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Process Dynamics (process + dynamics)
Selected AbstractsEvaluating local hydrological modelling by temporal gravity observations and a gravimetric three-dimensional modelGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 1 2010M. Naujoks SUMMARY An approach for the evaluation of local hydrological modelling is presented: the deployment of temporal terrestrial gravity measurements and gravimetric 3-D modelling in addition to hydrological point observations. Of particular interest is to what extent such information can be used to improve the understanding of hydrological process dynamics and to evaluate hydrological models. Because temporal gravity data contain integral information about hydrological mass changes they can be considered as a valuable augmentation to traditional hydrological observations. On the other hand, hydrological effects need to be eliminated from high-quality gravity time-series because they interfere with small geodynamic signals. In areas with hilly topography and/or inhomogeneous subsoil, a simple reduction based on hydrological point measurements is usually not sufficient. For such situations, the underlying hydrological processes in the soil and the disaggregated bedrock need to be considered in their spatial and temporal dynamics to allow the development of a more sophisticated reduction. Regarding these issues interdisciplinary research has been carried out in the surroundings of the Geodynamic Observatory Moxa, Germany. At Moxa, hydrologically induced gravity variations of several 10 nm s,2 are observed by the stationarily operating superconducting gravimeter and by spatially distributed and repeated high-precision measurements with transportable relative instruments. In addition, hydrological parameters are monitored which serve as input for a local hydrological catchment model for the area of about 2 km2 around the observatory. From this model, spatial hydrological variations are gained in hourly time steps and included as density changes of the subsoil in a well-constrained gravimetric 3-D model to derive temporal modelled gravity variations. The gravity variations obtained from this combined modelling correspond very well to the observed hydrological gravity changes for both, short period and seasonal signals. From the modelling the amplitude of the impact on gravity of hydrological changes occurring in different distances to the gravimeter location can be inferred. Possible modifications on the local hydrological model are discussed to further improve the quality of the model. Furthermore, a successful reduction of local hydrological effects in the superconducting gravimeter data is developed. After this reduction global seasonal fluctuations are unmasked which are in correspondence to GRACE observations and to global hydrological models. [source] Simvastatin regulates oligodendroglial process dynamics and survivalGLIA, Issue 2 2007Veronique E. Miron Abstract Simvastatin, a lipophilic statin that crosses the blood-brain barrier, is being evaluated as a potential therapy for multiple sclerosis (MS) due to its anti-inflammatory properties. We assessed the effects of simvastatin on cultures of rat newborn and human fetal oligodendrocyte progenitor cells (OPCs) and human adult mature oligodendrocytes (OLGs) with respect to cellular events pertaining to myelin maintenance and repair. Short-term simvastatin treatment of OPCs (1 day) induced robust process extension, enhanced differentiation to a mature phenotype, and decreased spontaneous migration. These effects were reversed by isoprenoid products and mimicked with an inhibitor of Rho kinase (ROCK), the downstream effector of the isoprenylated protein RhoA GTPase. Prolonged treatment (2 days) caused process retraction that was rescued by cholesterol, and increased cell death (4 days) partially rescued by either cholesterol or isoprenoid co-treatment. In comparison, simvastatin treatment of human mature OLGs required a longer initial time course (2 days) to induce significant process outgrowth, mimicked by inhibiting ROCK. Prolonged treatment of mature OLGs was associated with process retraction (6 days) and increased cell death (8 days). Human-derived OPCs and mature OLGs demonstrated an increased sensitivity to simvastatin relative to the rodent cells, responding to nanomolar versus micromolar concentrations. Our findings indicate the importance of considering the short- and long-term effects of systemic immunomodulatory therapies on neural cells affected by the MS disease process. © 2006 Wiley-Liss, Inc. [source] Enhanced Photorefractivity of Poly(N -vinylcarbazole)-Based Composites through Electric-Field