bluuebunny/crossref_metadata_2025 huggingface dataset:
Gas‐liauid mass transfer in non‐newtonian fluids in a tank stirred with a helical ribbon screw impeller
Authors: Tecante A. , Choplin L.
Published: March 2009

Oxygen transfer in aqueous solutions of CMC, xanthan gum, and polyacrylamide in a vessel equipped with a helical ribbon screw impeller and a multi‐orifice ring sparger was studied. The KLa values obtained were comparable to those reported for radial flow impellers, but they are more representative of the oxygen transfer in the bulk of the liquid because of a more homogeneous mixing and absence of dead zones. Dimensionless correlations including the effect of the physical properties of the fluids, and those of operating conditions were developed. A dimensionless correlation for each fluid is proposed.
Benzyl diethyl phosphite as a coke inhibitor during naphtha pyrolysis. tubular reactor studies
Authors: Chowdhury S. N. , Kunzru D.
Published: March 2009

The effectiveness of benzyl diethyl phosphite as a coke inhibitor during naphtha pyrolysis was investigated in a tubular reactor at 1073 K and atmospheric pressure. Significant reduction in the coking rate was achieved by adding benzyl diethyl phosphite to the feed. The effect of toluene, methylcyclohexane, l‐octene and carbon disulfide on the rate of coke formation was also investigated. Toluene enhanced the rate of coke formation significantly, whereas with methylcyclohexane and l‐octene the increase was less appreciable. Carbon disulphide decreased the amount of coke deposited initially, but with increasing run time the asymptotic coking rates were found to be higher than for straight‐run naphtha. The yields of propylene, 1,3‐butadiene and butenes increased on addition of carbon disulphide.
Analytical effectiveness factor calculations concerning product‐inhibited fermentations associated with biofilm growth and maintenance
Authors: Vanede C. J. , Bollen A. M. , Beenackers A. A. C. M.
Published: March 2009

An analytical reaction engineering model, recently presented by van Ede et al. (1992), which describes formation of inhibiting products associated with the growth of immobilized biofilms, is extended to describe simultaneous production associated with biofilm maintenance. The model accounts for both the metabolic rate controlling behaviour of an inhibitory product in the biofilm, and the effect of diffusion limitation in the transport of this product or a substrate, on the biofilm thickness.

Simple criteria are presented to check the applicability of the model in the case of true Monod kinetics.

As a potentially industrially important example, ethanol production by Zymomonas mobilis is treated.
Extension of hála's model to correlate isobaric vapor‐liquid equilibria containing calcium chloride
Authors: Kumagae Yoshio , Arai Yasuhiko
Published: March 2009

Isobaric vapor‐liquid equilibria (VLE) of methanol‐water and methanol‐ethanol systems with calcium chloride at several concentrations were studied from the view point of the applicability of Hála's model which had been applied to correlate isothermal VLE of salt‐containing systems. Prediction of the VLE of the two isobaric systems was not satisfactory with the binary interaction parameters taken from the corresponding isothermal systems because of the different temperature range. However, it was found that the correlation of the isobaric systems was successful by adjusting solvent‐salt parameters. It was also found that the parameters obtained were independent of the salt concentration.
Prediction of carbon dioxide gas hydrate formation conditions in aqueous electrolyte solutions
Authors: Tse C. W. , Bishnoi P. R.
Published: March 2009

A methodology for predicting the incipient equilibrium conditions for carbon dioxide gas hydrates in the presence of electrolytes such as NaCl, KCl and CaCl2 is presented. The method utilizes the statistical thermodynamics model of van der Waals and Platteeuw (1959) to describe the solid hydrate phase. Three different models were examined for the representation of the liquid phase: Chen and Evans (1986), Zuo and Guo (1991), and Aasberg‐Petersen et al. (1991). It was found that the model of Zuo and Guo (1991) gave the best results for predicting incipient CO2 gas hydrate conditions in aqueous single salt solutions. The model was then extended for prediction of CO2 gas hydrates in mixed salts solutions. The predictions agree very well with experimental data.
Synthesis of entrainers in heteroazeotropic distillation systems
Authors: Furzer I. A.
Published: March 2009

Group contribution methods have been used to synthesise entrainers in the series, n‐alkanes, aromatics, cycloalkanes and branched alkanes. The separation of ethanol from the synthesised entrainers depends on the size of a loop on the thermodynamic x‐y diagram. Very easy separations are possible with hexane and 2,2‐dimethylbutane, leading to high purity ethanol. A set of heuristic rules is proposed as a knowledge database to assist expert systems to identify the optimal entrainer.
Modified oil agglomeration process for coal beneficiation. III. Grinding and agglomeration using different szego mill designs
Authors: McCracken Thomas W. , Trass Olev
Published: March 2009

The simultaneous grinding/agglormeration process has been used to beneficiate Minto coal. Experiments with the Szego Mill, a planetary ring‐roller mill with grooved rollers, have given good results. Different roller ridge/groove sizes have been tested and favourable oil‐coal‐water ratios established. Ash removal is closely related to grinding performance. Very short mill residence times, of the order of 10 seconds, are sufficient for microagglomerate formation. Considerable equipment and operating cost savings are possible with the modified process.
Mixing in the transition flow regime with helical ribbon agitators
Authors: Cheng Jianya , Carreau Pierre J.
Published: March 2009

