bluuebunny/crossref_metadata_2025_split huggingface dataset:
Mathematical modeling and steady‐state analysis of a scheibel extraction column
Authors: Alatiqi I. , Aly G. , Mjalli F. , Mumford C. J. 
Published: March 2009

AbstractThe steady‐state behavior of a nine‐stage Scheibel extraction column was modeled and simulated using a back flow stagewise model. Steady‐state experiments were conducted, using the system water‐acetone‐toluene, for three phase ratios and three agitator speeds. The mathematical model was validated with the experimental concentration profiles by a single parameter fitting technique with an unconstrained optimization algorithm.Steady‐stage analysis of the experiments was performed for a further control study. The calculated steady‐state gain matrices were used for interaction analysis using different steady‐state analysis methods, e.g. Bristol numbers, Condition numbers, Morari Indexes of Integral Controllability, and Niederlinski Indexes. The results indicate that both agitator speed and phase ratio have a substantial influence on the control structure. Dynamic analysis should therefore be performed to verify the optimum control method for this process.
Estimation of equation of state parameters for 1,1,1,2‐tetrafluoroethane in a modified benedict‐webb‐rubin equation
Authors: Sörner Maria , Ström Krister H. U. 
Published: March 2009

AbstractThermodynamic properties of refrigerants are of great importance in the design and simulation of heat pumps and refrigeration units. The parameter values in the modified Benedict‐Webb‐Rubin equation of state proposed by Lee and Kesler (1975) have been determined for HFC 134a with the Error‐in‐Variables Model. The types of data used for the parameter estimation have been: pressure‐volume‐temperature data for subcooled and superheated conditions, vapour pressures, saturated vapour and liquid volumes, isobaric arid isochoric heat capacities and second virial coefficients. Calculations carried out with the equation of state according to Lee and Kesler, with the parameters here proposed, agree well with experimental data for the fluid.
Contrǒle hydrodynamique en convection mixte de l'épaisseur de dépǒts en phase gazeuse de semi‐conducteurs sur des corps à symétrie de révolution
Authors: Cherif A. Ali , Daïf A. , Rakotomalala M. , Daguenet M. 
Published: March 2009

AbstractLes auteurs résolvent à l'aide d'une méthode aux différences finies les équations de la couche limite laminaire et permanente qui entoure des corps à symétrie de révolution (sphère, ellipsoïdes allongé et aplati), au nez orienté vers le haut, portés, à 500°C, en rotation uniforme autour d'un axe vertical dans un écoulement axial descendant de gaz d'hydrogène à 25°C. La variabilité des propriétés physiques; du fluide en fonction de la température est prise en compte ainsi que la convection naturelle qui en résulte. Les auteurs montrent que l'écoulement et les transferts dépendent de façon significative de cette variabilité et qu'il est possible de contrǒler la croissance des couches limites thermique et massique en agissant sur les conditions opératoires, notamment sur le profil des corps. Une application directe de ce travail est le contrǒle des dépǒts en phase vapeur.
Optimum dimensions of longitudinal rectangular fins and cylindrical pin fins with variable heat transfer coefficient
Authors: Yeh Rong‐Hua 
Published: March 2009

AbstractConsidering a temperature dependent heat transfer coefficient, the optimum dimensions of longitudinal rectangular fins and cylindrical pin fins have been investigated analytically. Employing the parameters of fin thickness or fin diameter and tip temperatures, the optimum dimensions, heat dissipation, and efficiency of fins are obtained by Lagrange's multiplier method. It is shown that the fin efficiency of an optimum cylindrical pin fin is higher than that of an optimum rectangular fin. To facilitate the thermal design of the heat transfer components, very simple mathematical expressions for the optimum dimensions of fins are presented in this study.
Mathematical modelling of the transient behaviour of cstrs with reactive particulates: Part 1 — The population balance framework
Authors: Rubisov Dmitri H. , Papangelakis Vladimiros G. 
Published: March 2009