Treatments and Ionic Liquid DopingADVANCED FUNCTIONAL MATERIALS, Issue 3 2009José A. Quintana Abstract It is shown that the photorefractive (PR) performance of polymer composites based on poly(N -vinylcarbazole) can be improved when samples are subjected to an electric field for a certain time, i.e. conditioned, previous to the PR characterization. It is also found that for conditioned samples the addition of an organic ionic liquid to the PR composition allows to obtain PR effect without the need of using a sensitizer. The typical electric field treatment time at room temperature and at a field of 20,V µm,1 is 20,min. This procedure leads to a decrease of dark conductivity and an increase of photoconductivity, and consequently an increase of conductivity contrast. This results in higher PR two-beam-coupling gain coefficients and shorter response times, particularly at low fields. Dependencies of the process dynamics on impurities, applied field strength, temperature and the presence of an organic ionic liquid are examined in detail. It is remarkable the significant increase of the PR gain coefficients, and more drastically of the net gain coefficients, observed at low fields (<55,V µm,1), when an ionic organic liquid such as benzalkonium chloride is added to unsensitized conditioned PR composites. These findings open a new route to improve the PR performance, not only of PVK-based composites, but also of other types of organic materials, the main advantage being that no sensitizer is needed. [source] A stochastic formulation for the description of the crystal size distribution in antisolvent crystallization processesAICHE JOURNAL, Issue 8 2010M. Grosso Abstract A stochastic approach to describe the crystal size distribution dynamics in antisolvent based crystal growth processes is here introduced. Fluctuations in the process dynamics are taken into account by embedding a deterministic model into a Fokker-Planck equation, which describes the evolution in time of the particle size distribution. The deterministic model used in this application is based on the logistic model, which shows to be adequate to suit the dynamics characteristic of the growth process. Validations against experimental data are presented for the NaCl,water,ethanol antisolvent crystallization system in a bench-scale fed-batch crystallization unit. © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source] Control of a high-purity ethylene glycol reactive distillation column with insights of process dynamicsAICHE JOURNAL, Issue 8 2009Kejin Huang Abstract Inventory control is often regarded as less important than product quality control in the operation of reactive and nonreactive distillation columns (i.e., often detuned considerably in control system design). For the high-purity ethylene glycol reactive distillation column, the inventory control of top condenser is, however, an exception and plays actually a crucial role in the stable and effective process operation, reminding the necessity to thoroughly investigate the intricate dynamic mechanism and its complicated implications on control system synthesis and design. In this article, the dynamics of a high-purity ethylene glycol reactive distillation column is examined, and it is found that the complicated dynamics, for example, the nonminimum phase behavior and process nonlinearity, can be suppressed considerably with the tight inventory control of the top condenser. Moreover, an extremely low controllability is detected, implying the potential difficulties in process operation and thus the need of process design modification. In terms of these insights obtained, two control schemes are devised and studied. It is demonstrated that sharp improvement could be acquired in control system performance when the tight inventory control has been implemented in the top condenser. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] Synthesis of bulk MgB2 superconductors by pulsed electric currentAICHE JOURNAL, Issue 7 2006A. M. Locci Abstract A preparation method to simultaneously synthesize and consolidate bulk MgB2 superconductors from Mg and B commercial elemental powders by means of the spark plasma sintering technique is reported. The influence of process parameters on sintering process dynamics as well as product characteristics, determined by transport and magnetic measurements, is investigated. The superconducting properties of the obtained samples, and particularly the critical current density, are comparable or better than those corresponding to other MgB2 preparation techniques. Thus, the superconductive properties of the bulk MgB2 materials synthesized in this work are suitable for selected applications, such as magnetic