The effects of the non‐Newtonian properties on the effective deformation rate, mixing and circulation times and flow behaviour have been investigated in the transition flow regime of mixing systems. Based on the equivalent Couette flow, three models are proposed and are shown to predict similar and drastic increases of the effective deformation rate with the impeller rotational speed in the transition regime. The predictions are shown to fit very well data obtained for various non‐Newtonian fluids mixed with helical ribbon agitators, and with literature data for anchor, blade turbine and flat disc agitators. The elasticity along with shear‐thinning properties appear to have slight effects on the dimensionless mixing and circulation times in the transition regime, whereas their effects in the laminar regime are quite drastic, as reported by others.
A bifurcation study of convective heat transfer in a hele‐shaw cell
Authors: Ryland D. K. , Nandakumar K.
Published: March 2009

Steady‐state multiplicity characteristics of convective heat transfer within a Hele‐Shaw cell are investigated. The Navier‐Stokes equations and the energy equation are averaged across the narrow gap, d, of the cell. The resulting two‐dimensional, stationary equations depend on the following parameters: (i) the length to height aspect ratio γ, (ii) the tilt anle ϕ (iii) the Prandtl number Pr, (iv) an inertia parameter ξ = d2/ 12a2, and (v) the Grashof number. Gr = Qgβga5/kv2. Here a is the height of the cell and Q, is the heat generation rate per unit volume. The complete structure of symmetric and asymmetric stationary solutions are traced using recent algorithms from bifurcation theory. In the double limit of ξ → 0 and Gr → ∞ such that Ra = 4GrPrξ remains finite (where Ra is the Rayleigh number for the Darcy model) the Hele‐Shaw model reduces to that of the Darcy model.
Modelling the influence of osmotic pressure gradients, interstitial volume, and lymphatic action on mass exchange in body tissues
Authors: Taylor D. G.
Published: March 2009

A mathematical model was employed to study the relative influences of interstitial osmotic pressure gradients, interstitial volume, lymphatic action and system geometry on the transcapillary exchange of fluid and plasma proteins within a modified Krogh cylinder tissue unit. The model includes a description of lymphatic behaviour and incorporates modified versions of the fluid and membrane transport equations to describe interstitial fluid flow under the influence of protein osmotic pressure gradients. The subsequent analysis suggests that these gradients have little effect on the overall hydrodynamics within the tissue. However, the properties of the draining lymphatic vessel and the radial dimension of the tissue cylinder exert strong influences on the magnitude and distribution of fluid and plasma protein fluxes across the capillary wall. The results of these simulations challenge current assumptions about transcapillary fluid flux distributions since they predict little exchange near the arteriolar end of the system in many cases. Further, as the radial dimension of the cylinder increases, the capillary moves from a state of fluid filtration along its entire length to one in which reabsorption occurs near the venular end of the blood vessel.
Biodegradation of 2,4‐dichlorophenoxy acetic acid (2,4‐d) by pseudomonas cepacia: Stoichiometric study
Authors: Fradette Sylvie , Leduy Anh , Rho Denis , Samson Réjean
Published: March 2009

Pseudomonas cepacia biodegraded 2,4‐dichlorophenoxyacetic acid (2,4‐D) according to the following stoichiometric equation:

C8 H6 Cl2 O3 + c1 O2 + c2 NH3 → c3 CHx Nz Oy + c4 CO2 + c5 H2 O + c6 Cl− + c7 REIM

where CHx Nz Oy represents the bacterial cells and REIM is the residual extracellular intermediate metabolites. The stoichiometric coefficients c1 to c7 were determined from C, N, O, H and Cl balances together with the experimental data on the biodegradation of 14 C‐carboxy‐labeled‐2,4‐D and 14 C‐ring‐uniformly‐labeled‐2,4‐D. The stoichiometric equation obtained predicted satisfactorily the total oxygen consumption for and the total heat production from the biodegradation of 2,4‐D for a wide range of initial concentrations from 80 to 500 mg/L.
Efficiency of dualflow trays in distillation
Authors: Xu Z. P. , Afacan A. , Chuang K. T.
Published: March 2009

The mass transfer efficiencies of dualflow trays with open hole areas of 20, 28 and 37% were experimentally investigated under total reflux conditions in a 300‐mm diameter distillation column using methanol‐water and methanol‐isopropanol systems. The results indicate that the efficiency of a dualflow tray is a strong function of the open hole area, the vapor/liquid load, and liquid properties such as surface tension and density. A fundamental model was developed to predict tray efficiency. The prediction was found to agree with the measured data to within 15.3%.
Effects of surface tension on tray point efficiencies
Authors: Chen G. X. , Afacan A. , Chuang K. T.
Published: March 2009

Sieve tray efficiencies for the distillation of methanol/water, acetic acid/water and cyclohexane/n‐heptane mixtures were measured as a function of composition under fixed vapour and liquid rates in a 0.15 m diameter distillation column. Experimental results show that surface tension has a significant effect on tray efficiency and the number of transfer units. Further tests in a simulator column with air/water, air/methanol and air/(water + surfactant) systems having different surface tensions revealed that bubble sizes in froths are mainly determined by surface tension. The results also show that bubble break‐up and coalescence occurs in the froths.
Anode slime behaviour in a laboratory‐scale copper electrorefining process
Authors: Ling X. , Gu Z. H. , Fahidy T. Z.
Published: March 2009

