Search results for "transfer function"
showing 10 items of 152 documents
INFLUENCE OF PARTICLE-SIZE DISTRIBUTION MEASUREMENT METHOD ON THE PREDICTION OF SOIL WATER RETENTION CURVE
2013
Application of the Arya and Paris (AP) model to estimate the soil water retention curve requires detailed particle-size distributions (PSD) that can be obtained by fitting a continuous model to traditional sieve-hydrometer (SH) data or using the laser diffraction (LD) method. The AP model was applied to 40 Sicilian soils for which PSD was measured by both SH and LD methods. The scale factor was set equal to 1.38 (procedure AP1) or estimated by a logistic model with parameters gathered from literature (procedure AP2). To simplify application of the AP model, a relationship for estimating a soil-specific value from clay content was developed (procedure OPT). For both SH and LD data, proce…
Control flow strategy in a receiver coil for nuclear magnetic resonance for imaging
2020
A mathematical discussion is introduced to describe the receiver coil characterizing a nuclear magnetic resonance for imaging, starting from a general shape of the conductor. A set of different inductance calculations have been introduced, varying the shape of the conductor. The inductance calculation led to a general expression of the magnetic field of a single coil characterized by a rectangular shape. A dynamic model of the receiver coil has been developed to represent the natural frequencies that characterize the operational bandwidth. A nonstationary control strategy is implemented to make a real time changing of the operational bandwidth. The frequency response of the coil generates …
Tolerance to rotation of toric monofocal and bifocal intraocular lenses. A theoretical study
2018
Abstract This manuscript aims to evaluate the tolerance to rotation of a toric monofocal and a toric bifocal intraocular lenses with different cylinder powers. Theoretical designs based on wavefront aberrations were created to simulate a toric monofocal and a toric bifocal intraocular lens. Cylinder power ranged from −1 D to −6 D, in steps of −1 D. Tolerance to rotation was estimated by the visual Strehl ratio based on the optical transfer function (VSOTF) metric. Tolerance to rotation for both monofocal and bifocal intraocular lenses decreased when the cylinder power increased. For the bifocal design studied, the tolerance to rotation was larger for the near focus than for the far, however…
Fractional Derivatives in Interval Analysis
2017
In this paper, interval fractional derivatives are presented. We consider uncertainty in both the order and the argument of the fractional operator. The approach proposed takes advantage of the property of Fourier and Laplace transforms with respect to the translation operator, in order to first define integral transform of interval functions. Subsequently, the main interval fractional integrals and derivatives, such as the Riemann–Liouville, Caputo, and Riesz, are defined based on their properties with respect to integral transforms. Moreover, uncertain-but-bounded linear fractional dynamical systems, relevant in modeling fractional viscoelasticity, excited by zero-mean stationary Gaussian…
Nonsymmetric Fourier transforming with an anamorphic system
1984
The idea of obtaining a nonsymmetric Fourier transform with crossed cylindrical lenses of different focal lengths is presented. The anamorphic rotation-variant system produces a scaled Fourier transform F(u,mv) of an object f(x,y), where m is a scaling constant. The system performs controlled angular magnification of an object spectrum. It is shown that the super resolution in one direction is gained by reducing the number of degrees of freedom of the optical message in the other. Experimental results are shown where the scaling constant m of up to 10 has been obtained.
Three-dimensional point spread function and generalized amplitude transfer function of near-field flat lenses.
2010
We derive a nonsingular, polarization-dependent, 3D impulse response that provides unambiguously the wave field scattered by a negative-refractive-index layered lens and distributed in its image volume. By means of a 3D Fourier transform, we introduce the generalized amplitude transfer function in order to gain a deep insight into the resolution power of the optical element. In the near-field regime, fine details containing some depth information may be transmitted through the lens. We show that metamaterials with moderate absorption are appropriate for subwavelength resolution keeping a limited degree of depth discrimination.
Identification and Robust Control of a Quadratic DC/DC Boost Converter by Hammerstein Model
2015
This paper deals with the theoretical framework definition and the experimental application of the Hammerstein (HM) identification and related robust control technique to a quadratic dc/dc single-switch boost (Q-boost) converter. A set of fourth-order transfer functions (TFs) has been identified with the Hammerstein approach, on the basis of a pseudorandom-binary-sequence (PRBS) excitation signal. The set of identified TFs has been then used to design a suitable robust control technique, able to properly deal with the converter parameter uncertainty and load variations. The proposed approach has been tested in numerical simulation and validated experimentally on a suitably developed test se…
The effect of simulated normal and amblyopic higher-order aberrations on visual performance.
2012
Purpose To study the effect of simulated amblyopic and normal higher-order aberrations on visual performance of normal eyes. Methods To assess visual function, an adaptive optics visual simulator was used to compensate volunteers' ocular aberrations and simulate the wavefront aberration patterns found in healthy and amblyopic eyes in 7 healthy individuals. Visual acuity for high (100%), medium (50%), and low (10%) contrast and contrast sensitivity at 10, 20, and 25 cycles per degree (cpd) were measured after simulation of both pattern aberrations. The modulation transfer function and the point spread function were computed based on the aberration data. All measures were taken for 3 and 5.5 …
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…
Application and evaluation of the SWAP model for simulating water and solute transport in a cracking clay soil
2005
In Sicily, the increasing scarcity of quality water is leading to irriga- from salinization (Crescimanno et al., 2004). tion with saline water in soils having a considerable susceptibility to In Sicily, the increasing scarcity of good quality water cracking. Irrigation systems involving high application rates are used coupled with intensive use of soil under semiarid to arid in these irrigated areas, and bypass flow during irrigation is thus climatic conditions, is leading to irrigation with saline prevalent. Adoption of management practices accounting for cracking water on soils having a high shrink-swell potential and is therefore necessary to prevent salinization and land degradation. su…