levitation, magnetic screening, and fault current limiters. It should be finally noted that the proposed method represents a particularly rapid preparation route as compared to other techniques. © 2006 American Institute of Chemical Engineers AIChE J, 2006 [source] Three-bed PVSA process for high-purity O2 generation from ambient airAICHE JOURNAL, Issue 11 2005Jeong-Geun Jee Abstract A three-bed PVSA (pressure vacuum swing adsorption) process, combining equilibrium separation with kinetic separation, was developed to overcome the 94% O2 purity restriction inherent to air separation in the adsorption process. To produce 97+% and/or 99+% purity O2 directly from air, the PVSA process with two zeolite 10X beds and one CMS bed was executed at 33.44,45.60 to 253.31 kPa. In addition, the effluent gas from the CMS bed to be used for O2 purification was backfilled to the zeolite 10X bed to improve its purity, recovery, and productivity in bulk separation of the air. PVSA I, which made use of a single blowdown/backfill step, produced an O2 product with a purity of 95.4,97.4% and a recovery of 43.4,84.8%, whereas PVSA II, which used two consecutive blowdown/backfill steps, produced O2 with a purity of 98.2,99.2% and a recovery of 47.2,63.6%. Because the primary impurity in the O2 product was Ar, the amounts of N2 contained in the product were in the range of 4000,5000 ppm at PVSA I and several tens of ppm at PVSA II. A nonisothermal dynamic model incorporating mass, energy, and momentum balances was applied to predict the process dynamics. Using the linear driving force (LDF) model with constant diffusivity for the equilibrium separation bed and a modified LDF model with concentration dependency of the diffusion rate for the kinetic separation bed, the dynamic model was able to accurately predict the results of the experiment. © 2005 American Institute of Chemical Engineers AIChE J, 2005 [source] CHALLENGES IN MODELING HYDROLOGIC AND WATER QUALITY PROCESSES IN RIPARIAN ZONES,JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION, Issue 1 2006Shreeram Inamdar ABSTRACT: This paper presents key challenges in modeling water quality processes of riparian ecosystems: How can the spatial and temporal extent of water and solute mixing in the riparian zone be modeled? What level of model complexity is justified? How can processes at the riparian scale be quantified? How can the impact of riparian ecosystems be determined at the watershed scale? Flexible models need to be introduced that can simulate varying levels of hillslope-riparian mixing dictated by topography, upland and riparian depths, and moisture conditions. Model simulations need to account for storm event peak flow conditions when upland solute loadings may either bypass or overwhelm the riparian zone. Model complexity should be dictated by the level of detail in measured data. Model algorithms need to be developed using new macro-scale and meso-scale experiments that capture process dynamics at the hillslope or landscape scales. Monte Carlo simulations should be an integral part of model simulations and rigorous tests that go beyond simple time series, and point-output comparisons need to be introduced. The impact of riparian zones on watershed-scale water quality can be assessed by performing simulations for representative hillsloperiparian scenarios. [source] High-Pressure Polymerization of Ethylene in Tubular Reactors: A Rigorous Dynamic Model Able to Predict the Full Molecular Weight DistributionMACROMOLECULAR REACTION ENGINEERING, Issue 7 2009Mariano Asteasuain Abstract A rigorous dynamic model of the high-pressure polymerization of ethylene in tubular reactors is presented. The model is capable of predicting the full molecular weight distribution (MWD), average branching indexes, monomer conversion and average molecular weights as function of time and reactor length. The probability generating function method is applied to model the MWD. This technique allows easy and efficient calculation of the MWD, in spite of the complex mathematical description of the process. The reactor model is used to analyze the dynamic responses of MWD and other process variables under different transition policies, as well as to predict the effects of process perturbations. The influence of the material recycle on the process dynamics is also shown. [source] Kinetic Analysis and Optimization for the Catalytic Esterification Step of PPT PolymerizationMACROMOLECULAR THEORY AND SIMULATIONS, Issue 1 2005Saptarshi Majumdar Abstract Summary: A well-validated kinetic scheme has been studied for PPT, poly(propylene terephthalate) polymerization process in batch and semi-batch mode with tetrabutoxytitanium (TBOT), a proven