Combining conventional electrochemical measurements, laser‐based visualization and digital image processing, the movement of anode slime, its spatial distribution and path of falling during the copper electrorefining process were investigated in a laboratory scale cell. Two types of anode slime, small agglomerates and fine particles were observed. The behaviour of the slime was found to be closely related to the electrolyte circulation pattern. Different circulation rates and direction can only change the magnitude of the falling rate of small agglomerates, but not its direction. The path of falling is essentially random. By contrast, the direction of circulation can change both the rate of movement and the direction in the case of fine‐particle slimes. Downward circulation accelerates the rate of settling; the higher the circulation rate, the faster the rate of slime removal from the cell
A diverse approach for the solution of the isothermal multiphase flash problem. Application to vapor‐liquid‐liquid systems
Authors: Stateva Roumiana P. , Tsvetkov Stefan G.
Published: March 2009

The paper presents a novel approach for the solution of the isothermal multiphase flash problem with particular application to systems exhibiting liquid‐liquid‐vapor equilibria. The approach includes a rigorous method for thermodynamic stability analysis as a first step and an efficient phase identification procedure. The stability analysis, exercised only once, uses a modification of the Gibbs tangent plane criterion. The identification procedure implements the results of the stability test in a sequence of liquid‐liquid and liquid‐vapor calculations only till the phase configuration with a minimum Gibbs energy is determined.

The efficiency and reliability of the proposed new method is illustrated by solving three typical problems encountered in enhanced oil recovery, natural gas processing and petrochemical industry.
In‐situ extraction and purification of ethanol using commercial oleic acid
Authors: Jassal D. S. , Zhang Z. , Hill G. A.
Published: March 2009

The flash process for the removal of ethanol from commercial oleic acid has been experimentally studied and modelled using a modified Redlich‐Kwong‐Soave equation of state (RKAES) and the ASPEN process simulator. Using feed ethanol and water concentrations spanning the range of expected liquid‐liquid extraction concentrations, it was found that 93.6% by weight of ethanol in the distillate was obtained consuming only 2 MJoules of energy per kilogram of ethanol recovered. The RKAES model was found to reasonably predict the ethanol recovery and purity with errors under 5%. Commercial oleic acid was found to be completely non‐inhibitory towards the growth of Saccharomyces cerevisiae cells when used for in‐situ extraction at a concentration of 50% of the total fermenter volume.
Separation of strong acids by electrodialysis with membranes selective to monovalent ions. An approach to modelling the process
Authors: Andrés L. J. , Riera F. A. , Alvarez R. , Audinos R.
Published: March 2009

In this work some mixtures of sulphuric and nitric acids have been separated and concentrated by selective electro‐dialysis (SED) using heterogeneous membranes. Selective membranes can now be used for the separation of acids since anion exchange membranes with reduced transport number to multivalent ions are commercially available. The electric performance of the system has been analyzed and a correlation between current density, hydrodynamic parameters and concentration was established. The modelling of the SED experiments can be achieved with a good fitting for various membrane configurations of industrial interest.

Experimental results show that at operation times lower than 40 minutes, the selective anion exchange membranes efficiently exclude the sulphate anions. The nitrate anions fall to zero concentration at 60 minutes of operation and then the sulphate anions begin to cross through the membrane.
Hydrogenation of (—)‐α‐pinene over nickel—phosphorus/aluminum oxide catalysts prepared by electroless deposition
Authors: Ko Sun‐Hua , Chou Tse‐Chuan
Published: March 2009

Liquid‐phase hydrogenation of (—)‐α‐pinene was investigated using a new type of amorphous nickel‐phosphorus catalyst supported on aluminum oxide. The catalyst was prepared by the electroless deposition of nickel on the solid support at atmospheric pressure and moderate temperature from an aqueous solution. Two types of supports, aluminum oxide powder and pellet, were used. Electron probe micro‐analysis (EPMA) indicated that the nickel profile on the aluminum oxide powder was uniform throughout the whole particle of the powdery support; however, the nickel deposition on the catalyst supported by pellet aluminum oxide exhibited an eggshell‐type profile with a thickness about 8 μm. The amorphous structure of the nickel was confirmed by X‐ray diffraction (XRD). The procedure by which the catalysts were prepared involved four steps: etching, sensitization, activation and deposition. The conditions employed for the sensitization, activation and deposition steps significantly affected the composition, structure, metal profile and activities of the catalysts. Etching, however, had a negligible effect on the properties of the catalysts. Very high selectivity was found for hydrogenation of (—)‐α‐pinene to cis‐pinane.
Performance of control strategies to track the trajectories of batch reactors
Authors: Chang Jyh‐Shyong , Huang Kuang‐Li
Published: March 2009

We propose a modified globally linearizing control (MGLC) structure and a nonlinear feedforward‐feedback control (NFF/FB) structure to track trajectories of processes in a batch reactor. The MGLC structure performs trajectory tracking perfectly when the model inversion can be obtained by linearization of state feedback. Otherwise, the NFF/FB structure is recommended. The performance of the control laws that we developed are compared with other control laws designed with the same technique. The proposed control law based on the MGLC structure exhibits robust performance whereas that based on NFF/FB structure produces decreased sensitivity to process noise.
Effect of feed cycling on plasmid stabilization during continuous fermentation: The case of variable plasmid loss probability
Authors: Patnaik P. R.
Published: March 2009

