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Search Results: 1 - 10 of 10639 matches for " Du?an Surla "
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Rules for Evaluation of Scientific Results Published in Scientific Journals
Du?an Surla,Dragan Ivanovi?,Zora Konjovi?,Milo? Rackovi?
International Scientific Journal of Management Information Systems , 2012,
Abstract: This looks into some issues appearing in scientific journals evaluation based on their impact factor (IF). An analysis of the publicly available data on journals’ IFs results in finding that there exist a significant number of journals publication years missing their IF data. Therefore, this article proposes the IF based rules enabling the determination of the journal’s category for the publication years with no IF available. Application of the proposed rules is illustrated through the example of the scientific fields of mathematics, computer science and mechanics. Finally, the examples of the evaluation completed by applying the proposed rules are given. Application of the proposed rules is automated within the CRIS system of the University of Novi Sad (CRIS UNS) using the data available in the database of this system.
Reduction of Single Event Kinetic Models by Rigorous Relumping: Application to Catalytic Reforming Réduction de modèles cinétiques basée sur les événements constitutifs à l’aide d’un regroupement rigoureux : application au reformage catalytique
Cochegrue H.,Gauthier P.,Verstraete J.J.,Surla K.
Oil & Gas Science and Technology , 2011, DOI: 10.2516/ogst/2011122
Abstract: Modeling of refining processes using metal-acid bifunctional catalysts involves an exponentially increasing number of species and reactions, which may rapidly exceed several thousands for complex industrial feedstocks. When building a model for such a process, a priori lumped kinetic models by chemical family do no longer meet the current requirements in terms of simulation details, predictive power and extrapolability. Due to the large number of elementary steps occurring in bifunctional catalysis, it would be quite unrealistic to manually build a detailed kinetic network of this scale. Hence, computer generation of the reaction network according to simple rules offer an elegant solution in such a case. Nevertheless, it remains difficult to determine and solve the kinetic equations, mainly due to the lack of analytical detail required by a detailed model. For several refining processes, however, reasonable assumptions on the equilibria between species allow to perform an a posteriori relumping of species, thus reducing the network size substantially while retaining a kinetic network between lumps that is strictly equivalent to the detailed network. This paper describes a network generation tool and the a posteriori relumping method associated with the single-event kinetic modeling methodology. This a posteriori relumping approach is illustrated for and successfully applied to the kinetic modeling of catalytic reforming reactions. La modélisation des procédés de raffinage utilisant des catalyseurs bifonctionnels métal-acide fait intervenir un nombre exponentiellement croissant d'espèces et de réactions qui peut rapidement dépasser plusieurs milliers pour des charges industrielles complexes. Lors de la réalisation d'un modèle de procédé, l'utilisation de modèles cinétiques de regroupement a priori par familles chimiques ne satisfait plus les besoins actuels de simulation détail- lée, de prédictivité et d'extrapolabilité. à cause du grand nombre d'étapes élémentaires impliquées dans la catalyse bifonctionnelle, il est déraisonnable de vouloir construire à la main un réseau cinétique détaillé d'une telle ampleur. La génération informatique du réseau réactionnel à partir de règles simples propose une solution élégante dans un tel cas. Malgré cela, l'établissement des équations cinétiques et leur résolu- tion reste difficile, essentiellement à cause du manque de détail analytique demandé par un modèle détaillé. Néanmoins, pour plusieurs procédés de raffinage, des hypothèses raisonnables concernant les équilibres entre espèces permettent d'effectuer un regrou
Kinetic Modeling using the Single-Event Methodology: Application to the Isomerization of Light Paraffins Modélisation cinétique basée sur la méthodologie des événements constitutifs : application à l’isomérisation des paraffines légères
Surla K.,Guillaume D.,Verstraete J.J.,Galtier P.
Oil & Gas Science and Technology , 2011, DOI: 10.2516/ogst/2011119
Abstract: The construction of kinetic models is an important step in the development of refining processes. Indeed, these models can be used to predict the performances of the process, to optimize the operation of a unit and to optimally design a reactor and the associated process (choice of the reactor configuration, determination of optimal operating conditions, use of recycles, etc.). The current demand for models is particularly focused towards the development of detailed predictive models that are able to account for significant changes in process operation. Hence, they need to allow for the extrapolation to considerably different operating conditions or to very diverse feedstocks. Kinetic modeling based on the single-event theory meets these requirements, since it allows detailed prediction of the composition, and hence the yield structure from the reactors. The single-event theory was initially developed for the radical chemistry occurring during thermal cracking [Clymans et Froment (1984) Comput. Chem. Eng. 8, 2, 137-142; Hillewaert et al. (1988) AIChE J. 34, 1, 17-24; Willems et Froment (1988a) Ind. Eng. Chem. Res. 27, 11, 1959-1966; Willems et Froment (1988b) Ind. Eng. Chem. Res. 27, 11, 1966-1971], later extended to acid catalysis [Baltanas et Froment (1985) Comput. Chem. Eng. 9, 1, 71-81; Baltanas et al. (1989) Ind. Eng. Chem. Res. 28, 899-910; Vynckier et Froment (1991) Modeling of the kinetics of complex processes upon elementary steps, in Kinetic and thermodynamic lumping of multicomponent mixtures, Astarita G., Sandler S.I. (eds), Elsevier Science Publishers BV, Amsterdam, pp. 131-161], and recently adapted to metal catalyzed processes [Lozano-Blanco et al. (2006) Oil Gas Sci. Technol. 61, 4, 489-496; Lozano- Blanco et al. (2008) Ind. Eng. Chem. Res. 47, 16, 5879-5891]. This methodology developed in the “Laboratorium voor Petrochemische Techniek” at Ghent University consists in constructing a reaction network which, although exhaustive, is described by a limited number of independent kinetic parameters. The behavior of complex feedstocks can therefore be predicted based on studies conducted on model molecules. This method is applied at IFP Energies nouvelles to several refining processes. The purpose of this article is to describe this methodology in a detailed manner and to present its application to the isomerization of C5-C6 paraffins. L’établissement de modèles cinétiques est une étape importante du développement de procédés de raffinage. En effet, ces modèles peuvent être utilisés pour prédire les performances du procédé, pour optimiser l’opér