catalyst. Optimization study and analysis for PPT are rare, as the industrial relevance of PPT just became vibrant due to the commercial availability of one of its monomers in industrial scale in the recent past. Correctness of the analysis is checked by a new approach and parameters for the model are estimated from available experimental data. Solubility of terephthalic acid (TPA) is less in reaction medium and this effect is also considered along with the reaction scheme. Several simulations have been performed to see various process dynamics and this ultimately helps in formulating optimization problems. Using recently developed and well tested real-coded non-dominated sorting genetic algorithm-II, a state-of-the art evolutionary optimization algorithm, a couple of three objective optimization problems have been solved and corresponding Pareto sets are presented. Results show remarkably promising aspects of productivity enhancement with an improvement in product quality. Sensitivity analysis for relatively uncertain solubility parameter is also performed to estimate its effect over the proposed optimal solutions. Multiobjective Pareto front for 3 objectives: degree of polymerization, time and (bTPA,+,bPG). [source] Online process mean estimation using L1 norm exponential smoothingNAVAL RESEARCH LOGISTICS: AN INTERNATIONAL JOURNAL, Issue 5 2009Wei Jiang Abstract A basic assumption in process mean estimation is that all process data are clean. However, many sensor system measurements are often corrupted with outliers. Outliers are observations that do not follow the statistical distribution of the bulk of the data and consequently may lead to erroneous results with respect to statistical analysis and process control. Robust estimators of the current process mean are crucial to outlier detection, data cleaning, process monitoring, and other process features. This article proposes an outlier-resistant mean estimator based on the L1 norm exponential smoothing (L1 -ES) method. The L1 -ES statistic is essentially model-free and demonstrably superior to existing estimators. It has the following advantages: (1) it captures process dynamics (e.g., autocorrelation), (2) it is resistant to outliers, and (3) it is easy to implement. © 2009 Wiley Periodicals, Inc. Naval Research Logistics 2009 [source] Cuscore Statistics to Monitor a Non-stationary SystemQUALITY AND RELIABILITY ENGINEERING INTERNATIONAL, Issue 3 2007Harriet Black Nembhard Abstract We investigate the monitoring of a process subject to minimum mean-squared error feedback control using cumulative score (Cuscore) charts. Specifically, we design Cuscore statistics to discover spike, step, bump, and ramp signals hidden in non-stationary disturbance for feedback-controlled processes. We develop the adjustment and monitoring policies for combinations of process dynamics, disturbance, and signal that are practical in industry. We also address issues of detection probabilities and distributions using simulation. A manufacturing case study is used to illustrate the utility of the Cuscore approach. Copyright © 2006 John Wiley & Sons, Ltd. [source] Local dynamic partial least squares approaches for the modelling of batch processesTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 5 2008N. M. Fletcher Abstract The application of multivariate statistical projection based techniques has been recognized as one approach to contributing to an increased understanding of process behaviour. The key methodologies have included multi-way principal component analysis (PCA), multi-way partial least squares (PLS) and batch observation level analysis. Batch processes typically exhibit nonlinear, time variant behaviour and these characteristics challenge the aforementioned techniques. To address these challenges, dynamic PLS has been proposed to capture the process dynamics. Likewise approaches to removing the process nonlinearities have included the removal of the mean trajectory and the application of nonlinear PLS. An alternative approach is described whereby the batch trajectories are sub-divided into operating regions with a linear/linear dynamic model being fitted to each region. These individual models are spliced together to provide an overall nonlinear global model. Such a structure provides the potential for an alternative approach to batch process performance monitoring. In the paper a number of techniques are considered for developing the local model, including multi-way PLS and dynamic multi-way PLS. Utilising the most promising set of results from a simulation study of a batch process, the local model comprising individual linear dynamic PLS models was benchmarked against global nonlinear dynamic PLS