The effect of feed cycling on the stability of plasmid‐bearing cells during continuous fermentation has been analysed for the case where the probability of loss of the plasmid varies with time. The model consists of a system of delayed differential equations. By using a square‐wave profile of the dilution rate, a two‐fold increase in the concentration of plasmid‐bearing cells and the recombinant product can be achieved over what is possible with a constant dilution rate. The dilution rate has a stronger effect than the frequency. These results agree qualitatively with reported experiments. The plasmid loss probability and the differential growth rate show fluctuations for a square‐wave variation in the dilution rate, and even with a constant dilution rate they stabilise only after a length of time. These observations show that it is particularly important to account for variable plasmid loss probability in the initial phase of fermentation.
Transfert de chaleur dans un film tombant autour d'un cylindre horizontal
Authors: Agunaoun A. , Daïf A. , Grisenti M. , Barriol R.
Published: March 2009

Connaissant le débit initial d'un film mince de liquide tombant sur un ou plusieurs tubes horizontaux, on propose un modèle de calcul permettant la détermination des coefficients de transfert de chaleur locaux. Ce travail est effectué pour des nombres de Reynolds inférieurs à 2000 et pour un flux ou une température constant. Le modèle prend en compte non seulement les effets convectifs mais aussi la courbure de l'interface liquide‐vapeur. On évalue globalement la partie du film évaporée après son passage sur la surface d'échange. Les résultats de ce modèle montrent que dans le cas où le flux de chaleur pariétal est imposé, ce dernier n'a pas d'influence sur la valeur du coefficient d'échange. La prise en compte de la courbure de l'interface permet un meilleur accord avec l'expérience, en particulier en ce qui concerne l'évaluation du nombre de Nusselt moyen quand le nombre de Reynolds est supérieur à 1000.
Estérification de l'acide stéarique par des alcools légers: Catalyse homogène par les titanates
Authors: Nasr Elsayed , Guiraud Roland , Pellegatta Jean Louis , Blandy Claudine
Published: March 2009

L'estérification de l'acide stéarique par des alcools à bas points d'ébullition en présence de titanates, est réalisée dans un réacteur semi‐continu. L'étude cinétique de la réaction à haute température (condition où les titanates sont le plus efficaces), nécessite la prise en compte de la réaction non catalysée. L'intérět du catalyseur est précisé; la nature de l'espèce active qui dépend de réactions d'échanges très rapides est aussi discutée.
Optimum designs of longitudinal fins
Authors: Yeh Rong‐Hua
Published: March 2009

Employing fin parameter and tip temperature, a new concept with Lagrange's multiplier method is proposed to obtain the optimum width, height, heat dissipation, and efficiency of longitudinal fins for boiling heat transfer. A power‐law type heat transfer coefficient is assumed in this analysis. Longitudinal fins of rectangular, convex parabolic, triangular, and concave parabolic profiles are first investigated. It is found that the optimum dimensions of a fin depends upon fin profile area, heat transfer coefficient at the fin base, and the thermal conductivity of the fin. Then, the least material fin profile is derived for each single heat transfer mode. To facilitate the thermal design of heat transfer components, simple mathematical expressions for the optimum dimensions of fins are presented in this study.
Studies on the effects of various design and operational parameters on solid circulation rate in a recirculating fluidized bed
Authors: Alappat Babu J. , Rane V. C.
Published: March 2009

Effects of various operational parameters, such as draft tube superficial air velocity and solid inventory and design parameters such as jet diameter and clearance between perforated plate and draft tube bottom on the solid circulation rate of a recirculating fluidized bed are studied. A simple butterfly valve arrangement was used for the direct measurement of the solid circulation rate.
Bubble size and velocity measurement in gas—liquid systems: Application of fiber optic technique to pilot plant scale
Authors: Saberi S. , Shakourzadeh K. , Bastoul D. , Militzer J.
Published: March 2009

A new fiber optic probe was developed for the detection and measurement of bubble sizes and velocities in a gas‐liquid column. The probe is made of a single 1 mm plastic fiber with a sharp wedge tip. The calibration was carried out on a laboratory scale unit using a cine‐photographic technique to verify the measurements. Bubble velocities were calculated using two identical parallel fibers and the cross‐correlation technique. With the velocities and the passage time determined, it was then possible to determine the bubble diameter. Bubble diameters were within 10% of the measurements obtained with the cine‐photographic technique. After calibration, measurements were carried out on a pilot scale unit.
Mass transfer from highly soluble cylinders in cross flow: Some experimental results
Authors: Lohia P. K. , Narayan K. A. , Chhabra R. P.
Published: March 2009

Mass transfer coefficients from highly soluble cylinders in cross flow orientation have been determined experimentally. The separate contributions arising from the different parts of the cylinder, namely, the front, plane sides and the rear have been delineated by masking various parts of the test specimen. Simple empirical expressions are devised for the components as well as for the total mass transfer coefficient. The present results compare favourably with the literature data in the following ranges of conditions: 90 ≤ Rep ≤ 850; 600 ≤ Sc ≤ 1100 and 70 ≤ Sh < 210.
Critical impeller speed for solid suspension in multi‐impeller three phase agitated contactors
Authors: Dutta N. N. , Pangarkar V. G.
Published: March 2009