Single Event Kinetic Modelling without Explicit Generation of Large Networks: Application to Hydrocracking of Long Paraffins Modélisation cinétique par événements constitutifs sans génération explicite de grands réseaux : application à l’hydrocraquage des paraffines longues
Guillaume D.,Valéry E.,Verstraete J.J.,Surla K.
Oil & Gas Science and Technology , 2011, DOI: 10.2516/ogst/2011118
Abstract: The single event modelling concept allows developing kinetic models for the simulation of refinery processes. For reaction networks with several hundreds of thousands of species, as is the case for catalytic reforming, rigorous relumping by carbon atom number and branching degree were efficiently employed by assuming chemical equilibrium in each lump. This relumping technique yields a compact lumped model without any loss of information, but requires the full detail of an explicitly generated reaction network. Classic network generation techniques become impractical when the hydrocarbon species contain more than approximately 20 carbon atoms, because of the extremely rapid growth of reaction network. Hence, implicit relumping techniques were developed in order to compute lumping coefficients without generating the detailed reaction network. Two alternative and equivalent approaches are presented, based either on structural classes or on lateral chain decomposition. These two methods are discussed and the lateral chain decomposition method is applied to the kinetic modelling of long chain paraffin hydroisomerization and hydrocracking. The lateral chain decomposition technique is exactly equivalent to the original calculation method based on the explicitly generated detailed reaction network, as long as Benson’s group contribution method is used to calculate the necessary thermodynamic data in both approaches. Le concept de modélisation par événements constitutifs permet de développer des modèles cinétiques pour la simulation des procédés de raffinage. Pour des réseaux réactionnels de centaines de milliers d'espèces, comme cela est le cas pour le reformage catalytique, le regroupement rigoureux par nombre d'atomes de carbone et degré de ramification a été utilisé efficacement en faisant l'hypothèse de l'équilibre chimique dans chaque groupe. Cette technique de regroupement conduit à un modèle regroupé compact sans perte d'information, mais nécessite tous les détails d'un réseau réactionnel complet, généré de manière explicite. Les techniques classiques de génération de réseaux deviennent inutilisables quand les hydrocarbures contiennent au delà d'environ 20 atomes de carbone à cause de la croissance extrêmement rapide du réseau réactionnel. Ainsi, des techniques implicites de regroupement ont été développées afin de calculer les coefficients de regroupement sans avoir à générer le réseau réactionnel détaillé. Deux approches alternatives et équivalentes sont présentées, basées soit sur une décomposition en classes structurales, soit une décomposition en ch
Extension of the Single-Event Methodology to Metal Catalysis: Application to Fischer-Tropsch Synthesis Extension de la méthodologie des événements constitutifs à la catalyse métallique : Application à la synthèse Fischer-Tropsch
Lozano-Blanco G.,Surla K.,Thybaut J.W.,Marin G.B.
Oil & Gas Science and Technology , 2010, DOI: 10.2516/ogst/2009075
Abstract: The single-event methodology has been extended to metal catalysis using Fischer-Tropsch synthesis on an iron-based catalyst as case study. The reaction mechanism has been assessed in terms of elementary steps that could be categorized in reaction families such as reductive elimination, β-hydride elimination and methylene insertion. A computer code has been developed for the generation of the reaction network containing these elementary steps. The representation of reacting and intermediate species explicitly takes into account metal-carbon bonds as well as the presence of oxygen. The model has been validated using iron-based catalytic data at 623 K, 0.6 to 2.1 MPa, inlet molar H2/CO ratio between 2 and 6. 14 parameters, among which 10 activation energies and 4 atomic chemisorption enthalpies have been adjusted to the experimental data. Experimentally observed trends in alkane and 1-alkene product yields with the carbon number were adequately reproduced as well as the individual molar yields of the non-hydrocarbon products. La méthodologie par événements constitutifs a été étendue à la catalyse métallique en utilisant la synthèse Fischer-Tropsch sur un catalyseur au fer comme cas d'étude. Le mécanisme réactionnel a été décomposé en étapes élémentaires qui peuvent être classées par type de réactions, telles que l'élimination réductrice, l'élimination d'hydrure en β, et l'insertion de groupe méthylène. Un code de calcul a été développé pour générer le réseau réactionnel impliquant ces étapes élémentaires. La représentation des réactifs et des espèces intermédiaires prend en compte explicitement les liaisons carbone-métal et inclut la présence d'atomes d'oxygène. Le modèle a été validé sur une base de données obtenues sur un catalyseur à base de fer à 623 K, sur une plage de 0,6 à 2,1 MPa, un ratio H2/CO en entrée variant de 2 à 6. Quatorze paramètres, dont 10 énergies d'activation et 4 enthalpies de chimisorption atomique ont été ajustés aux données expérimentales. Les tendances observées expérimentalement pour les rendements en alcanes et alcènes-1 en fonction du nombre de carbones sont correctement reproduites, ainsi que les rendements molaires des produits non-hydrocarbures.
Cold-State Investigation on a Flame Holder  [PDF]
Yiqing Du
Journal of Power and Energy Engineering (JPEE) , 2013, DOI: 10.4236/jpee.2013.17008
Abstract:

