2,479 research outputs found
Humans perceive flicker artifacts at 500 Hz.
Humans perceive a stable average intensity image without flicker artifacts when a television or monitor updates at a sufficiently fast rate. This rate, known as the critical flicker fusion rate, has been studied for both spatially uniform lights, and spatio-temporal displays. These studies have included both stabilized and unstablized retinal images, and report the maximum observable rate as 50-90 Hz. A separate line of research has reported that fast eye movements known as saccades allow simple modulated LEDs to be observed at very high rates. Here we show that humans perceive visual flicker artifacts at rates over 500 Hz when a display includes high frequency spatial edges. This rate is many times higher than previously reported. As a result, modern display designs which use complex spatio-temporal coding need to update much faster than conventional TVs, which traditionally presented a simple sequence of natural images
Web-based vocational English: development, practice and problems
In response to the IT in education initiative by Hong Kong\u27s Vocational Training Council, a project on web-based vocational English course was carried out at the Language Centre of Hong Kong Institute of Vocational Education (Tsing Yi) in September 1999. This project aimed to find out how to enhance language learning through integrating web-based and classroom-based activities. A survey was administered to investigate students\u27 response to this type of learning experience. In this paper, the development of the web-based activities and the integration process would be described and the survey results would be discussed
Chiral microstructures (spirals) fabrication by holographic lithography
We present an optical interference model to create chiral microstructures
(spirals) and its realization in photoresist using holographic lithography. The
model is based on the interference of six equally-spaced circumpolar linear
polarized side beams and a circular polarized central beam. The pitch and
separation of the spirals can be varied by changing the angle between the side
beams and the central beam. The realization of the model is carried out using
the 325 nm line of a He-Cd laser and spirals of sub-micron size are fabricated
in photoresist.Comment: 6 page
The Evolution of Density Structure of Starless and Protostellar Cores
We present a near-infrared extinction study of nine dense cores at
evolutionary stages between starless to Class I. Our results show that the
density structure of all but one observed cores can be modeled with a single
power law rho \propto r^p between ~ 0.2R-R of the cores. The starless cores in
our sample show two different types of density structures, one follows p ~ -1.0
and the other follows p ~ -2.5, while the protostellar cores all have p ~ -2.5.
The similarity between the prestellar cores with p ~ -2.5 and protostellar
cores implies that those prestellar cores could be evolving towards the
protostellar stage. The slope of p ~ -2.5 is steeper than that of an singular
isothermal sphere, which may be interpreted with the evolutionary model of
cores with finite mass.Comment: 19 pages, 3 figures, accepted for publication in the Astrophysical
Journa
- …