using data from an industrial batch fermentation process. In conclusion the results for the local operating region techniques were comparable to the global model in terms of the residual sum of squares but for the global model structure was evident in the residuals. Consequently, the local modelling approach is statistically more robust. L'application de techniques basées sur la projection statistique multivariée est reconnue comme étant une approche qui contribue à une meilleure compréhension du comportement des procédés. Les méthodologies clés incluent l'analyse des composantes principales (PCA) à plusieurs critères de classification, les moindres carrés partiels (PLS) à plusieurs critères de classification et l'analyse des niveaux d'observation discontinus. Les procédés discontinus présentent typiquement un comportement non linéaire et variable dans le temps et ces caractéristiques mettent au défi les techniques mentionnées ci-dessus. Devant ces défis, la méthode PLS dynamique est proposée pour saisir la dynamique des procédés. Des approches semblables pour supprimer la non linéarité des procédés incluent le retrait de la trajectoire principale et l'application des PLS non linéaires. On décrit une autre approche où les trajectoires discontinues sont subdivisées en régions opératoires avec un modèle dynamique linéaire/linéaire adapté à chaque région. Ces modèles individuels sont raccordés pour obtenir un modèle non linéaire global. Une telle structure présente un potentiel pour une approche différente du suivi des performances des procédés discontinus. Dans cet article, plusieurs techniques sont considérées pour la mise au point du modèle local, incluant les PLS à plusieurs critères de classification et les PLS à plusieurs critères de classification dynamique. En utilisant la série de résultats les plus prometteurs d'une étude de simulation d'un procédé discontinu, le modèle local comprenant les modèles de PLS dynamiques linéaires individuels a été comparé à la méthode de PLS non linéaires dynamique globale utilisant des données d'un procédé de fermentation discontinu industriel. En conclusion, les résultats pour les techniques des régions opératoires locales sont comparables au modèle global en termes de somme des carrés des résidus mais pour le modèle global, la présence d'une structure dans les résidus est évidente. En conséquence, l'approche de modélisation locale est statistiquement plus robuste. [source] Revisiting The Ziegler-Nichols Tuning Rules For Pi ControlASIAN JOURNAL OF CONTROL, Issue 4 2002T. Hägglund ABSTRACT This paper presents new tuning rules for PI control of processes with essentially monotone step response that are typically encountered in process control. The rules are based on characterization of process dynamics by three parameters that can be obtained from a step response experiment. The rules are obtained by maximizing integral gain subject to a constraint on the maximum sensitivity. They are almost as simple as the Ziegler Nichols tuning rules but they give substantially better performance. [source] Using ARX and NARX approaches for modeling and prediction of the process behavior: application to a reactor-exchangerASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 6 2008Yahya Chetouani Abstract Chemical industries are characterized often by nonlinear processes. Therefore, it is often difficult to obtain nonlinear models that accurately describe a plant in all regimes. The main contribution of this work is to establish a reliable model of a process behavior. The use of this model should reflect the normal behavior of the process and allow distinguishing it from an abnormal one. Consequently, the black-box identification based on the neural network (NN) approach by means of a nonlinear autoregressive with exogenous input (NARX) model has been chosen in this study. A comparison with an autoregressive with exogenous input (ARX) model based on the least squares criterion is carried out. This study also shows the choice and the performance of ARX and NARX models in the training and test phases. Statistical criteria are used for the validation of the experimental data of these approaches. The identified neural model is implemented by training a multilayer perceptron artificial neural network (MLP-ANN) with input,output experimental data. An analysis of the inputs number, hidden neurons and their influence on the behavior of the neural predictor is carried out. In order to illustrate the proposed ideas, a reactor-exchanger is used. Satisfactory agreement between identified and experimental data is found and results show that the neural model predicts the evolution of the process dynamics in a better way. Copyright © 2008 