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ABSTRACT: The determination of reaction pathways is one of the most important functions that should be performed in exploring the kinetics of catalyzed chemical reactions or biochemical reactions, the latter being generally catalyzed by enzymes. It is proven that the terms, "type-I extreme pathway" and "structurally minimal pathway", both introduced to characterize the kinetics of a catalyzed reaction are equivalent. These two terms are based on two distinct methodologies, one mainly rooted in convex analysis and the other in graph theory. The equivalence promises further even more effective methods for reaction-pathway identification by synergistic integration of existing ones.
Bioprocess and Biosystems Engineering 11/2012; · 1.81 Impact Factor
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ABSTRACT: A method and software are proposed for optimal assignment of vehicles to transportation tasks in terms of total cost and emission.
The assignment problem is transformed into a process-network synthesis problem that can be algorithmically handled by the
P-graph framework. In the proposed method, each task is given by a set of attributes to be taken account in the assignment;
this is also the case for each vehicle. The overall mileage is calculated as the sum of the lengths of all the routes to be
travelled during, before, after, and between the tasks (Desaulniers et al. 1998; Baita et al. 2000). Cost and emission are assigned to the mileages of each vehicle type. In addition to the globally optimal solution of the
assignment problem, the P-graph framework provides the n-best suboptimal solutions that can be ranked according to multiple criteria. The viability of the proposed method is illustrated
by an example.
KeywordsP-graph–Combinatorial optimization–Vehicle assignment–Transportation
Clean Technologies and Environmental Policy 04/2012; 13(4):637-642. · 1.75 Impact Factor
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Computers & Chemical Engineering. 01/2010; 34:700-706.
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Computers & Chemical Engineering. 01/2010; 34:821-824.
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Computers & Chemical Engineering. 01/2009; 33:1182-1186.
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Computers & Chemical Engineering. 01/2009; 33:687-698.
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ABSTRACT: A hierarchical approach is proposed to estimate the sustainability-potential of a chemical process, based on any of the alternative synthetic routes. This novel notion of sustainability-potential is a generalization of the notion of profit-potential, the estimation of which renders it possible to screen out economically nonviable processes derived from the alternative synthetic routes at the earliest stage. At the outset of assessment, all the individual alternative synthetic routes are identified by the graph-theoretic method based on process graphs (P-graphs). Subsequently, the individual alternative synthetic routes are sequentially assessed in descending order of quantifiability, in terms of available energy (or exergy), dissipation, the possible profit, and the toxicity index, respectively. The efficacy of the approach is demonstrated for the manufacture of C 2 H 3 Cl. The approach can possibly be adapted for estimating the sustainability-potential to assess the alternative production routes as represented by alternative flowsheets for manufacturing specific products.
05/2007;
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ABSTRACT: Cell robustness and complexity have been recognized as unique features of biological systems. Such robustness and complexity of metabolic-reaction systems can be explored by discovering, or identifying, the multiple flux distributions (MFD) and redundant pathways that lead to a given external state; however, this is exceedingly cumbersome to accomplish. It is, therefore, highly desirable to establish an effective computational method for their identification, which, in turn, gives rise to a novel insight into the cellular function. An effective approach is proposed for complementarily identifying MFD in metabolic flux analysis and multiple metabolic pathways (MMP) in structural pathway analysis. This approach judiciously integrates flux balance analysis (FBA) based on linear programming and the graph-theoretic method for determining reaction pathways. A single metabolic pathway, with the concomitant flux distribution and the overall reaction manifesting itself as the desired phenotype under some environmental conditions, is determined by FBA from the initial candidate sequence of metabolic reactions. Subsequently, the graph-theoretic method recovers all feasible MMP and the corresponding MFD. The approach's efficacy is demonstrated by applying it to the in silico Escherichia coli model under various culture conditions. The resultant MMP and MFD attaining a unique external state reveal the surprising adaptability and robustness of the intricate cellular network as a key to cell survival against environmental or genetic changes. These results indicate that the proposed approach would be useful in facilitating drug discovery.
Metabolic Engineering 06/2005; 7(3):182-200. · 5.61 Impact Factor
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Liang-Tseng Fan,
Shahram Shafie,
Botond Bertók, Ferenc Friedler,
Dong-Yup Lee,
Hodong Seo,
Sun Won Park,
Sang-Yup Lee,
D.-Y Lee,
H Seo,
S Park,
S Y Lee
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ABSTRACT: Stoichiometrically exact and potentially feasible catalytic or metabolic pathways can be found by synthesizing the networks of plausible elementary or metabolic reac-tions constituting such pathways, respectively. The current contribution presents a mathematically exact algorithmic approach for carrying out the necessary synthesis, which is profoundly complex combinatorially. The approach is based on the unique graph-representation in terms of P-graphs (process graphs), a set of axioms, and a group of combinatorial algorithms. The inclusion or exclusion of a step of each el-ementary or metabolic reaction in the pathway of interest hinges on the general com-binatorial properties of feasible reaction networks. At the outset, a brief overview is given of successful applications to date, followed by an outline of the methodology, on which the approach is based. The approach is illustrated by implementing it to three new examples comprising two catalytic reactions, catalytic combustion of hy-drogen and reduction of nitrogen oxide, and one metabolic reaction, involved in the production of ethanol by yeast. The efficacy of the approach is discussed in light of the results obtained from these examples. Finally, a brief discourse is given of our current and future efforts.