The critical impeller speed for solid suspension in gas‐liquid‐solid systems has been measured in multi‐impeller agitated contractors of 0.15 and 0.30 m and ID and 1.0 m height. Three types of impellers, i.e. disk turbine (DT), pitched turbine downflow (PTD) and pitched turbine upflow (PTU) were used. Air, deionised water and sand particles were used as the gas, liquid and solid phases, respectively. The superficial gas velocity and solid loading were varied in the ranges 0–15 mm/s and 0.5 to 10% w/w, respectively. The effects of impeller type and its diameter, particle size and loading and gas flow rate were studied. Some measurements of gas hold‐up and mixing time were also made in order to get some insight of the hydrodynamic behaviour of the reactor. The critical impeller speed for solid suspension in the presence of gas (nisg) was found to be more than that in the absence of the gas and the increase of critical speed correlated well with the gas flow rate. The influence of particle—liquid parameters on solid suspension speed in the gassed system was similar to but relatively weaker than that in the ungassed condition.
Tailoring Disorder and Dimensionality: Strategies for Improved Solid Oxide Fuel Cell Electrolytes
Authors: Garcia‐Barriocanal Javier , Rivera‐Calzada Alberto , Varela Maria , Sefrioui Zouhair , Díaz‐Guillén Mario R. , Moreno Karla J. , Díaz‐Guillén José A. , Iborra Enrique , Fuentes Antonio F. , Pennycook Stephen J. , Leon Carlos , Santamaria Jacobo
Published: March 2009

Towards cooler solid oxide fuel cells: Disorder and dimensionality (see picture) play an important role in determining ion mobility of bulk and artificially nanolayered materials and should be considered in the design of new electrolytes with enhanced conductivity.

magnified image

Reducing the operation temperature of solid oxide fuel cells is a major challenge towards their widespread use for power generation. This has triggered an intense materials research effort involving the search for novel electrolytes with higher ionic conductivity near room temperature. Two main directions are being currently followed: the use of doping strategies for the synthesis of new bulk materials and the implementation of nanotechnology routes for the fabrication of artificial nanostructures with improved properties. In this paper, we review our recent work on solid oxide fuel cell electrolyte materials in these two directions, with special emphasis on the importance of disorder and reduced dimensionality in determining ion conductivity. Substitution of Ti for Zr in the A2Zr2−yTiyO7 (A=Y, Dy, and Gd) series, directly related to yttria stabilized zirconia (a common fuel cell electrolyte), allows controlling ion mobility over wide ranges. In the second scenario we describe the strong enhancement of the conductivity occurring at the interfaces of superlattices made by alternating strontium titanate and yttria stabilized zirconia ultrathin films. We conclude that cooperative effects in oxygen dynamics play a primary role in determining ion mobility of bulk and artificially nanolayered materials and should be considered in the design of new electrolytes with enhanced conductivity.
Simulating the spatial distribution of clay layer occurrence depth in alluvial soils with a Markov chain geostatistical approach
Authors: Li Weidong , Zhang Chuanrong
Published: March 2009

The spatial distribution information of clay layer occurrence depth (CLOD), particularly the spatial distribution maps of occurrence of clay layers at depths less than a certain threshold, in alluvial soils is crucial to designing appropriate plans and measures for precision agriculture and environmental management in alluvial plains. Markov chain geostatistics (MCG), which was proposed recently for simulating categorical spatial variables, can objectively decrease spatial uncertainty and consequently increase prediction accuracy in simulated results by using nonlinear estimators and incorporating various interclass relationships. In this paper, a MCG method was suggested to simulate the CLOD in a meso‐scale alluvial soil area by encoding the continuous variable with several threshold values into binary variables (for single thresholds) or a multi‐class variable (for all thresholds being considered together). Related optimal prediction maps, realization maps, and occurrence probability maps for all of these indicator‐coded variables were generated. The simulated results displayed the spatial distribution characteristics of CLOD within different soil depths in the study area, which are not only helpful to understanding the spatial heterogeneity of clay layers in alluvial soils but also providing valuable quantitative information for precision agricultural management and environmental study. The study indicated that MCG could be a powerful method for simulating discretized continuous spatial variables. Copyright © 2009 John Wiley & Sons, Ltd.
An accurate gradient and Hessian reconstruction method for cell‐centered finite volume discretizations on general unstructured grids
Authors: Betchen Lee J. , Straatman Anthony G.
Published: March 2009

In this paper, a novel reconstruction of the gradient and Hessian tensors on an arbitrary unstructured grid, developed for implementation in a cell‐centered finite volume framework, is presented. The reconstruction, based on the application of Gauss' theorem, provides a fully second‐order accurate estimate of the gradient, along with a first‐order estimate of the Hessian tensor. The reconstruction is implemented through the construction of coefficient matrices for the gradient components and independent components of the Hessian tensor, resulting in a linear system for the gradient and Hessian fields, which may be solved to an arbitrary precision by employing one of the many methods available for the efficient inversion of large sparse matrices. Numerical experiments are conducted to demonstrate the accuracy, robustness, and computational efficiency of the reconstruction by comparison with other common methods. Copyright © 2009 John Wiley & Sons, Ltd.
Linear quadratic regulation for systems with time‐varying delay
Authors: Zhang Huanshui , Xie Lihua , Wang Wei
Published: March 2009

