Search results for "Transfer function"
showing 10 items of 152 documents
Base-isolated structure equipped with tuned liquid column damper: An experimental study
2019
Abstract In this study, a novel passive vibration control strategy is investigated experimentally, where a Tuned Liquid Column Damper protects a base-isolated structure. The Tuned Liquid Column Damper is attached to the base, in contrast to typical attachment points of passive energy dissipation devices in high-rise buildings at elevated levels. Experiments on a base-excited small-scale three-story shear frame are conducted in order to study effects of both control devices – base-isolation and Tuned Liquid Column Damper – on the structural model. The dynamic properties of the stand-alone shear frame and the base-isolation subsystem are derived using standard dynamic test methods based on di…
Analysis of the level-crossing rate and average duration of fades of WSSUS channels
2017
Studies of the level-crossing rate (LCR) and the average duration of fades (ADF) are so far only devoted to stochastic processes being a function of one independent variable, which is usually time or in some few cases frequency. In this paper, we study the LCR (ADF) of wide-sense stationary uncorrelated scattering (WSSUS) processes in the time-frequency domain. A closed-form solution will be derived for the so-called time-frequency LCR (ADF) of the absolute value of the time-variant transfer function (TVTF) of WSSUS processes. It is shown that the LCR (ADF) is circularly symmetric in the normalized time-frequency domain. The derived time-frequency LCR contains the time LCR and frequency LCR…
Modulation transfer function: Rigid versus foldable phakic intraocular lenses
2008
Purpose To study in a standard eye model the changes in modulation transfer function (MTF) of a monofocal intraocular lens (IOL) when a phakic IOL (pIOL) is placed in the anterior chamber, compare the MTFs of the rigid Artisan pIOL and foldable Artiflex pIOL, and evaluate the temporal evolution of the MTF of the foldable pIOL after the mechanical stress the pIOL undergoes when injected. Setting Fundacion Oftalmologica del Mediterraneo, Valencia, Spain. Methods The MTF values of the IOLs were calculated from the cross-line spread function recorded with the Opal Vector System. The measurements were taken using an eye model following the British and EN-ISO standards with 2.0 mm, 3.0 mm, 4.0 mm…
Laser Speckle Size And Temporal Transfer Function In Human Vision
1988
Using a blue laser stimulus we measured TMTF with speckle sizes of 19.1 µm, 3.3 µm and absence of speckle. Our results indicate, if we compare the TMTF curves obtained for different speckle sizes, a gain of modulation due fundamentally to the presence of the spec kle; in the low frequency region this gain of modulation can be explained in terms of inhibitory effects. On the other hand, we observe by using the diffusion-inhibition model, that the presence of speckle in the test-field produces a delay of 12 ms and a reduction of the height of the response, with respect to that obtained in the uniform test (with absence of speckle).
Transmitter waveform and receiver transfer function modelling in time domain induced polarization
2012
SUMMARY In the computation of the forward response for Time Domain Induced Polarization the incomplete description of the transmitter waveform causes dramatic errors in the estimation of the magnitude and time characteristic of the IP phenomenon. Both the duration of the current pulse and the sequence of pulses used for the stacking procedure have a strong effect in the magnitude and shape of the IP decays. Furthermore, it is important to model low-pass filters of the receiver system, in order to extract all the information contained in the acquired data. For these reasons, a new 1D forward and inversion algorithms have been developed using the full time decay of the IP response and the rec…
Differential operator formalism for axial optical vortex beam and the double-phase-ramp converter
2019
A systematic study of the properties of the output dark rays or singular skeleton for the Laguerre-Gaussian beam LG 01 passed through double-phase-ramp converter is presented. When the DOE is discontinuous at the origin, as is the case here, the transfer function is not analytical, so that a special theoretical approach is needed. The previously reported formalism of scattering modes, which permitted the analytical calculation of arbitrary multisingular Gaussian beams, requires analyticity everywhere. We present here an adaption of this formalism that overcomes this limitation. The procedure is based on the differential operator algebra used in the previous construction. We give an example …
Sampling expansions for three-dimensional light amplitude distribution in the vicinity of an axial image point: comment.
2003
Landgrave and Berriel-Valdos presented axial and radial sampling expansions for three-dimensional light amplitude distribution around the Gaussian focal point. [J. Opt. Soc. Am. A 14, 2962 (1997)]. The expansions were obtained under the assumption that the pupil function was rotationally symmetric. We present a new derivation of the axial expansion that does not make use of arbitrary formal assumptions used by Landgrave and Berriel-Valdos and eliminates some faults of the derivation given by Arsenault and Boivin, who published this expansion in 1967 [J. Appl. Phys. 38, 3988 (1967)]. We also discuss generalizations of the axial expansion to the case of pupils that exhibit no symmetry with re…
Interferometric Phase Retrieval in Optical Transient Detection
2021
A transient detection imaging system (TDI), also known as optical novelty filter, is an adaptive interferometric device that detects temporal changes in a scene while suppressing its static parts. Removal of background improves contrast and helps visualizing and measuring intensity and phase. Following the first TDI proposal by Cudney et al. [1] , most TDI systems are based on photorefractive two-wave mixing [2] . Previous works rely on conventional intensity measurements, where partial information about input signal phase changes are obtained by previous calibration using an input phase-output intensity transfer function of the particular system.
In vitro optical quality differences between multifocal apodized diffractive intraocular lenses.
2013
Purpose To compare the in vitro optical quality of multifocal apodized intraocular lenses (IOLs) at different focal points. Setting University of Valencia, Valencia, Spain. Design Experimental study. Methods The Acrysof Restor +3.0 diopter (D) multifocal IOL with 2 main foci (bifocal IOL) and the Finevision multifocal IOL with 3 main foci (trifocal IOL) were evaluated. The optical quality was quantified using the modulation transfer function (MTF) at 7 focal points and for 3.0 mm and 4.5 mm apertures. The through-focus MTF at 10 focal points of the IOLs was also recorded. Results For the 0.0 D and −2.5 D focal points, the bifocal IOL showed the highest MTF values for pupil sizes as well as …
Modulation transfer function of a toric intraocular lens: evaluation of the changes produced by rotation and tilt.
2011
PURPOSE: To evaluate the changes in optical quality when toric intraocular lenses (IOL) are rotated or tilted and to demonstrate that IOL rotation produces an increasing effect of aberrations. METHODS: Modulation transfer function (MTF) and average modulation were used to analyze the image quality of a toric IOL. The axis of the toric IOL was rotated 5°, 10°, 15°, 20°, 25°, and 30° in successive MTF measurements. The tilt values were 0° to 5°, in increments of 1°, plus a tilt of 15°. Pupil diameters of 3 and 5 mm were used. RESULTS: The MTF decay due to aberrations was more sensitive to rotation than tilt. The main decrement in the average modulation, of approximately 50% in both pupils, o…