Journal of the Chinese Institute of Engineers. 01/2005; 28:1021-1037.
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ABSTRACT: A highly effective algorithmic method is proposed for optimally synthesizing an azeotropic-distillation system from an extensive set of candidate operating units, i.e., functional units. The method has been derived by resorting to the graph-theoretic approach to process-network synthesis based on process graphs (P-graphs); it also resorts to the methodology established in our previous contribution for dividing the residue curve map (RCM) of a material system, i.e., mixture, to be separated into partitioned materials. This allows the entire space of the RCM to be taken into account in composing networks of candidate operating units, thereby preventing the localization of search. Moreover, the RCM is transformed into the flow-rate map, where any material is quantitatively defined by the molar flow rates of its components instead of the concentrations as in the RCM. This renders it possible to eliminate the nonlinearity in the governing equations of the candidate operating units. The efficacy of the method is amply demonstrated through the well-known example of separating ethanol from its aqueous solution with toluene as the entrainer. The method is applicable to other complex processes with phase transition, and/or phase separation, e.g., crystallization, extraction, reactive distillation, and their combinations.
06/2003;
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Dependable Computing - EDCC-4, 4th European Dependable Computing Conference, Toulouse, France, October 23-25, 2002, Proceedings; 01/2002
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ABSTRACT: Companies rely more and more on the dependability of their e-business application. E-business systems are, by their nature,
heterogeneous, consisting not only of information technology component but also human- and infrastructural resources. Therefore,
the assurance of a proper level of dependability has to cover all aspects of the system. In the paper, a Business Process
Modeling (BPM) based approach is presented, which uses an extended UML profile to design the business processes to compensate
the weaknesses of resources. A fault model describes the typical failure modes of the individual element types. Analysis methodologies
well proven in the field of dependable computing are used to assess the dependability of the system and provide a basis for
countermeasures against the faults. The paper describes the experiences with a pilot application.
12/2001: pages 659-663;
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ABSTRACT: Introduction Diagnostics is one of the core problems in assuring the dependability of complex information technology systems. Nowadays diagnostics does not only a simple activity for identifying faulty hardware resources, but more and more it is a complex activity necessitating to cover both the hardware and software aspects. The increasing frequency of transient errors require more and more sophisticated diagnosis technologies, which also support the subsequent phases of fault handling as well, like damage confinement and reconfiguration. In practice, however one of the basic problems is the proper handling of the high complexity of the diagnostic process. One of the intrinsic assumptions behind all diagnostic algorithms is the notion of a maximum likelihood diagnosis. Frequently this assumption appears simply as "more faults occur with lower frequency than a few ones". Thus, the diagnostics aims at a minimal set of faulty elements compatible with the syndrome. Other approac
03/2001;
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Networks. 01/1998; 31:119-124.
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ABSTRACT: A novel programming framework has been developed for the P-graph-based methodology to provide a standardized software environment for different classes of process-network synthesis (PNS) problems. The P-graph framework has been proven highly successful; its applicability encompasses wide-ranging areas such as reaction-pathway identification, vehicle-routing problems and business-process modeling. A uniform programming paradigm has been proposed here to integrate various available solution engines and interfaces of different types of PNS problems into a single system. A client server architecture with a standardized communication protocol has also been developed, which renders it to be deployable by various client programs with different features, possibly implementable in different programming languages, or adoptable by varied solvers customized for specific problems. Numerous P-graph-based algorithms have been implemented to demonstrate the efficacy of the P-graph framework.
