Model simplification of signal transduction pathway networks via a hybrid inference strategy

A full-scale mathematical model of cellular networks normally involves a large number of variables and parameters. How to effectively develop manageable and reliable models is crucial for effective computation, analysis and design of such systems. The aim of model simplification is to eliminate parts of a model that are unimportant for the properties of interest. In this work, a model reduction strategy via hybrid inference is proposed for signal pathway networks. It integrates multiple techniques including conservation analysis, local sensitivity analysis, principal component analysis and flux analysis to identify the reactions and variables that can be considered to be eliminated from the full-scale model. Using an I·B-NF-·B signalling pathway model as an example, simulation analysis demonstrates that the simplified model quantitatively predicts the dynamic behaviours of the network

High resolution X-ray and electron microscopy characterization of PZT thin films prepared by RF magnetron sputtering

Pb(Zr0.52TiO0.48)O-3 (PZT) thin films grown on Pt/TiO2/SiO2/Si(1 0 0) substrates in the thickness range of similar to 30-550 nm by radio frequency (RF) magnetron sputtering method under different sputtering pressures were studied in the present work. High resolution grazing incidence X-ray diffraction method for residual stress and electron microscopy, particularly cross sectional transmission electron microscopy (XTEM), were used to identify the crystalline phases, and structure of the thin films at the nano-scale. Microstructure of the ultrathin films in <50 nm thickness range, consists predominantly of para-electric, oxygen deficient pyrochlore phase of Pb2Ti2O6 structure co-existing with ferroelectric perovskite PZT phase in tetragonal form. In films with thickness around 500 nm, sputtering pressure shows a strong influence on the purity of PZT phase grown. High resolution X-ray diffraction method for wafer curvature measurement and Stoney's equation were used to evaluate the biaxial stress in the films. It is found that the ultrathin films are compressively stressed with high magnitude of the order of 2 GPa which gets reduced with increasing film thickness. In the thickness range of similar to 500 nm, at an optimum sputtering pressure of 4.5 Pa, the stress becomes tensile in nature with a small magnitude of 2.3 MPa. At this pressure, the film consists of almost pure perovskite phase and comparatively better electrical characteristics. X-ray reflectometry study indicates very low density of PZT films with an interlayer formed at the interface with Pt. XTEM study throws valuable insight into the nano-scale structure and reveals the presence of nano-porosity along the interface as well as within the film microstructure. This has been attributed to the observed interface roughness, reduced density, tensile residual stress as well as the poor ferroelectric properties encountered