AbstractThe population balance model appears to be the best approach to model particulate systems where multiple heterogeneous reactions occur. This work demonstrates a mathematical formulation that is based on the population balance model, and aims at simulating the non steady‐state behaviour of a single‐stage CSTR under isothermal operation. The chemical reaction system is a typical example from the field of hydrometallurgy with two parallel reactions, one being leaching, the other precipitation with simultaneous reactant regeneration. The solution of the resulting system of the partial and ordinary differential equations is achieved by combining the moment transformation of the population balance equations with the numerical method of lines, using the Mathematica® software. Finally, examples are given for a reactor startup in two cases: a single leaching reaction, and simultaneous leaching and precipitation reactions. In the first case, the difference between simultaneous and sequential feeding in achieving steady‐state is also discussed.
Kinetics of acetic acid esterification over ion exchange catalysts
Authors: Xu Z. P. , Chuang K. T. 
Published: March 2009

AbstractComputer simulation showed that catalytic distillation is an attractive process for the removal of dilute acetic acid from wastewater. Selection of catalysts and kinetic data have been obtained for the design of the catalytic distillation column.Kinetic measurements were conducted in a batch reactor. Methanol was added to the dilute acetic acid solutions and reacted with the acid in water to form methyl acetate and water. The reaction can be catalyzed by solid acid catalysts. It was found that Amberlyst 15 was an effective catalyst for this reaction. The effects of stirrer speed, reaction temperature, reactant concentration and catalyst loading on reaction rate were investigated. A complete kinetic equation for describing the reaction catalyzed by Amberlyst 15 was developed. This equation can be used in the simulation and design of the catalytic distillation column for removing acetic acid from wastewater.
Unsteady states in metallurgical sulphuric acid plants after SO2 concentration drop in the feed gas
Authors: Gosiewski Krzysztof 
Published: March 2009

AbstractThe paper presents results of dynamic mathematical model simulations for selected two characteristic flowsheets of metallurgical SO2 oxidation plant after temporary decrease of reactant concentration in the feed gas. An analysis of dynamic resistance of the plant for the concentration drop, from the point of view of the dynamic autothermal properties is given.
Transient and resonant behavior for no reduction by CO over a Pt/Al2O3 catalyst during forced composition cycling
Authors: Sadhankar Ramakant R. , Lynch David T. 
Published: March 2009

AbstractThe reduction of NO by CO over a Pt/Al2O3 catalyst has been investigated using the technique of forced concentration cycling in an isothermal recycle reactor at 485 K. Time‐average conversions exhibit resonant behavior with increasing frequency. Maximum time‐average NO conversion of 78%, compared with the steady‐state conversion of 3.8%, was attained during out‐of‐phase feed concentration cycling. The effect of the phase angle between the NO and CO feed cycles has been examined. Higher conversions are obtained by decreasing the NO phase lead below 180°. The convergence to cycle‐invariance was slow for high frequency cycling.
Sorbent development for continuous regenerative H2S removal in a rotating monolith reactor
Authors: Bakker WridzerJ. W. , Vriesendorp Maaike , Kapteijn Freek , Moulijn Jacob A. 
Published: March 2009

AbstractA high capacity and regenerable manganese based sorbent for desulfurization of hot dry fuel gas from coal gasification has been developed. Pure γ‐Al2O3 and washcoated cordierite monoliths impregnated with manganese acetate and calcined at 973 K resulted in highly dispersed Mn3O4 on γ‐Al2O3. MnS was formed during sulfidation and MnAl2O4 during subsequent regeneration with steam. The optimal operation temperature was found to be between 1123 and 1223 K. The maximum capacity of the acceptor was 17 mass% sulfur which was obtained for a 32 mass% manganese loading. A deactivation test of 65 subsequent sulfidation and regeneration cycles showed minor deactivation during the first cycles followed by a stable performance.This sorbent will be used in a rotating monolith reactor in which absorption and regeneration takes place simultaneously in separate sections, which enables a continuous operation.
Energy trapping during reverse flow operation with discrete power introduction: Experiments and theory
Authors: Snyder Jon D. , Subramaniam Bala 
Published: March 2009

AbstractIt is shown that reverse flow operation is well‐suited for packed‐bed operation requiring energy addition from sources external to the packing. Packed‐bed temperature profiles are dictated by (a) how the power is distributed axially, and (b) the temperature‐profile movement, proportional to the volume of flowing gas introduced during the semicycle (flow rate × semicycle period). While peak‐shaped temperature profiles result for energy input at axially central locations, plateau‐shaped temperature profiles result for energy distribution offset from the center and for relatively large volumes of gas introduced during a semicycle. In both cases, however, efficient energy integration is achieved with the maximum temperature rise being hundreds of degrees greater than the adiabatic temperature rise for unidirectional flow operation.
Choosing the right model: Case studies on the use of statistical modeldiscrimination experiments
Authors: Burke A. L. , Duever T. A. , Penlidis A. 
Published: March 2009