In this paper we study the linear quadratic regulation (LQR) problem for discrete‐time systems with time‐varying delay in the control input channel. We assume that the time‐varying delay is of a known upper bound, then the LQR problem is transformed into the optimal control problem for systems with multiple input channels, each of which has single constant delay. The optimal controller is derived by establishing a duality between the LQR and a smoothing estimation for an associated system with a multiple delayed measurement. Copyright © 2009 John Wiley & Sons, Ltd.
Discrete state observability of hybrid systems
Authors: Di Benedetto Maria D. , Di Gennaro Stefano , D'Innocenzo Alessandro
Published: March 2009

We propose a novel definition of observability, motivated by safety critical applications, given with respect to a subset ofcriticaldiscrete states that model unsafe or unallowed behaviors. For the class of discrete event systems, we address the problem in the setting of formal (regular) languages and propose a novel observability verification algorithm. For the class of switching systems, we characterize the minimal set of extra output information to be provided by the continuous signals in order to satisfy observability conditions, and propose a milder observability notion that allows a bounded delay in state observation. For the class of hidden Markov models, we analyze decidability and complexity of the verification problem. Copyright © 2009 John Wiley & Sons, Ltd.
Decentralized adaptive fuzzy sliding mode control for reconfigurable modular manipulators
Authors: Zhu Mingchao , Li Yuanchun
Published: March 2009

A stable decentralized adaptive fuzzy sliding mode control scheme is proposed for reconfigurable modular manipulators to satisfy the concept of modular software. For the development of the decentralized control, the dynamics of reconfigurable modular manipulators is represented as a set of interconnected subsystems. A first‐order Takagi–Sugeno fuzzy logic system is introduced to approximate the unknown dynamics of subsystem by using adaptive algorithm. The effect of interconnection term and fuzzy approximation error is removed by employing an adaptive sliding mode controller. All adaptive algorithms in the subsystem controller are derived from the sense of Lyapunov stability analysis, so that resulting closed‐loop system is stable and the trajectory tracking performance is guaranteed. The simulation results are presented to show the effectiveness of the proposed decentralized control scheme. Copyright © 2009 John Wiley & Sons, Ltd.
Gene Targeting in a HUES Line of Human Embryonic Stem Cells Via Electroporation
Authors: Ruby Katherine M. , Zheng Binhai
Published: March 2009

Genetic modification is critical for achieving the full potential of human embryonic stem (ES) cells as a tool for therapeutic development and for basic research. Targeted modifications in human ES cells have met with limited success because of the unique culture conditions for many human ES cell lines. The HUES lines of human ES cells were developed for ease of manipulation and are gaining increased utility in stem cell research. We tested conditions for gene targeting via electroporation in the HUES-9 human ES cell line and demonstrate here successful gene targeting at the gene encoding Fezf2 (also known as Fezl), a transcription factor involved in corticospinal neuron development. With a targeting strategy involving positive and negative selection that is applicable to all genes, we observed a gene targeting frequency of ∼1.5% for Fezf2, a gene not expressed in human ES cells. We found that conditions developed for gene targeting in mouse ES cells can be readily adapted to HUES cells with few key modifications. HUES-9 cells exhibit an intrinsically high efficiency of clonal expansion and sustain electroporation-based gene targeting procedures without any significant loss of pluripotency marker expression or karyotypic stability. Thus, human ES cell lines adapted for enzymatic passage and efficient clonal expansion can be highly amenable to genetic modifications, which will facilitate their application in basic science and clinical development.

Disclosure of potential conflicts of interest is found at the end of this article.
Bioluminescence Imaging of Olig2-Neural Stem Cells Reveals Improved Engraftment in a Demyelination Mouse Model
Authors: Sher Falak , van Dam Go , Boddeke Erik , Copray Sjef
Published: March 2009

A major issue in the potential application of neural stem cell (NSC)-based cell replacement therapy for demyelinating diseases is the question of the survival, functional behavior, and stability of implanted NSC-derived oligodendrocyte precursor cells (OPCs) over an extended period. To address this issue, we employed bioluminescence imaging (BLI) as a noninvasive longitudinal in vivo monitoring technique and followed the fate of NSCs isolated from luciferase–green fluorescent protein–actin transgenic mice after stereotactic implantation in the demyelinated corpus callosum of cuprizone-fed mice. We compared normal NSCs with NSCs that were primed to become OPCs by the induction of Olig2 overexpression (Olig2-NSCs). BLI, validated by immunohistochemistry, revealed that, after a steep cell loss after implantation during the first 3 weeks, approximately 10% of the Olig2-NSCs stably survived for 2 months after implantation, in contrast to <1% of the normal NSCs. Immunohistochemistry, at the light and electron microscopic levels, revealed that the majority of the surviving Olig2-NSCs had differentiated into an oligodendrocytic cell lineage and contributed to remyelination of axons in the corpus callosum. The number of axons remyelinated by the implanted cells, however, was a small fraction of the total number of axons remyelinated by endogenous oligodendrocytes. Apparently, most of the implanted NSCs did not survive the transition into an inappropriate non-neurogenic niche, compressed by surrounding host tissue, in hostile, inflammatory conditions created by activated microglia. Only the ones that managed to differentiate rapidly into a mature neural cell type and become functionally integrated survived.

