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260 Reverse Engineering – Recent Advances and Applications 18 Will-be-set-by-IN-TECH Current [×10 −4 moles/sec] 45 40 35 30 25 20 15 10 5 0 Experimental data Rope-Walk model Square-channel model Cayley tree model Rest Moderate Heavy Maximum Fig. 9. Comparison between predicted values and the means of the measured oxygen uptake rates/currents at varying exercise levels. exercise levels. This is reduction is balanced, however, with a drastic increase in the number of activated gas exchangers (Hou et al., 2010). Figure 9 compares the predictions of these models to the measured currents for each exercise regime as reported by (Hou et al., 2010). Due to the discrete nature of the square-channel model, the length of a channel is restricted to be an integer multiple of its diameter (Grebenkov et al., 2005). So, setting a = 0.0139 cm requires that l = 0.0760 cm /0.0139 cm = 5.47; however, we rounded this value down to l = 5. Nevertheless, all models give reasonable agreement with the available data for the currents, with the Rope-Walk model giving closest agreement. This should be contrasted with the entirely different treelike models. We find the Cayley model to perform better than the square-channel model when equating their smallest length scales. 7. Industrial applications of lung-derived robustness In this reverse engineering study, a finished product, the human lung, was deconstructed into its elementary processes/structures using mathematical modeling as the main investigative tool. Using this process, we uncovered a mechanism, termed diffusional screening, responsible for robustness of the prototypical lung studied here that functions by adjusting the area of the active zones in response to any loss of surface permeability, without any feedback loops or addition of any extra “hardware.” Because aspects of some engineered processes evolve according to Eqns. 4 to 6, such as voltages, chemicals, or temperatures, they may also benefit from similar robustness derived, in part, from a treelike/fractal exchange surface. Here we briefly review just few examples. 7.1 Fuel cells Fuel cells transduce chemical energy from a fuel (e.g. hydrogen, methane) into electrical energy through catalysis with an oxidizing agent (e.g. oxygen). Unfortunately, current devices lack the efficiency necessary to support wide-spread implementation in areas such as the transportation sector. Recent work, however, shows such efficiency can be improved 10-20% for a single cell of a stack-based setup using lung-inspired designs (Kjielstrup et al., 2010).
Reverse-Engineering the Robustness of Mammalian Lungs Reverse-Engineering the Robustness of Mammalian Lungs 19 7.2 Heterogeneous catalysis An active area of research in chemical engineering concerns the study of the chemical yield, and other properties, resulting from a gas or liquid reactant in contact with a solid nanoporous catalyst. It is known, for example, that the pore-size distribution influences the catalytic efficiency, wherein the reaction proceeds according to first-order kinetics (Gheorghui & Coppens, 2004). In this context Eqns. 4 to 6 describe the steady-state reactant concentration, while the total current, Eqn. 7, gives the yield. Although the resulting robustness of the lung’s treelike “design” might protect against potential problems such as catalytic poisoning, it is not optimal in the sense of maximizing the reaction yield (Gheorghiu & Coppens, 2004). 7.3 Heat distribution systems A nontrivial problem in thermal conduction is to efficiently distribute a localized heat source throughout a dissipation volume, preventing temperature increases at the source. Recent results from optimization analysis demonstrate the most efficient configuration of such a heat-transport network is treelike (Bejan, 2006). In many circumstances, temperature gradients evolve according to equations of the type in Eqns. 4 to 6, when heat is allowed to leak through the materials and into the environment (Carslaw & Jaeger, 1986). Results shown in Figs. 6 through 8 therefore equally describe heat transport across treelike and fractal surfaces, and suggest that treelike heat-pipe networks may be more tolerant to variations in material and manufacturing quality. 8. Conclusions Although the partial pressure difference of oxygen in the gas-exchange regions of mammalian lungs increases only two-fold under the heaviest exercise conditions, the actual current increases approximately 20–fold, leaving another mechanism to supply the difference. Reverse engineering using mathematical modeling revealed that, depending on the exercise level, portions of the exchange surface of alveolar membranes remain “inactive” in any oxygen transport, so that a smaller effective area is responsible for supplying the oxygen current to the blood. With increasing exercise/breathing states, increasing surface areas are activated, drastically increasing the total oxygen uptake rate. This screening mechanism is termed “diffusional screening.” Transitions between no- and partial-screening regimes mark a region in which the exploration length matches any decrease in the active zones due to oxygen inaccessibility to the exchange surface, establishing a broad plateau in the total current indicative of robustness. That is, altered diffusivity or permeability produces no change to the total current across several orders of magnitude, without the addition of any extra “hardware.” Other engineered systems, such as fuel cells, heterogeneous catalytic reactors, and heat pipes are described by the same fundamental processes: diffusion through a service volume and “reaction” along its surface. Using this information, structural designs of these industrial systems might be reengineered to mitigate the effects of uncertainties in manufacturing processes or material properties. 9. References [1] Bejan, A., and Lorente, S. (2006). Constructal theory of generation of configuration in nature and engineering. J. Appl. Phys., Vol. 100, pp. 041301. 261
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REVERSE ENGINEERING - RECENT ADVANC
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Contents Preface IX Part 1 Software
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Preface Introduction In the recent
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Preface XI and con’s related to t
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Preface XIII the step-by-step appli
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Part 1 Software Reverse Engineering
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4 Reverse Engineering - Recent Adva
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108 Table 1. Number of smoothers an
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1. Introduction 60 Surface Reconstr
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Surface Reconstruction from Unorgan
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1. Introduction A Systematic Approa
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A Systematic Approach for Geometric
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Integrating Reverse Engineering and
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Page 225 and 226: Integrating Reverse Engineering and
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