Pulsed processing by cold plasma, applied to industrial emission control.

A promising pollution control technology is cold plasma driven chemical processing. The plasma is a pulsed electric gas discharge inside a near atmospheric-pressure-temperature reactor. The system is energized by a continuous stream of very short high-voltage pulses. The exhaust gas to be treated flows through the reactor. The methods applied involve the development of robust cold plasma systems, industrial applications and measuring technologies. Tests of the systems were performed at many industrial sites and involved control of airborne VOC (volatile organic compound) and odor. Electrical, chemical and odor measuring data were collected with state-of-the-art methods. To explain the test data an approximate solution of global reaction kinetics of pulsed plasma chemistry was developed. It involves the Lambert function and, for convenience, a simple approximation of it. The latter shows that the amount of removal, in good approximation, is a function of a single variable. This variable is electric plasma power divided by gas flow divided by input concentration. In the results sections we show that in some cases up to 99% of volatile pollution can be removed at an acceptable energy requirement. In the final sections we look into future efficiency enhancements by implementation of (sub)nanosecond pulsed plasma and solid state high-voltage technology and by integration with catalyst technology.

Experimental setup for temporally and spatially resolved ICCD imaging of (sub)nanosecond streamer plasma.

Streamer discharges are efficient non-thermal plasmas for air purification and can be generated in wire-cylinder electrode structures (the plasma reactor). When (sub)nanosecond high-voltage pulses are used to generate the plasma, components like a plasma reactor behave as transmission lines, where transmission times and reflections become important. We want to visually study the influence of these transmission-line effects on the streamer development in the reactor. Therefore, we need a unique experimental setup, which allows us to image the streamers with nanosecond time resolution over the entire length of the plasma reactor. This paper describes the setup we developed for this purpose. The setup consists of a large frame in which a specially designed plasma reactor can be mounted and imaged from below by an intensified charge-coupled device (ICCD) camera. This camera is mounted on a platform which can be moved by a stepper motor. A computer automates all the experiments and controls the camera movement, camera settings, and the nanosecond high-voltage pulse source we use for the experiments. With the automated setup, we can make ICCD images of the entire plasma reactor at different instances of time with nanosecond resolution (with a jitter of less than several hundreds of picoseconds). Consequently, parameters such as the streamer length and width can be calculated automatically.

Auditory, visual and audiovisual perception of segmental speech features by severely hearing-impaired children.

Auditory alone, visual alone and audiovisual recognition of consonant-vowel consonant syllables were measured in 32 severely hearing-impaired children with hearing loss (PTA) in a narrow range around 90 dB HL when using their hearing aids. Multidimensional scaling analysis (INDSCAL) and information transmission analysis (ITA), applied to the confusion matrices obtained from the responses in each presentation mode and for each phoneme category, revealed perceptual dimensions and percentages of transmitted feature information (PTI). These were studied in relation to PTA, the auditory alone score and in relation to the efficiency of the audiovisual interaction (enhancement) over the probalistic summation of the auditory alone and visual alone score. INDSCAL analysis shows that auditory alone recognition of vowels is based on the perceptual dimensions F2 and F1 and that of consonants on the dimensions 'frication' and 'voicing'. In the auditory mode the interpretation of the INDSCAL dimensions in the stimulus spaces is in reasonable agreement with the ITA results. PTI decreases gradually with decreasing auditory alone phoneme score. Audiovisual recognition of vowels is based on a combination of the auditory dimension 'open/closed' (F1), and the visual dimensions 'lip rounding' and 'vertical lip opening'. Audiovisual recognition of initial consonants is based on a combination of the visual dimension 'front/back' and the auditory dimension 'continuance'. Recognition of final consonants is based on a combination of the visual dimension 'front/back' and an uninterpretable dimension. The perceptual dimensions are independent of both the level of the auditory alone phoneme score and audiovisual enhancement. Audiovisual enhancement is mainly a property of an individual and independent of both auditory alone and visual alone scores. ITA analysis, based on a phonological classification of the features, supports the results of the INDSCAL analysis in the auditory alone mode. It is not useful in the description of the audiovisual interaction, probably due to the phonological basis of the feature classification.