Disclosure of potential conflicts of interest is found at the end of this article.
Tubulin heterodimers remain functional for one cell cycle after the inactivation of tubulin‐folding cofactor D in fission yeast cells
Authors: Fedyanina Olga S. , Book Adam J. , Grishchuk Ekaterina L.
Published: March 2009

Tubulin‐folding cofactor D plays a major role in the formation of functional tubulin heterodimers, the subunits of microtubules (MTs) that are essential for cell division. Previous work has suggested that, in Schizosaccharomyces pombe, cofactor D function is required during G1 or S phases of the cell cycle, and when it fails to function due to the temperature‐sensitive mutation alp1‐t1, cells are unable to segregate their chromosomes in the subsequent mitosis. Here we report that another mutation in the cofactor D gene, alp1‐1315, causes failures in either the first or second mitosis in cells synchronized in G1 or G2 phases, respectively. Other results, however, suggest that the kinetics of viability loss in these mutants does not depend on progression through the cell cycle. When cofactor D function is perturbed in cells blocked in G2, cytoplasmic MTs appear normal for 2–3 h but thereafter they disintegrate quickly, so that only a few short MTs remain. These residual MTs are, however, stably maintained, suggesting that they do not require active cofactor D function. The abrupt disassembly of MT cytoskeleton at restrictive temperature in non‐cycling cofactor D mutant cells strongly suggests that the life‐span of folded tubulin dimers might be downregulated. Indeed, this period is significantly shorter than the previously determined dissociation time of bovine tubulins in vitro. The death of mutant cells occurs inevitably after 2–3 h at restrictive temperature in the following mitosis, and is explained by the idea that MT structures formed in the absence of cofactor D cannot support normal cell division. Copyright © 2009 John Wiley & Sons, Ltd.
Early risk assessment for Alzheimer's disease
Authors: Carrillo Maria C. , Blackwell Andrew , Hampel Harald , Lindborg Johan , Sperling Reisa , Schenk Dale , Sevigny Jeffrey J. , Ferris Steven , Bennett David A. , Craft Suzanne , Hsu Timothy , Klunk William
Published: March 2009

The purpose of the Alzheimer's Association Research Roundtable meeting was to discuss the potential of finding diagnostic tools to determine the earliest risk factors for Alzheimer's disease (AD). Currently, drugs approved for AD address symptoms which are generally manifest after the disease is already well‐established, but there is a growing pipeline of drugs that may alter the underlying pathology and therefore slow or halt progression of the disease. As these drugs become available, it will become increasingly imperative that those at risk for AD be detected and possibly treated early, especially given recent indications that the disease process may start decades before the first clinical symptoms are recognized. Early detection must go hand‐in‐hand with qualified tools to determine the efficacy of drugs in people who may be asymptomatic or who have only very mild symptoms of the disease. Devising strategies and screening tools to identify and monitor those at risk in order to perform “prevention” trials is seen by many as a top public‐health priority, made all the more urgent by an impending growth in the elderly population worldwide.
Inferior meatus endoscopy and directed treatment for epiphora: Early experience with a novel approach
Authors: Rogers G. Aaron , Murchison Ann P. , Wojno Ted H. , DelGaudio John M.
Published: March 2009

Objectives

Epiphora results from obstruction along the nasolacrimal (NL) system. The inferior meatus (IM) is not routinely evaluated. IM pathology is common in patients with epiphora, allowing surgery to be directed at the IM.

Methods

Retrospective review of patients referred for epiphora. Patients underwent office endoscopy of the IM. Patients with identifiable pathology underwent intervention directed at the IM.

Results

Seventeen patients were evaluated, four with bilateral epiphora. Two had no IM disease, and one with pathology refused surgery. The remaining 14 (18 sides) had IM pathology. Two patients were successfully treated in the office. Twelve patients underwent surgery (16 sides). Three NLD orifices were obstructed by a cyst, and the remaining 13 by hypertrophied soft tissue at the level of the NLD orifice. Thirteen of 14 sides with distal NLD pathology had resolution or dramatic improvement and patent NL ducts with IM treatment alone. Obstruction extending proximal to Hasner's valve was found in four NL systems, and three developed recurrent epiphora. Median follow‐up was 9 months.

Conclusions

IM endoscopy identified pathology in most constant epiphora patients in this study. Pathology at the distal NL system portends a better outcome, whereas extension to the proximal NL duct had poorer outcome.
Gamma tubulin: A promising indicator of recurrence in squamous cell carcinoma of the larynx
Authors: Syed Mohammed Iqbal , Syed Sheeba , Minty Fay , Harrower Steven , Singh Jatinder , Chin Andy , McLellan Douglas R. , Parkinson Eric K. , Clark Louise J.
Published: March 2009

Objective

Centrosome amplification as detected by gamma tubulin (GT) immunostaining is associated with genetic instability and tumor aggressiveness. We assessed GT for its ability to predict recurrence of squamous cell carcinoma of the larynx (SCCL).

