Extremum-seeking with variable gain control for intensifying biogas production in anaerobic fermentation.

A state-dependent variable-gain control system is implemented to follow the characteristics of a laboratory-scale up-flow anaerobic fixed-bed reactor dynamically. The transition from one state to another is determined on an hourly basis, depending on difference between the setpoint of the reactor pH and its true value. Considerable improvement of the process stability--reduction of oscillation in both the reactor pH and biogas production rate during high-rate operation, has been achieved, although the control structure is simple and intuitive.     

Changing the hydrogen content of alloy steel in relation to the technology used to cool cast slabs

Results are reported from the production of two trial heats of alloy steel in which the cast slabs were cooled in a thermostatted chamber and in a dense stack. It is shown that cooling slabs in such a chamber makes it possible to reduce the hydrogen content of the steel 30% compared to slabs that are cooled while stacked.     

Precision winding of fiber optic filament. II. Winding control

For pt.I see ibid., vol.39, no.3, p.258-67 (1992). The winding of fiber optic filament in the hoop, or precision, pattern is considered. Various automatic control options that have been designed and tested are described. The controllers are designed to regulate the fiber lag angle, which is the angle at which the feed filament approaches the take-up spool. Successful, flawless winding is directly related to accurate lag regulation. The contributions are distinguished by the fact that the automatic winding rate is 10 to 30 times greater than that achieved before by operator-assisted winding     

Effects of measurement errors on microwave antenna holography

The effects of measurement errors appearing during the implementation of the microwave holographic technique are investigated in detail, and many representative results are presented based on computer simulations. The numerical results are tailored for cases applicable to the utilization of the holographic technique for the NASA's Deep Space Network antennas, although the methodology of analysis is applicable to any antenna. Many system measurement topics are presented and summarized     

Catching the wave [gravity wave communication]

In 1873, when James Clerk Maxwell published his treatise unifying electromagnetic theory, he stated that light was electromagnetic in nature and he predicted that electromagnetic waves of greater length might exist. A dozen years later, Heinrich Hertz constructed apparatus with which he generated and received these longer waves, and he demonstrated that their behavior was identical to that of light. In the century following Hertz, these longer waves, which we now call radio waves, have been utilized to provide a vast worldwide communication system. In his theory of general relativity, published in 1915, Albert Einstein postulated the existence of gravity waves that propagate at the speed of light. If these waves could be used for communication purposes, they would open a whole new spectrum for exploitation, independent of the electromagnetic spectrum. Why is it that today, three quarters of a century later, we don't have gravity-wave transmitting and receiving stations? The article examines the reasons for this and then determines quantitatively how far we are from adding gravity waves to our communications repertoire     

Vector-controlled induction motor drive with a self-commissioningscheme

Different vector-controlled structures are discussed, and their suitability for an economical and reliable industrial drive system is explored. From this, the design of a compact control hardware is derived, composed of an 80196 microcontroller and an ASIC (application-specific integrated circuit) for the generation of the pulsewidth modulation (PWM) signals. The drive system can be configured from a host computer or a hand-held servicing unit through a serial data link. Monitoring and diagnostic functions are included. A self-commissioning scheme permits the setting of the parameters for optimum dynamic performance of the induction motor. Various oscillograms demonstrate the behavior of the vector controller operating a 25-kVA PWM inverter     

Autonomous system expansion planning considering renewable energysources-a computer package

The authors describe the interactive package ASP (Autonomous System Planning), which determines the optimal expansion plan of an autonomous generation system including diesel units, wind generators, and photovoltaic generators. Utilizing meteorological data, load demand data and estimated economical parameters, the package finds the optimal system expansion policy for a period of N years. The solution algorithms implemented in the package recognize planning and operational constraints and take into consideration the stochastic nature of the meteorological conditions, loads, and the availability of the diesel units     

Methods to assess physical activity with special reference tomotion sensors and accelerometers

Motion sensors may be applied for the assessment of physical activity. This paper reviews the evolution of these instruments from the mechanical pedometer to the electronic accelerometer. We conclude that for accurate assessment of physical activity under free living conditions the recently introduced accelerometer looks most promising, although little information was available regarding the reliability of these instruments. Subsequently, reliability of an accelerometer with a three-directional sensor was examined. Intrainstrument variation in a bench test was less than 8% during four measurements over a week. Interinstrument variation during treadmill experiments while subjects wore two accelerometers at the same time was on average 22% and was not improved after adjustment for differences found in the bench test. Reproducibility in the treadmill experiment was approximately 76, 85, and 95% at 3, 5, and 7 km/h, respectively. Bench testing revealed that the sensitivity of a piezoelectric element is prone to shifts, probably due to mechanical, electromagnetic, and/or temperature shock, which may be encountered during outdoor application. However, the relevance of the bench test in this study may be questioned, as results did not correspond with the findings in subjects. This needs further investigation.