AbstractStatistical model discrimination methods were developed to efficiently and reliably choose the ‘best’ model for a system from a set of candidate models. Three promising model discrimination techniques are compared using three chemical engineering examples in this paper. The examples were studied via computer simulations in which experimental data were generated using a known model. The use of a computer simulation allowed factors such as error magnitude to be studied at different levels in repeat runs of the program. The results indicated the exact entropy method is the best method for use with non‐nested nonlinear models, while the Buzzi‐Ferraris and Forzatti (1983) method is best for use with nonlinear nested models.
Kinetics of the dissolution of silica in aqueous sodium hydroxide solutions at high pressure and temperature
Authors: Jendoubi F. , Mgaidi A. , El Maaoui M. 
Published: March 2009

AbstractThe kinetic of the reaction of sand with aqueous NaOH corresponding to the ratio SiO2/Na2O = 2 was studied in a pressure vessel at 220°C and 2.7 MPa. Since the kinetic curves could not be obtained directly from the experimental data, a new method is proposed to plot the entire kinetic graph from experimental data. An analytical expression of the type α = A [1 ‐exp(‐Bt)] describes the system perfectly. The constants A and B were calculated for a silica sample having a narrow granulometric distribution (range i.e. 300–315 μm). The value of A is found to be almost constant, between 0.95 to 0.99 and B ranges from 0.03 to 0.14 when [OH‐] increases from 0.5 to 12.5 mol/L. The kinetic order with respect to OH− is equal to 0.470 + 0.013 and the kinetic constant at 220°C is 3.933 × 10−6 g/m2.s.
Solid‐liquid mass transfer coefficients in gas‐solid‐liquid agitated vessels
Authors: Grisafi Franco , Brucato Alberto , Rizzuti Lucio 
Published: March 2009

AbstractThe research on mass transfer coefficients in solid‐liquid agitated systems has received substantial attention in the past, due both to the interest in fundamental aspects of mass transfer between particles and turbulent fluids and to the importance of practical applications. In contrast, little information is available on solid‐liquid mass transfer when a third gaseous phase is also dispersed into the system, in spite of the importance of the applications of gas‐solid‐liquid agitated systems. In this work a suitable dissolution technique was used to measure the solid‐liquid mass transfer coefficient in gas‐solid‐liquid vessels stirred by either radial or axial impellers. The mechanical power dissipated by the stirrers at various agitation speeds and gas flow rates was also measured by means of a new technique. The mass transfer data obtained were found to be well correlated to the 0.25 power of the specific power dissipation, indicating that the Kolmogorov's theory of mass transfer applies to these systems, while no clear influence of the gas hold‐up was ascertained.
A hybrid expert‐procedural system for the design of reverse‐osmosis desalination plants
Authors: Voivontas Dimosthenis , Papafotiou Kostas , Assimacopoulos Dionysis , Mitsoulis Evan 
Published: March 2009

AbstractThe problem of computer‐aided design and synthesis of a reverse‐osmosis desalination plant is presented. A hybrid expert‐procedural system has been developed that deal with the synthesis problem at two levels of abstraction. The expert part of the system uses qualitative data, and through heuristics, makes decisions about the structure of the plant. The procedural part of the system uses the decisions of the expert part as a basis for detailed design and optimisation. The heuristics used in the expert part come from experienced designers and from proposals of membrane manufacturers. The detailed calculations are based on mass balance equations and correlations for the permeators. The system developed can be used to propose a reverse‐osmosis plant structure and to perform detailed calculations for possible design scenarios envisaged by the user. A case study on such a plant is also given and shows how the expert system handles the design problem of a reverse osmosis desalination plant.
Drying of soybean seeds in a crossflow moving bed
Authors: Barrozo Marcos A. S. , Henrique Humberto M. , Sartori Dermeval J. M. , Freire José T. 
Published: March 2009

