MTFA as a measure for computer display screen image quality

Computer display screen image quality is known to vary widely. Attempts have been made the world over at defining objective scales to better assess image sharpness and clarity. The experiments reported here were stimulated by the recent US adoption of MTFA≥5 as a minimum quality criteria. A series of ten hard-copy photographs and seven retrievable display screens were developed for a monochrome, cathode ray tube terminal that differed only in objective image quality. This series of display screen images was presented to 22 office workers, who were asked to provide a subjective image quality judgement in the form of a numerical scale ranking. The subjects were instructed to match the display screen with photographs that they estimated to be most comparable in image quality. Finally, the subjects were asked to specify what they considered to be the minimum acceptable visual quality. It was found that the subjects could accurately rank low and minimum quality display images and that their subjective visual quality judgement corresponded well with the objective MTFA quality scale. The minimum acceptable display quality specified by the office worker group corresponded to MTFA≥7, which is substantially higher than the US criteria and would disquality 40% of the video display terminals currently marketed in Sweden.     

Characterisation of submicron particles produced during oxygen blown entrained flow gasification of biomass

In this paper submicron particles sampled after the quench during 200 kW, 2 bar(a) pressurised, oxygen blown gasification of three biomass fuels, pure stem wood of pine and spruce, bark from spruce and a bark mixture, have been characterised with respect to particle size distribution with a low pressure cascade impactor. The particles were also characterised for morphology and elemental composition by a combination of scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS) and high resolution transmission electron microscopy/energy dispersive spectroscopy/selected area electron diffraction pattern (HRTEM/EDS/SAED) techniques. The resulting particle concentration in the syngas after the quench varied between 46 and 289 mg/Nm³ consisting of both carbon and easily volatile ash forming element significantly depending on the fuel ash content. Several different types of particles could be identified from classic soot particles to pure metallic zinc particles depending on the individual particle relation of carbon and ash forming elements. The results also indicate that ash forming elements and especially zinc interacts in the soot formation process creating a particle with shape and microstructure significantly different from a classical soot particle.     

Quality of Service Schemes for IEEE 802.11 Wireless LANs – An Evaluation

This paper evaluates four mechanisms for providing service differentiation in IEEE 802.11 wireless LANs. The evaluated schemes are the Point Coordinator Function (PCF) of IEEE 802.11, the Enhanced Distributed Coordinator Function (EDCF) of the proposed IEEE 802.11e extension to IEEE 802.11, Distributed Fair Scheduling (DFS), and Blackburst. The evaluation was done using the ns-2 simulator. Furthermore, the impact of some parameter settings on performance has also been investigated. The metrics used in the evaluation are throughput, medium utilization, collision rate, average access delay, and delay distribution for a variable load of real time and background traffic. The simulations show that the best performance is achieved by Blackburst. PCF and EDCF are also able to provide pretty good service differentiation. DFS can give a relative differentiation and consequently avoids starvation of low priority traffic.     

Channeling knowledge: Expert Systems as communications media

Expert Systems (ES) are as yet imperfectly defined. Their two consistently cited characteristics are domain knowledge and expert-level performance. We propose that current structural definitions are inadequate and suggest a view of ES as communication channels. We proceed to explore the factors influencing applicability of ES technology to an enterprise and the impacts that could be expected. A consequence of this view is the idea of incremental information loss on the path from the expert to the ES user. Strategies for minimizing this loss derive naturally from our perspective and are evident in successful ES.     

Ergonomic procurement guidelines for visual display units as a tool for progressive change

The Swedish Telecommunications Administration (STA) has put to gether a set of requirement specifications for general purpose Visual Display Units (VDUs), and in particular for VDUs to be used in telephone directory services and similar computer supported customer services. For VDUs based on Cathode Ray Tube technology, a rationale is presented for ergonomic requirements such as dark characters on a light background, a minimum refresh rate of 70 Hz, limits for acceptable levels of electric and magnetic field strengths, and full tilt, swivel and height adjustability of the VDU. Standardized measurement methods for e.g. legibility and resolution are needed in further developing the ergonomic procure ment process.