Double loop electrochemical potentiokinetic reactivation test optimization in checking of duplex stainless steel intergranular corrosion susceptibility

The double loop electrochemical potentiokinetic reactivation (DL-EPR) test using an electrolyte of 33 pct H₂SO₄ solution with 0.3 pct HCl, at room temperature and at a potential scan rate dE/dt of about 2.5 mV/s, was chosen to evaluate the sensitization of austeno-ferritic duplex stainless steels (DSS). Reproducible and optimal test responses and high test selectivity in detecting integranular corrosion (IGC) susceptibility were verified for four DSS differing in their method of fabrication (cast or wrought) and their ferrite phase content (44 to 57 pct). The test was successfully used to analyze the interactions between precipitation, chromium depletion, and IGC sensitization of the UNS S31250 steel, which was aged between 6 minutes and 120 hours at temperatures varying from 500 °C to 900 °C. The eutectoid decomposition of the ferrite, at different aging temperatures, was investigated using various techniques. The chromium depletion was analyzed qualitatively by X-ray mapping in a scanning transmission electronic microscope (STEM) and quantitatively by analytical calculation based on the chromium diffusion in the ferrite. It was shown that the chromium content in the ferrite can decrease from 30 to 7.5 pct by weight during aging before total decomposition occurs. The interactions between precipitation and IGC sensitization during DSS aging were clearly shown by superimposing the time-temperature-start of precipitation (TTP) and time-temperature-sensitization (TTS) diagrams obtained from the DL-EPR tests performed for various levels of sensitization.     

Controllability and local accessibility - a normal form approach

Given a system with an uncontrollable linearization at the origin, we study the controllability of the system at equilibria around the origin. If the uncontrollable mode is nonzero, we prove that the system always has other equilibria around the origin. We also prove that these equilibria are linearly controllable provided a coefficient in the normal form is nonzero. Thus, the system is qualitatively changed from being linearly uncontrollable to linearly controllable when the equilibrium point is moved from the origin to a different one. This is called a bifurcation of controllability. As an application of the bifurcation, systems with a positive uncontrollable mode can be stabilized at a nearby equilibrium point. In the last part of this paper, simple sufficient conditions are proved for local accessibility of systems with an uncontrollable mode. Necessary conditions of controllability and local accessibility are also proved for systems with a convergent normal form.     

Use of Endostemon tereticaulis (Pear.) M.Ashby and Hyptis spicigera Lam. Plant Extracts as Corrosion Green Inhibitors for Mild Steel in 1M HCl: Electrochemical and Surface Morphological Studies

Protection of Metals and Physical Chemistry of Surfaces - In the present study, we evaluated the effect of corrosion inhibition of ethanol extracts from Endostemon tereticaulis and Hyptis spicigera...     

Nonlinearizable single-input control systems do not admit stationary symmetries

The main result of the paper states that almost any analytic single-input control system, which is truly nonlinear, that is not feedback linearizable, with controllable linearization at an equilibrium point, does not admit any symmetry preserving that point. By almost any system, we mean that we exclude a small class of odd systems, that admit just one nontrivial symmetry conjugated to minus identity. The obtained results are based on a recent classification of nonlinear single-input systems under formal feedback. We also describe symmetries of feedback linearizable systems.     

Strict feedforward control systems,linearisability, and convergent normal forms

This article discusses the feedback equivalence of multi-inputs feedforward control systems via smooth (resp. analytic) feedback transformations. We first address the state (resp. feedback) linearisation problem, and provide easily computable algorithms that yield explicit state (resp. feedback) linearising coordinates for systems in strict feedforward form. The application of the algorithms does not require checking the commutativity (resp. involutivity) of the distributions associated with the system, and the algorithms fail after few steps if the system is not linearisable. In the latter case, the algorithms are extended to provide coordinate systems bringing the system into a normal form which is a smooth (resp. analytic) counterpart of Kang's formal normal form. Illustrative examples for both the linearisation and convergent normal form include the vertical take off and landing aircraft, the multi-vehicle wireless testbed among others.     

Comparative evaluation of the antioxidant potential of some Iranian medicinal plants

Medicinal plants are a source for a wide variety of natural antioxidants. In the study reported here, we have conducted a comparative study between five medicinal plants having the same geographic origin: the Hamadan region in the west of Iran and growing in the same natural conditions. The amount of total phenolics and total flavonoids for parts of these plants used in Iranian popular medicine were evaluated. Furthermore, antioxidant activities for these parts using vitamin C equivalent antioxidant capacity (VCEAC) test were also evaluated. The results show that the antioxidant activities varied greatly among the different plant parts used in this study and some plants are rich in natural antioxidants especially leaves of Lavandula officinalis and of Melissa officinalis. A positive correlation between total phenolic or flavonoid contents and VCEAC was found with a correlation coefficient of R² = 0.961 and R² = 0.817, respectively. These findings show that phenolics in these plants provide substantial antioxidant activity.     

Real-time three-dimensional wind simulation for windmill rig tests

This paper deals with the methods of three-dimensional fixed-point wind speed real-time simulation modelled in large band, in order to use them in test rigs for experimental investigation of the wind energy conversion systems. The medium- and long-term components of the non-stationary wind speed are considered as known, being issued from measured data or by adopting a generic model. The spectral characteristics of three-dimensional turbulence are described either by the Kaimal or the von Karman models. The turbulence intensity and the length scale that take part in these models are calculated by the site parameters, using current standards. The basic idea of the methods for large-band three-dimensional wind simulation is to use rational shaping filters that approximate non-integer orders shaping filters issued from the Kaimal and the von Karman models. All the synthesized rational shaping filters use one time constant, automatically adapted to the medium- and long-term components that pilot the other time constants of the shaping filters by a set of parameters practically constant. Some numerical results concerning time series that simulate the non-stationary wind speed with three-dimensional turbulence components based on Kaimal and von Karman models are presented.