AbstractThe aim of this work was to investigate simultaneous heat and mass transfer between air and soybean seeds in a crossflow moving bed dryer. A model was developed from mass and energy conservation applied to the fluid and particulate phases. The equilibrium, heat transfer and mass transfer equations were taken from studies published earlier. Equations for drying kinetics were obtained from a thin layer study, and the equilibrium equation was chosen from rival model discrimination based on nonlinearity measures. The experimental part of this work involved the determination of air temperature distribution, grain moisture through the bed and air humidity at the bed outlet. The model equations were discretized by orthogonal collocation in the air flow direction. The resulting differential‐algebraic equations were solved using a method based on backward differential formulas. Simulation results showed good agreement with experimental data.
Iron—molybdenum—oxide catalysts for selective oxidation of hydrogen sulfide to sulfur
Authors: Li Kuo‐Tseng , Huang Chun‐Hsiung 
Published: March 2009

AbstractThe selective oxidation of hydrogen sulfide to sulfur was studied over iron‐molybdenum oxides with various Fe‐Mo ratios. Strong synergistic phenomenon in catalytic activity was observed for the Fe‐Mo‐O binary oxides. Under identical reaction conditions, the areal rates of the binary oxides were superior to those of the corresponding single oxide catalysts, which suggest that the new compound Fe2(MO4)3 formed in the binary oxide is more active than Fe2O3 and MoO3. The oxidation rates of H2S were found to exhibit first‐order dependence on the hydrogen sulfide concentration, which implies that the activation of H2S is the rate‐limiting step.
Power draw of a high‐Shear homogenizer
Authors: Myers Kevin J. , Reeder Mark F. , Ryan David 
Published: March 2009

AbstractThe power draw of a high‐shear rotor‐stator homogenizer has been characterized in laminar, transitional, and turbulent operation. The power draw is comprised of two components — that associated with mixing and that associated with a bushing and bearings in the device. In turbulent operation, the mixing power draw is influenced primarily by pumping mode (up‐ or down‐pumping), and to a lesser extent, by vessel baffling and other geometric parameters. Mixing power draw can be characterized in terms of power number across the Reynolds number spectrum if an empirical Froude number correction is applied.
An update on the genotoxicity and carcinogenicity of marketed pharmaceuticals with reference to in silico predictivity
Authors: Snyder Ronald D. 
Published: March 2009

AbstractInformation from the 1999 through 2008 Physicians' Desk Reference (PDR) was used to evaluate the genotoxicity of marketed drugs. Where available, data regarding the rodent carcinogenicity results were included (PDR and Gold potency database). In addition, computational predictivity of genotoxicity (DEREK, MC4PC) is included and expanded upon from two previous reviews. The present paper contains genotoxicity data on 545 marketed drugs. Excluded from analysis were most cytotoxic anti‐cancer and antiviral drugs, nucleosides (all with known mechanistic genotoxicity), steroids with class‐specific genotoxicity and biologicals or peptide‐based drugs. Per assay type, the percentage of positive drugs was: Bacterial mutagenesis assay: 38/525 (7.1%), in vitro chromosome aberrations: 88/380 (26.1%); mouse lymphoma assays (MLA): 32/163 (19.1%), in vivo cytogenetics: 49/438 (11.1%). The relationship among positive genetic toxicity findings, rodent carcinogenicity, and in silico prediction is discussed. Finally, supporting evidence is presented for the idea that the presence of an N‐dialkyl group or piperidine aryl ketone may somehow be associated with genotoxicity, perhaps through DNA intercalation and consequent DNA topoisomerase II inhibition. Environ. Mol. Mutagen. 2009. © 2009 Wiley‐Liss, Inc.
Steady‐state priors for vector autoregressions
Authors: Villani Mattias 
Published: March 2009

AbstractBayesian priors are often used to restrain the otherwise highly over‐parametrized vector autoregressive (VAR) models. The currently available Bayesian VAR methodology does not allow the user to specify prior beliefs about the unconditional mean, or steady state, of the system. This is unfortunate as the steady state is something that economists usually claim to know relatively well. This paper develops easily implemented methods for analyzing both stationary and cointegrated VARs, in reduced or structural form, with an informative prior on the steady state. We document that prior information on the steady state leads to substantial gains in forecasting accuracy on Swedish macro data. A second example illustrates the use of informative steady‐state priors in a cointegration model of the consumption‐wealth relationship in the USA. Copyright © 2009 John Wiley & Sons, Ltd.
Doxycycline enhances the Ras‐MAPK signaling and proliferation of mouse thymic epithelial cells
Authors: Chen Xun , Xia Sheng , Li Rong , Liu Hui , Huang Ying , Qian Xiaoping , Xiao Xueyuan , Xu Xun , Lin Xin , Tian Yuxiang , Zong Yangyong , He Dacheng , Chen Weifeng , Zhang Yu , Shao Qixiang 
Published: March 2009