Curtin University of Technology and John Wiley & Sons, Ltd. [source] Fault detection and isolation for dynamic processes using recursive principal component analysis (PCA) based on filtering of signalsASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 6 2007Jyh-Cheng Jeng Abstract A systematic procedure for the fault detection and isolation of dynamic systems is presented. The inputs of the process first pass through the dynamic filters which represent the process dynamics. Then, principal component analysis (PCA) is applied to the data matrix consisting of these filtered signals and the process outputs for fault detection. In case of a fault being detected, owing to an artificial linear relationship existing in the data matrix, the last principal component (LPC) is adopted for fault isolation. A recursive algorithm for PCA based on rank-one matrix update of the covariance is derived to compute the LPC on line. Patterns of the LPC are devised to isolate these faults, which include constant-bias and high-frequency noises originating from sensor measurement, errors resulting from input disturbance and change in the process gain. Furthermore, the magnitude of the fault can also be identified from the computed LPC. An illustrative example is used to verify the effectiveness of the proposed method. Copyright © 2007 Curtin University of Technology and John Wiley & Sons, Ltd. [source] Experimentelle Bestimmung der hygrischen Sorptionsisotherme und des Feuchtetransportes unter instationären BedingungenBAUPHYSIK, Issue 2 2006Assistent und Laborleiter Rudolf Plagge Dr.-Ing. Mit der vorgestellten Augenblicksprofil-Methode (APM) werden sowohl die relative Luftfeuchte und die Temperatur, als auch der volumetrische Wassergehalt in bestimmten Positionen in einem porösen Material bestimmt. Die Messungen werden kontinuierlich unter instationären Bedingungen durchgeführt. Damit erlaubt die APM eine dynamische und gleichzeitige Messung der hygroskopischen Sorptionsisotherme und der hygrischen Feuchteleitfähigkeit für einzelne Kompartimente innerhalb der Materialprobe. Die Feuchteleitfähigkeit wird aus den sich zeitlich ändernden Potentialgradienten und den dazugehörigen Feuchteverteilungen für die jeweiligen Kompartimente berechnet. Die Anwendung nicht konstanter Randbedingungen in der APM erlaubt die Untersuchung des hygrodynamischen Verhaltes von porösen Materialien. In der vorliegenden Studie werden die zeit- und prozeßabhängige Feuchtespeicherung und der Feuchtetransport bestimmt. Die vorgestellten Adsorptions- und Desorptionsexperimente wurden an dem kapillar- aktiven Wärmedämmstoff Calciumsilikat durchgeführt. Die Ergebnisse geben das Hystereseverhalten und den Einfluß der Dynamik der Prozesse wider. In Positionen mit schnellen Feuchteänderungen wird die Feuchtespeicherfunktion im Vergleich mit Regionen langsamer Feuchteänderung nach oben verschoben. Die Feuchteleitfähigkeit als Funktion der relativen Luftfeuchte zeigt eine bedeutende Hysterese. Hingegen ist die Feuchteleitfähigkeit in Relation zum Wassergehalt nicht hysteretisch. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) Experimental determination of the hygroscopie sorption isotherm and the moisture conductvity under transient conditions. By means of the proposed Instantaneous Profile Method (IPM) the relative humidity or the capillary pressure as well as the volumetric water content at specific locations inside a porous medium can be determined. The measurements are carried out under transient conditions and continuously in time. Thus, the IPM allows dynamic measurements of the hygroscopic sorption isotherm and the hygroscopic moisture conductivity. In addition, the moisture conductivity can be obtained via calculation of the moisture flow distribution from the temporal change of moisture contents in the compartments of the sample. The application of non-constant boundary conditions in the IPM allows investigation of the hygrodynamic behaviour of porous materials. In the presented study, the time and process dependent moisture retention characteristic and moisture conductivity are determined. The adsorption and successive desorption experiments presented here have been performed on the capillary active insulation material Calcium Silicate. The results show a hysteretic behaviour with a pregnant influence of the process dynamics. At locations with a rapid moisture increase, the moisture retention characteristic is shifted up in comparison to regions with slow moisture change. The moisture conductivity as function of relative humidity shows a remarkable hysteresis. However, the moisture conductivity in relation to the water content turned out to be non-hysteretic. [source] | ||||||||||||||||