Slitty bluff body is widely used as a high-performance flame holder in power industry. To understand the flame stability mechanism, the evolution of the near wake over a slitty bluff body in cold state was numerically investigated using the renormalization group (RNG) k-ε model at Reynolds number of 470,000. The coherent structure of the near wake was identified by the vortex shedding simulation. To explain the vortex shedding, a mechanism that single vortex of large size suddenly immerses two shear layers was proposed. To quantitatively compare the near wakes at different gap ratio, a vortex shedding character dimension was first proposed. This character dimension has positive correlation with flame stability. Particle-image velocimetry (PIV) measurements in a close wind tunnel were also carried out to confirm the observation from the numerical study. The evidence shows that the numerical results are of good agreement with the cold-state experiments.

Classification of Single Traveling Wave Solutions to the Generalized Strong Nonlinear Boussinesq Equation without Dissipation Terms in P = 1  [PDF]
Xinghua Du
Journal of Applied Mathematics and Physics (JAMP) , 2014, DOI: 10.4236/jamp.2014.23006
Abstract:

By the complete discrimination system for polynomial method, we obtained the classification of single traveling wave solutions to the generalized strong nonlinear Boussinesq equation without dissipation terms in p=1.

New Fixed Point Theorems of Mixed Monotone Operators  [PDF]
Xinsheng Du
Applied Mathematics (AM) , 2014, DOI: 10.4236/am.2014.53037
Abstract:

Mixed monotone operator is an important nonlinear operator. It exists extensively in the research of nonlinear differential and integral equations. Generally, the research of mixed monotone operators in partially ordered Banach spaces requires compactness, continuity or concavity-convexity of the operators. In this paper, without any compact and continuous assumption, we obtain some new existence and uniqueness theorems of positive fixed point of e-concave-convex mixed monotone operators in Banach spaces partially ordered by a cone, which extends the existing corresponding results.

Existence of Positive Solutions to Semipositone Fractional Differential Equations  [PDF]
Xinsheng Du
Applied Mathematics (AM) , 2016, DOI: 10.4236/am.2016.714127
Abstract: In this paper, by means of constructing a special cone, we obtain a sufficient condition for the existence of positive solution to semipositone fractional differential equation.
A Literature Review on Institutional Environment and Technological Innovation  [PDF]
Zhuoyan Du
American Journal of Industrial and Business Management (AJIBM) , 2018, DOI: 10.4236/ajibm.2018.89130
Abstract: This article is a literature review on institutional environment and technology innovation. The author discusses the origin and classification of the institutional environment, has a through understanding of the institutional environment, and examines studies about institutional environment and technology innovation from different perspectives to reach some constructive suggestions to better promote technology innovation.
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