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András Pataricza,
Tamás Bartha,
Botond Bertók,
György Csertán,
Orsolya Dobán, Ferenc Friedler,
János Fülöp,
Gábor Huszerl,
István Majzik,
Ádám Nagy,
László Papp,
Dániel Petri,
Balázs Polgár,
Dániel Varró
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ABSTRACT: Kidolgoztuk a Petri-hálók és produkciós hálók (PNS) egységes szemléletű leírását. Megfogalmaztuk az "optimális trajektória generálásának" problémáját Petri-hálós modellekre. A megoldásként kidolgozott és implementált algoritmus egyúttal temporális logikai követelményeket is vizsgál a modellen. Az algoritmust gyorsítottuk a PNS logikai bázisa fölötti kereséssel. A SPIN modellellenőrzőt magát használva egy másik megoldást is adtunk a problémára, valamint gráftranszformációs rendszerek optimalizálására. Megadtuk a lineáris korlátozási feltételekkel adott szeparábilis konkáv minimalizálási feladat egy elégséges optimalitási kritériumát, mely a Branch-and-Bound típusú algoritmusban használható fel megállási kritériumként. A magasszintű leírásokból a Petri-hálós modellbe történő transzformációkat matematikai alapokon definiáltuk, megvalósításukra automatikus modelltranszformációs megoldást dolgoztunk ki: egy algoritmust, amely GRM profillal adott modellből generálja a Petri-hálót, és egy általános algoritmust, amely UML modellekből származtat a diagnosztika alapjául szolgáló modelleket. Megvizsgáltuk ezen modellek illeszthetőségét a szabványokhoz. Multiprocesszoros rendszerek diagnosztizálására egy PNS technikákat használó algoritmust adtunk, melynek várható hatékonyságát igazoltuk. Munkálatok folytak a diagnosztika tesztalapú megközelítésére, és diagnosztikai modellek kísérletes paraméterezésére. Kísérleteket végeztünk az IBM Holosofx ipari workflow modellező eszköz illesztésére. | A unified treatment for Petri nets and process network (PNS) problems was defined. The 'optimal trajectory generation problem' for Petri nets was defined. Elaboration and implementation of an algorithm that is able not only to give the optimal trajectory but to verify temporal logic requirements for Petri nets. This algorithm was accelerated using Branch-and-Bound method over the logical basis of the feasible process networks. Another algorithm to solve the problem using only the SPIN model checker was elaborated. The optimization of graph transformation systems with time was solved based on the same technique. A sufficient optimality criteria was given for constrained, concave minimization problems. The precise mathematics of the model transformation from high-level models to Petri nets was defined, and automatic model transformations were carried out to realize these transformations: a transformation from UML models given by the GRM profile to Petri nets and a general algorithm that delivers models to diagnose from UML models. The conformancy of these models to standards was investigated. The probabilistic diagnosis problem in multiprocessor systems was solved using PNS techniques. The efficiency of the method was shown. There were efforts to elaborate a test-based approach of diagnostics, and to parameterize diagnostics models based on dependability experiments. Experiments were carried out to transform IBM Holosofx models to Petri nets.
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ABSTRACT: The Fischer–Tropsch synthesis (FTS) for the production of widely distributed hydrocarbons through the catalytic hydrogenation of carbon monoxide (CO) has been intensively and extensively explored. This is attributable to its immense theoretical as well as practical importance. Naturally, such exploration would be greatly facilitated if the feasible or dominant catalytic pathways (mechanisms) of FTS can be determined. The stoichiometrically feasible and independent catalytic pathways (IPi's) of FTS have been exhaustively identified via the rigorous graph–theoretic method based on P-graphs (process graphs). The most extensive set of elementary reactions available, which numbers 26, has yielded 24 IPi's in less than 1 s on a PC. The plausibly dominant pathways have been selected from the stoichiometrically feasible pathways through the analysis of their activation energies. Naturally, the dominant pathway or pathways need ultimately be discriminated among these plausibly dominant pathways via various means, e.g., in situ spectroscopic measurements of intermediates.
Computers & Chemical Engineering.
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ABSTRACT: Manufacturing butanol, ethanol, and acetone through grain fermentation has been attracting increasing research interest. In the production of these chemicals from fermentation, the cost of product recovery constitutes the major portion of the total production cost. Developing cost-effective flowsheets for the downstream processing is, therefore, crucial to enhancing the economic viability of this manufacturing method. The present work is concerned with the synthesis of such a process that minimizes the cost of the downstream processing. At the outset, a wide variety of processing equipment and unit operations, i.e., operating units, is selected for possible inclusion in the process. Subsequently, the exactly defined superstructure with minimal complexity, termed maximal structure, is constructed from these operating units with the rigorous and highly efficient graph-theoretic method for process synthesis based on process graphs (P-graphs). Finally, the optimal and near-optimal flowsheets in terms of cost are identified.
Biotechnology Progress 20(5):1518-27. · 2.34 Impact Factor
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ABSTRACT: Catalytic decomposition of methanol (MD) plays a vital role in hydrogen production, which is the desirable fuel for both proton exchange membrane and direct methanol fuel cell systems. Thus, the catalytic mechanisms, or pathways, of MD have lately been the focus of research interest. Recently, the feasible independent pathways (IPis) have been reported on the basis of a set of highly plausible elementary reactions. Nevertheless, no feasible acyclic combined pathways (APis) comprising IPis have been reported. Such APis cannot be ignored in identifying dominant pathways.
Computers & Chemical Engineering.
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ABSTRACT: The catalytic mechanisms or pathways of water-gas shift (WGS) reaction have been the focus of intense research interest because of its immense importance in hydrogen production. At the outset, 116 stoichiometrically feasible independent pathways (IPi's) have been exhaustively generated within 2 s on a PC through a novel graph-theoretic method based on P-graphs (process graphs) from a set of 17 plausible elementary reactions. This is followed by the determination of IP18 among these 116 stoichiometrically feasible IPi's as the plausibly dominant pathway via energetic analysis.
Journal of the Chinese Institute of Chemical Engineers.
