Dynamic modeling and parameter estimation for an ethlyene-propylene-diene polymerization process

New Page 1 A general dynamic model for continuous EPDM polymerization in which crosslinking and gel formation are attributable to reactions between pendant double bonds has been developed. A pseudo-kinetic rate constant method is introduced to construct a moment model for a pseudo-homopolymer that approximates the behavior of the actual terpolymer under long chain and quasi-steady state assumptions. The pseudo-homopolymer model is then used as the basis for application of the numerical fractionation method. The proposed dynamic model is capable of predicting polydispersities and molecular weight distributions near the gel point with as few as eleven generations, and in the post-gel region with as few as five. The overall molecular weight distribution (MWD) of the sol was constructed by assuming a Schulz two parameter distribution for each generation. A parameter selection procedure is proposed to determine the kinetic parameters that can be estimated from the limited plant data. The procedure is based on the steady-state parameter output sensitivity matrix. The overall effect of each parameter on the measured outputs is determined using Principal Component Analysis (PCA). The angles between the sensitivity vectors are used as a measure of collinearity between parameters. A simple algorithm which provides a tradeoff between overall parameter effect on key outputs and collinearity yields a ranking of parameters by ease of estimation, independent of the available data. Its nonlinear and dynamic extensions are also developed and tested to address the nonlinearity and dynamics of the parameters\u27 effects on the outputs. The key kinetic parameters determined by the parameter selection procedure were estimated from steady-state data extracted from dynamic plant data, using a newly developed steady state detection tool. A hierarchical extended Kalman filter (EKF) design is proposed to estimate unmeasured state variables and key kinetic parameters of the EPDM kinetic model. The estimator design is based on decomposing the dynamic model into two subsystems, by exploiting the triangular model structure and the different sampling frequencies of the on-line and laboratory measurements directly related to the state variables of each subsystem. Simulation tests show that the hierarchical EKF generates satisfactory predictions even in the presence of measurement noise and plant/model mismatch

Risk Factors for Radiographic Tibiofemoral Knee Osteoarthritis: The Wuchuan Osteoarthritis Study

Objective. To investigate the risk factors of radiographic tibiafemoral knee osteoarthritis (OA). Methods. A population-based cross-sectional survey was conducted in Wuchuan County. A questionnaire and bilateral weight-bearing posterior-anterior semi-flexed knee radiographs were completed and read for Kellgren and Lawrence (K/L) grade and joint space narrowing (JSN; 0–3 scale) in each compartment. An logistic regression analysis was performed for radiographic tibiafemoral, lateral compartment, and medial compartment knee OA, respectively. Adjusted odds ratios (OR) and 95% confidence intervals (CI) were calculated. Results. Age, sex, and knee injury were strongly associated with tibiafemoral, lateral and medial compartment knee OA. BMI also had a dose-response relationship with them. Physical activity level, and physical activity exposure at work, not significantly though, were associated with an elevated risk for this three kinds of knee OA. Conclusions. Physical activity exposure increased the risk of knee OA. It was likely to be the heavier physical activity in Wuchuan osteoarthritis study that counteracted the BMI gap compared with the Beijing and the Framingham OA study. We verified that Chinese had a more valgus alignment of the knee compared with Caucasian population, and this provide a possible explanation why Chinese have a higher prevalence of lateral compartment OA

The mechanism of atopic march may be the ‘social’ event of cells and molecules (Review)

The skin, the conjunctivae, the airways and the digestive tract compose a huge vulnerable biological surface, which is exposed to the external environment. An allergen can often trigger an allergic reaction at a number of sites or result in an atopic march. However, the mechanism of atopic march remains unclear. Less attention has been paid to the connection between the primary site and the atopic site, because current knowledge is established directly against harmful factors. Allergic hypersensitivity manifests in parts of the human body far away from the allergen. Growing evidence suggests that the epithelial cells serve as the 'engine' which initiates an allergic reaction through the production of large quantities of cytokines, chemokines and growth factors. Because the epithelial cells cover the entire surface of the skin, the conjunctivae, the airways, and the digestive tract, and are positioned at the terminals of neurons and the blood supply, the connection between the primary site and the atopic site can not be easily understood by the current knowledge of anatomy and of the neuroendocrine immune network. What is the linkage between these huge vulnerable biologic surfaces? This article highlights selected frontiers in allergy research of atopic march, and focuses on recently attained insights into the cellular and molecular events of primary and atopic lesions in the allergy progress. Special attention is paid to the homogeneity of the cellular and molecular events on the huge vulnerable surface. Based on currently available data we conclude that the skin, conjunctivae, airways and digestive tract may join together to form the frontier 'commonwealth union' in order to fight the allergen. The epithelial cells are the 'engine' as well as the main target which initiates both primary and atopic inflammatory reactions. The atopic lesion may 'duplicate' the primary contacted site of cellular and molecular events. The atopic march may be due to the intrinsic 'social' involvements of the positioned epithelial cells, but may not be totally controlled by the anatomic connection or the circulating systemic factors involved in allergy pathogenesis

Distribution and speciation of dissolved iron in Jiaozhou Bay (Yellow Sea, China)

The distribution of total dissolved iron (DFe) and its chemical speciation were studied in vertical profiles of the shallow and semi-closed Jiaozhou Bay (JZB, China) during two contrasting periods: summer (July 19th, 2011) and spring (May 10th, 2012). Samples collected from the surface, middle and bottom layers were analyzed by competitive ligand exchange-adsorptive cathodic stripping voltammetry (CLE-aCSV). The mean DFe concentration during the summer period (median 18.8 nM ; average 20.7 nM) was higher than in the spring period (median 12.4 nM ; average 16.9 nM), whereas the spatio-temporal variation in spring was larger than in summer. The DFe-values showed distinct regional and seasonal differences, ranging from 5.6 to 107 nM in spring period and 13.4 to 43.4 nM in summer period. In spring, the highest DFe-values were observed in the eastern coastal region, especially near an industrial area (up to 107 nM), whereas the DFe distribution in summer was relatively even. Due to a tide influence, the vertical variations in the DFe and Lt in both seasons were not significant. On average, the Lt concentration (one class of ligand was estimated in all samples), was higher in spring (35.2 ± 23.4 nM) than in summer (31.1 ± 10.3 nM). A statistically significant correlation was found between Lt and DFe concentrations, it was higher for the summer period than for the spring period. The conditional stability constants (logK′) of organic complexes with iron were weaker in spring (11.7 ± 0.3) than in summer (12.3 ± 0.3). The concentrations of Lt were higher in comparison to DFe in all samples: the average [Lt]/[DFe] ratio in the spring and summer samples was 2.4 and 1.5, respectively. Speciation calculations showed that the DFe in the JZB existed predominantly (over 99.99%) in the form of strong organic complexes in both seasons