Automated Feedback System Research Articles

Correlation between zone velocity and current in automated single capillary isotachophoresis-zone electrophoresis

In single capillary isotachophoresis-zone electrophoresis (ITP-CZE) the sample zone velocity is varying with its position in the capillary during the focusing step. When the voltage is kept constant, the current changes to the same extent. Correlation between the current and the sample zone velocity can therefore be used to calculate the velocity of the hydrodynamic flow that is needed to counterbalance the sample zone velocity. Measured data are in agreement with calculations implying that current monitoring can be used in an automated feedback system to regulate the hydrodynamic flow velocity during the focusing step. Conditions are described where automated anionic single capillary ITP-CZE can be performed without application of a hydrodynamic counterflow, extending its applicability to any commercially available CZE system. Correlation between the ITP current and the sample zone position in the capillary was used to determine the moment for automatic switching from ITP to CZE. The reproducibility of the corresponding CZE migration times is investigated in addition to the effect of the remaining ITP terminator zone length on the CZE separation. A remaining terminator zone length of 10% of the total capillary length still resulted in an acceptable CZE performance.

New developments in spectroellipsometry: the challenge of surfaces

Advances in technology, especially semiconductor technology, are providing new opportunities for the development and application of spectroellipsometry and related techniques, particularly for real-time diagnostics and control. Two recent examples of surface and near-surface analysis illustrate possibilities. Reflectance-difference spectroscopy of (001) GaAs growth surfaces under ultra-high vacuum and atmospheric-pressure conditions has provided the first evidence of dimer formation during organometallic chemical vapor deposition (OMCVD). Kinetic-ellipsometric determination of the composition x of Al x Ga 1− x As alloys during chemical beam epitaxy (CBE), with x established by a history-independent, minimal-data approach, has been used to realize the first fully automatic closed-loop feedback system for controlling growth directly. Possible future directions are discussed.

Automatic feedback system for resonant column testing : Morris, D V Geotech test JV13, N1, March 1990, P16–23

Automatic feedback system for resonant column testing : Morris, D V Geotech test JV13, N1, March 1990, P16–23

Calculation of trim settings for a helicopter rotor by an optimized automatic controller

An automatic feedback system, based on continuous monitoring of hub loads, is used to find the control settings that are required to obtain a given flight condition for a helicopter rotor. Optimum values of gains and time constants are determined, and the limitations of the controller are examined for flap-pitch dynamics. It is found that the present method shows good convergence and is superior to other trim techniques for systems with moderate damping or with many degrees of freedom. B c c C-L CL CM CM [CM] CT CT d