Study Design

Case series with chart review.

Materials and Methods

Five micron sections of 35 archival SCCL samples were subjected to antigen retrieval and immunostaining with antibody to GT. The keratin antibody CK5 served as a positive control for antigen retrieval, and tonsillar tissue was used as a negative control.

Results

Of the 35 tumors analyzed, 22 were associated with recurrence(R) and 13 were not (NR). Fourteen of the 22 R tumors, but 0 of 13 of the NR tumours had a GT staining score of 2+ or 3+ (P < 0.0002). GT was also related to recurrence in node‐negative tumors (P < 0.006) but was unrelated to T stage (P = 0.726).

Conclusions

GT staining appears to be a better predictor of tumor recurrence than T stage and also predicts recurrence in N0 tumors.
Host range and distribution of fruit-infesting pestiferous fruit flies (Diptera, Tephritidae) in selected areas of Central Tanzania
Authors: Mwatawala M.W. , De Meyer M. , Makundi R.H. , Maerere A.P.
Published: March 2009

The host range of major fruit fly pests in Central Tanzania was evaluated from October 2004 to October 2006. Samples of 48 potential hosts were collected and incubated for fruit fly emergence.Bactrocera invadenswas the dominant species in incidence expressed as the ratio of infested to total number samples collected, as well as infestation rate, expressed as number of flies emerging per unit weight. Eight new host fruits are reported. Infestation by native pests, such asCeratitis capitataandC. cosyra, was minor compared toB. invadens.Ceratitis rosawas the dominant species in temperate fruits, and Cucurbitaceae were mainly infested byBactrocera cucurbitae, a specialized cucurbit feeder. Among commercial fruits, high infestation incidences were observed in mango and guava, but they decreased throughout the fruiting season. Low infestation rates were observed in allCitrusspecies and in avocado, indicating these fruits as poor hosts for the studied fruit fly pests in this region. Widespread availability and abundance of fruit species studied here ensures year-round breeding ofB. invadens. Seasonal infestation differs, with mango being the most important host in October to January, while guava being important from February to August. Tropical almond showed very high incidence and infestation rate forB. invadensand might act as an important reservoir host, bridging the fruiting seasons of mango and guava. Soursop acts as an important host forC. cosyraafter the mango season.Ceratitis capitatais a pest of minor importance of the commercial fruits studied in this region.
Bioactivation of Selenocysteine Derivatiives by β-Lyases Present in Common Gastrointestinal Bacterial Species
Authors: Schwiertz Andreas , Deubel Stefanie , Birringer Marc
Published: March 2009

Studies in cell cultures and animal models have demonstrated cancer chemopreventive effects of certain selenium compounds. Here we describe the screening of cysteine S-conjugate β-lyase activity in bacterial species that are implicated in the bio-activation of sulfur- and selenocysteine derivatives. We screened a range of bacterial species commonly found in the human intestine for β-lyase activity on Se-p-methoxybenzylselenocysteine and the natural occurring S-methylcysteine and Se-methylselenocysteine conjugates. A high-performance liquid chromatography (HPLC)-assisted assay was established to determine specific acctivities of each strain. Of the 29 tested bacterial species, 22 showed specific activities towards the test compound reaching up to 10.1 U/mg protein, thereby accounting for 75% of total fecal activity (13.3. U/mg protein). Lysates of four bacterial strains (Bacteroides distasonis, bacteroides vulgatus, Enterococcus faecalis, and Enterococcus faecium), which exhibited high specific activities towards the test compound and which are known to be present at high numbers in the human intestine, were characterized further. Our results indicate that β-lyase activity is widely distributed in human intestinal bacteria and might play a key role in the bioactivation of selenocysteine derivatives.
Evaluation of Iron Status by Serum Ferritin Level in Iranian Carriers of Beta Thalassemia Minor
Authors: Hoorfar Hamid , Sadrarhami Shohreh , Keshteli Ammar Hassanzadeh , Ardestani Samaneh Khanpour , Ataei Manijeh , Moafi Alireza
Published: March 2009

Background: Conflicting data exists on iron metabolism in adults with beta thalassemia minor (BTM). The purpose of this study was to evaluate the serum ferritin (SF) levels in Iranian adults with BTM in order to determine the iron status in these subjects. Methods: Eighty four (41 males, 43 females) Iranian adults with BTM and 102 (55 males, 47 females) healthy subjects as a control group were enrolled in the study. SF level was measured by immunoradiometric assay (IRMA). Results: The mean SF concentration in the BTM group was 101.84 ± 8.5 μg/L, which was higher than the mean SF in non-BTM subjects (67.98 ± 5.4 μg/L, p = 0.001). Comparing SF concentrations between BTM males and males in the control group showed that the SF level was significantly higher in BTM males (150.57 ± 75.13 μg/L vs. 96.66 ± 56.79 μg/L, p < 0.001). Similar data was found for females (55.38 ± 47.94 μg/L in the BTM group vs. 34.42 ± 25.72 μg/L in the non-BTM group, p = 0.01). Conclusion: This study showed that BTM may play a role in improving iron status in females with BTM. However in males, BTM can lead to iron overload. Therefore, we suggest determining the levels of SF in subjects with BTM, especially in males, to avoid harmful effects of iron overload in early stages of the disorder.