Search results for "Flicker"
showing 10 items of 51 documents
CHANGES OF ELECTRONIC NOISE INDUCED BY OSCILLATING FIELDS IN BULK GaAs SEMICONDUCTORS
2008
A Monte Carlo study of hot-electron intrinsic noise in a n-type GaAs bulk driven by one or two mixed cyclostationary electric fields is presented. The noise properties are investigated by computing the spectral density of velocity fluctuations. An analysis of the noise features as a function of the amplitudes and frequencies of two applied fields is presented. Numerical results show that it is possible to reduce the intrinsic noise. The best conditions to realize this effect are discussed.
Fourier analysis of the stimuli for pattern-induced flicker colors.
1992
Pattern-induced flicker colors (PIFCs) were observed and color matched in rotating discs from which higher-harmonic Fourier components in the square-wave temporal luminance functions of a conventional black-and-white Benham disc had been removed. Since both reddish-brown and blue PIFCs were visible with purely sinusoidal stimuli they cannot result from differences in temporal stimulus shape or pattern and do not provide evidence for a temporal coding theory of color. Green PIFCs differed in that they did require the presence of additional harmonics. In a second experiment the luminance means upon which the sinusoidal PIFC stimuli were imposed were varied. The results show that color is dete…
Stochastic resonance in a tunnel diode in the presence of white or coloured noise
1995
We study the signal-to-noise ratio, signal and noise output levels in a fast bistable electronic system: a tunnel diode. We observe stochastic resonance when the system is driven by a sum of a small periodic signal and noise. The phenomenon is investigated for values of the driving frequency as high as 10 kHz. This is the highest frequency value used in SR experiments until now. In the presence of «white noise», we observe a nonmonotonic behavior characterized by a sharp dip in the output noise level measured at 100Hz and 1 kHz. A similar behavior is predicated by recent theories. We also present preliminary experimental results of SR in the presence of an Ornstein-Uhlenbeck noise. For the …
Computer-Aided Simultaneous Determination of Noise and Gain Parameters of Microwave Transistors
1979
A new method for the determination of noise and gain parameters of microwave linear two-ports (transistors) is presented. The method allows the simultaneous determination of the two parameter sets through a proper computer-aided procedure which processes the experimental data obtained from a measuring system employing noise meters and generators only. Experimental verifications carried-out on a microwave low noise transistor in S-band are reported.
On the noise resistance of field-effect transistors at microwave frequencies
2001
This paper presents a survey on the topical aspects of the noise resistance in field-effect transistors (FET) at microwave frequencies. Such noise parameter represents the sensitivity of the device noise figure to the departure from the minimum noise condition and is therefore important in all low-noise applications. The performance of the noise resistance in FETs has been reviewed since the first noise modeling analysis of short-gate devices were presented in the early '70s. The authors also comment and compare their own results on this subject as obtained by extensive experimental activity in the field of noisy device characterization vs. frequency, bias and temperature conditions.
Red-green flicker resolution as a function of heterochromatic luminous modulation.
1993
Critical fusion frequencies have been evaluated in heterochromatic red-green flicker as a function of red-green luminous modulation defined by mL = (R-G)/(R+G)%, at five different mean luminance levels, two test sizes (2 degrees and 5 degrees) and square wave stimuli. The extreme values mL = +/- 100 correspond to ordinary light-dark flicker (red or green); mL = 0 corresponds to pure chromatic flicker, and any other values correspond to simultaneous luminous and chromatic flicker. To implement the stimuli we have developed a new stimuli generator (AVICO, colour vision analyser) using bicolour LEDs as the light source and electronic control of the luminances and frequencies. The results for a…
Erhöhte Schwellen für die Detektion von Phasenunterschieden in musterinduzierten Flimmerfarben bei Patienten mit Glaukom
1994
BACKGROUND: Pattern-induced flicker-colors are subjective colors produced by rotating disks with black-and-white arcs. Changing the direction of rotation results in a different color. Small variations in the temporal sequence (phase differences) of the black-and-white pattern cause the colors to vary and can be perceived as color differences. PATIENTS AND METHODS: We investigated the thresholds for such phase differences in healthy (n = 11) and in glaucomatous (n = 19) eyes. Acuity and color vision were tested and in patients static visual field perimetry (Octopus G1) was carried out. The disks used for producing the pattern-induced flicker-colors were viewed from a distance of 2 m and had …
Assessment of virtual instruments measurement uncertainty
2001
Abstract In this paper, two methods to evaluate the measurement uncertainty of a virtual instrument are presented: a numerical method simulating the physical process of the A/D conversion, and an approximated theoretical method applying the “uncertainty propagation law” of the “guide to the expression of uncertainty in measurement”. After a brief description of the features, the constitution and the working principle of the virtual instruments, the various uncertainty sources, are analyzed. With both methods, the combined standard uncertainty of the measurement result is obtained, starting from the standard uncertainty generated by each single source and without taking into account the para…
Sensitivity of a sensory process to short time delays: A study in pattern induced flicker colors (PIFCs)
1978
Pattern induced flicker colors (PIFCs) were generated by means of a modified version of Benham's top, the stimulus pattern of which could be varied continuously during stimulation by the human subjects. The sensitivity of the color sensation to small phase shifts between the periodic stimuli on neighboring retinal areas was recorded under several conditions of stimulus parameters. A mathematical model was developed to describe the influence of the stimulus parameters on the recorded sensory effect. Concerning the underlying neurophysiological processes, a hypothesis is advanced according to which the phase sensitive lateral interaction within the retina changes the spatial excitation distri…
Colour vision experimental studies in teaching of optometry
2005
Following aspects related to human colour vision are included in experimental lessons for optometry students of University of Latvia. Characteristics of coloured stimuli (emitting and reflective), determination their coordinates in different colour spaces. Objective characteristics of transmitting of colour stimuli through the optical system of eye together with various types of appliances (lenses, prisms, Fresnel prisms). Psychophysical determination of mono- and polychromatic stimuli perception taking into account physiology of eye, retinal colour photoreceptor topography and spectral sensitivity, spatial and temporal characteristics of retinal receptive fields. Ergonomics of visual perce…