On-line monitoring of a CSTR polymerization reactor using multivariable filters

Three multivariable filters are evaluated for on-line monitoring of a CSTR polymerization reactor. The first filtering algorithm is the Kaiman filter. This linear filter is simple to implementation, but cannot exactly estimate the dynamic behavior of the polymerization reactor. To compensate the state model inadequacies, nonlinear models can be considered in the filtering algorithm. The precise state estimation can be guaranteed by the extended Kaiman filter (EKF). Finally, the auto-regressive exogenous inputs model based filter (ARXF) is developed to reduce the modeling cost. These different filters are applied to the continuous solution polymerization of a MMA-AIBN-EA system as a case study. The ARXF is easy to implement and shows satisfactory results.     

A conformational study of ethyl-substituted bithiophenes. Semi-empirical versus ab initio methods

Semi-empirical (AM1, PM3) and ab initio calculations (STO-3G, 3-21G¹) are employed to obtain the equilibrium optimized geometries and the torsional potential surfaces of 2,2′-bithiophene as well as its 3,4′- and 3,3′-ethyl-substituted derivatives. For the unsubstituted molecule, ab initio calculations have also been performed at the HF/6-31G¹ level. The geometries were completely optimized along the torsional potential curves to account for the molecular relaxation, yielding a physically meaningful picture of the nonrigid rotation. The results given by each theoretical method are compared and discussed. It is found that ethyl substitution causes rather small changes in the thiophene ring structure. Contrary to these results, ethylation dramatically influences the overall shape of the torsional potentials, leading to a large tilt from planarity. The barrier against planarity is found much higher for the 3,3′-ethyl derivative. It is also observed that the steric hindrance created by ethyl groups is much higher than that induced by methyl substituents.     

Dissection of P2X4 and P2X7 Receptor Current Components in BV-2 Microglia

Microglia cells represent the immune system of the central nervous system. They become activated by ATP released from damaged and inflamed tissue via purinergic receptors. Ionotropic purinergic P2X4 and P2X7 receptors have been shown to be involved in neurological inflammation and pain sensation. Whether the two receptors assemble exclusively as homotrimers or also as heterotrimers is still a matter of debate. We investigated the expression of P2X receptors in BV-2 microglia cells applying the whole-cell voltage-clamp technique. We dissected P2X4 and P2X7 receptor-mediated current components by using specific P2X4 and P2X7 receptor blockers and by their characteristic current kinetics. We found that P2X4 and P2X7 receptors are activated independently from each other, indicating that P2X4/P2X7 heteromers are not of functional significance in these cells. The pro-inflammatory mediators lipopolysaccharide and interferon γ, if applied in combination, upregulated P2X4, but not P2X7 receptor-dependent current components also arguing against phenotypically relevant heteromerization of P2X4 and P2X7 receptor subunits.     

Fabrication and oxidation behavior of Cr2AlC coating on Ti6242 alloy

An ∼ 5 µm Cr₂AlC coating was synthesized on near-α titanium alloy Ti6242 using an industrially sized magnetron sputtering coater. Isothermal oxidation at 700 °C and 800 °C, and cyclic oxidation at 700 °C of the bare alloys and coated specimens were investigated in air. The results indicated that the Ti6242 alloy faced serious oxidation problems at 700 °C and 800 °C. Repeated formation and spallation of the multilayered oxide scale on the Ti6242 alloy occurred during oxidation testing. The coated specimens exhibited much better oxidation behaviour as compared to the bare alloy. A continuous Al-rich oxide scale formed on the coating surface during the initial oxidation stages. The oxide scale and coating itself acted as diffusion barriers blocking the further ingress of oxygen and protected the substrate alloy from oxidation. The oxidation mechanisms of the bare alloy and the coated specimens were investigated based on the experimental results.     

Gravity induced solid grain packing during liquid phase sintering

The effects of gravity on the solid grain packing in liquid phase sintering have been investigated by both theoretical and experimental analyses. This treatment relies on quantitative microstructural measurements to determine the solid volume fraction variation along the direction of gravity. The model assumes that the grain packing coordination is proportional to the gravitational pressure and density difference between solid and liquid phases. It is confirmed by sintering experiments on W-Ni, and is consistent with a computer simulation model previously reported by German.     

Diffusion along [001] tilt boundaries in the Au/Ag system—II. atomistic modeling and interpretation

The low temperature boundary diffusion data obtained in Part I were modeledusing elementary vacancy, interstitialcy and interstitial defect mechanisms. First, boundary structures were calculated using the embedded atom method. Point defect formation energies at different boundary sites and migration energies betweenthem were then calculated, and values of δ_bD_b were determined using recently developed expressions for this quantity. The results indicate that the diffusion is dominated by a small number of jumps having relatively small activation energies and large partial correlation factors. Also, interstitial-related mechanisms make important (and perhaps dominant) contributions to the diffusion. Both the data and modelling indicate Arrhenius pre-exponential factors considerably smaller than those reported at high temperatures. It is suggested that additional jumps (possessing higher effective activation energies) exist, and that thei contributions become dominant at high temperatures. Finally, the observed δ_bD_b vs misorientation behavior is found to be quatitatively consistent with the structural unit model.     

Towards large area deposition of Cr2AlC on steel

Cr₂AlC belongs to the MAX phases, which are promising materials for protective coatings on steel due to their unique combination of properties like corrosion and oxidation resistance, good electrical conductivity, low friction coefficient, damage tolerance, and high temperature stability. Here the deposition of Cr₂AlC thin films has been carried out by magnetron sputtering of a Cr₂AlC compound target. The effect of the substrate temperature on the constitution was investigated. It was found that the MAX phase structure is stable in a substrate temperature range between 1123 K and 723 K. At lower substrate temperatures, the structure of the film is X-ray amorphous. A temperature of approximately 870 K was determined for the transition from amorphous to crystalline Cr₂AlC using differential scanning calorimetry. A phase purity of more than 90% MAX phase in the films was reached and the equilibrium volume is in excellent agreement with our ab initio calculations. The here presented deposition method provides a pathway towards large area deposition of MAX phase Cr₂AlC coatings on steel.