levels were successfully controlled within the defined limits, with maximum tolerance of 6%. This first part of this paper demonstrated that with the use of artificial neural network virtual sensors, emissions and engine parameters can be accurately predicted. Hence with accurate virtual sensors, emissions were then controlled within the desired limits by optimizing the engine parameters. This proposed work demonstrated a viable and accurate methodology in emissions predictive and control. By applying virtual sensor models, the need additional, cumbersome and costly measuring and monitoring devices can be eliminated.     

Interpretation of single-particle negative polarization at intermediate scattering angles

We study the interrelation of the internal field of irregular particles to the far-field scattering characteristics by modifying the internal field of dipole groups. In this paper, we concentrate on the longitudinal component, i.e., the internal-field component parallel to the incident wave vector. We use the discrete-dipole approximation to determine the internal field and switch off the longitudinal component from the dipoles that have the highest energy density above a preset cutoff value. We conclude that only a relatively small number of core dipoles, about 5% of all dipoles, contribute to the negative linear polarization at intermediate scattering angles. These core dipole groups are located at the forward part of the particles. The number of core dipoles in the group becomes greater as particle asphericity increases. We find that the interference between the scattered waves from the core dipole groups, which was studied previously for spherical particles, is preserved to a large extent for nonspherical particles.     

Algorithm level re-computing using implementation diversity: a register transfer level concurrent error detection technique

Concurrent error detection (CED) based on time redundancy entails performing the normal computation and the re-computation at different times and then comparing their results. Time redundancy implemented can only detect transient faults. We present two algorithm-level time-redundancy-based CED schemes that exploit register transfer level (RTL) implementation diversity to detect transient and permanent faults. At the RTL, implementation diversity can be achieved either by changing the operation-to-operator allocation or by shifting the operands before re-computation. By exploiting allocation diversity and data diversity, a stuck-at fault will affect the two results in two different ways. The proposed schemes yield good fault detection probability with very low area overhead. We used the Synopsys behavior complier (BC), to validate the schemes.     

Time-constrained scheduling during high-level synthesis offault-secure VLSI digital signal processors

Advances in VLSI technology are making it feasible to pack millions of transistors on a single chip. A consequent increase in the number of on-chip faults as well as the growing importance of quality-metrics such as reliability and fault-tolerance are making on-chip fault-tolerance mandatory. On-chip realization of a computation is fault-secure if an observable error in the computation is detected. Components used in life-critical systems should be secured against all faults. While fault-security can be realized by duplicating the computation on disjoint hardware and voting on the result(s), such straightforward strategies entail appreciable hardware overhead. This paper presents computer-aided behavioral synthesis of fault-secure microarchitectures which require less than proportional increase in hardware. The strategy selects intermediate computations for additional voting. The resulting class of fault-secure microarchitectures supplants the enormous hardware requirements of naive fault-secure strategies with enhanced hardware utilization afforded by securing the intermediate computations. Experimental results show that fault-security can be implemented at a less than proportional increase in hardware overhead