AbstractDepletion of T‐cell‐dependent immunity is a major consideration for patients suffering from infections of human immunodeficiency virus (HIV), those undergoing organ transplantation, and those receiving anti‐cancer chemotherapy and/or radiotherapy. In general, T‐cell regeneration occurs in the thymus through thymopoiesis. We have found that doxycycline (Dox), a tetracycline derivative, enhances the proliferation of mouse thymic epithelial cells, which are unique in their capacity to support positive selection and are essential throughout the development of thymocytes. Cell cycle analysis indicates that the increased cell proliferation is due to a shortened G0/G1 phase. To reveal the underlying mechanisms, we examined the expression of an array of molecules that regulate the cell cycle. The results show that in mouse thymic medullary‐type epithelial cell line 1 (MTEC1) Dox leads to elevated levels of H‐Ras, phosphorylated extracellular signal‐regulated kinase 1/2 (p‐ERK1/2), cyclin E, cyclin dependent kinase 4/2 (CDK4/CDK2), E2F3, and c‐myc. These data, and the observation that the proliferation‐enhancing effect is largely abolished following treatment with an ERK inhibitor support an active role of the Ras‐ERK/mitogen‐activated protein kinase (MAPK) signaling pathway. In conclusion, the present study reveals a new activity of an old family of antibiotics. The in vivo effect of Dox on immune reconstitution warrants further exploration. J. Cell. Biochem. 107: 494–503, 2009. © 2009 Wiley‐Liss, Inc.
High‐resolution narrowband CARS spectroscopy in the spectral fingerprint region
Authors: Chimento P. F. , Jurna M. , Bouwmans H. S. P. , Garbacik E. T. , Hartsuiker L. , Otto C. , Herek J. L. , Offerhaus H. L. 
Published: March 2009

AbstractCoherent anti‐Stokes Raman scattering (CARS) spectroscopy is an important technique for spectroscopy and chemically selective microscopy, but wider implementation requires dedicated versatile tunable sources. We describe an optical parametric oscillator (OPO) based on a magnesium oxide‐doped periodically poled lithium niobate crystal, with a novel variable output coupler, used as a tunable coherent light source. The OPO's signal wavelength ranges from 880 to 1040 nm and its idler wavelength from 1090 to 1350 nm.We use this OPO to demonstrate high‐resolution narrowband CARS spectroscopy on bulk polystyrene from 900 to 3600 cm−1, covering a large part of the molecular fingerprint region. Recording vibrational spectra using narrowband CARS spectroscopy has several advantages over spontaneous Raman spectroscopy, which we discuss. We isolate the resonant part of the CARS spectrum and compare it to the spontaneous Raman spectrum of polystyrene using the maximum entropy method of phase retrieval; we find them to be in extremely good agreement. Copyright © 2009 John Wiley & Sons, Ltd.
Preparation of polyaniline/vermiculite clay nanocomposites by in situ chemical oxidative grafting polymerization
Authors: Tang Zhaobin , Liu Peng , Guo Jinshan , Su Zhixing 
Published: March 2009

AbstractBACKGROUND: Recently, conducting polymers have attracted much attention, since they have interesting physical properties and many potential applications, such as in conductive coating charge storage. Hence the synthesis of conducting polymer nanocomposites is also an area of increasing research activity.RESULTS: Vermiculites (VMTs) were successfully delaminated using an acid treatment. Polyaniline (PANI)/VMT nanocomposites were prepared by in situ chemical oxidative grafting polymerization.CONCLUSION: The chemical grafting of PANI/VMTs was confirmed by Fourier transform infrared and UV‐visible spectroscopy. The percentage of grafted PANI was 142.7 wt% as a mass ratio of the grafting PANI and charged nano‐VMTs, investigated using thermogravimetric analysis. In addition, characteristic agglomerate morphology of PANI was observed in the composites using scanning electron microscopy. Thermal analyses indicated that the introduction of VMT nanosheets had a beneficial effect on the thermal stability of PANI. The electrical conductivity of the nanocomposites was 3.9 × 10−3 S cm−1, a value typical for semiconductors. Copyright © 2009 Society of Chemical Industry