Determination Of Transfer Function Research Articles

Linear modeling of steady-state behavioral dynamics.

The observed steady-state behavioral dynamics supported by unsignaled periods of reinforcement within repeating 2,000-s trials were modeled with a linear transfer function. These experiments employed improved schedule forms and analytical methods to improve the precision of the measured transfer function, compared to previous work. The refinements include both the use of multiple reinforcement periods that improve spectral coverage and averaging of independently determined transfer functions. A linear analysis was then used to predict behavior observed for three different test schedules. The fidelity of these predictions was determined.

Incidence-angle selection and spatial reshaping of terahertz pulses in optical tunneling

We present spatially resolved measurements of the electric field of terahertz pulses undergoing optical tunneling that show strong pulse reshaping in both time and space. This reshaping is shown to be a result of frequency and incidence-angle filtering of the complex amplitude of the plane-wave basis set that makes up the pulse. This filtering leads to spreading of the pulse in the time and space dimensions, as expected from linear dispersion theory. Measurement of the pulse shape after transmission through an optical tunneling barrier permits direct determination of the complex system transfer function in two dimensions. The transfer function, measured over both thin and thick barrier limits, contains a complete description of the tunneling barrier system from which the phase and loss times can be directly determined.

The spatial resolution of near-field optical microscope on chromosomes and cell traces

The investigation of biological samples in molecular medicine and biology by near-field optical microscopy is subject to nonconstant experimental conditions, such as humidity and elasticity. Contrary to far-field microscopy, the obtainable spatial resolution in scanning near-field optical microscopy (SNOM) greatly depends on the specific experimental conditions. The experimental determination of the modulation transfer function (MTF), therefore, uses regular solid-state structures. This paper introduces a method for the approximate in situ determination of the MTF using, as an example, SNOM transmission measurements of metaphase humane chromosomes and cell traces. The method has its origins in the linear system transfer theory. In order to eliminate effects of nonconstant optical near-field conditions, the transfer function is determined from the properties of the light source and the measured intensity function at the edge of a chromosome or cell trace, which depends on the transmission of the probe.

High resolution and small volume automatic ultrasonic velocimeterfor liquids

A method is described to precisely measure the sound velocity ofliquids. The construction of a resonator cell for the simultaneous measurementof a sample liquid and a reference liquid is presented. The non-idealproperties of the cavity resonators are carefully considered for a superiorevaluation of the resonance frequency data. Also presented is a low-pricedelectronic set-up, designed for the computer-controlled determination of thecomplex transfer functions of the cavity resonators and also for automatictemperature monitoring and control. Possible sources of errors are discussedand some representative results are presented in order to illustrate therepeatability of the method and the accuracy of the sound velocity datarelative to a reference liquid.

Accurate transfer function determination for superconducting gravimeters

The transfer function for the cryogenic gravimeter GWR‐C021 operating at Membach (Belgium) has been experimentally determined by injecting known voltages into the control electronics of the system. The output of the gravimeter to the injected sine waves and step functions has been observed. This give a precise knowledge of the transfer function of the gravimeter. It allows one to reach a precision of better than 0.01 second in the phase response of the instrument, in agreement with the Global Geodynamics Project (GGP) requirements.

Hydrogen transport through α-iron studies using a current modulation method

A new transfer function for electrochemical hydrogen permeation through metallic membranes is defined, and its analytical expression is obtained through a theoretical model including surface processes and bulk diffusion. By means of the EIS technique combined with electrochemical hydrogen permeation, this transfer function was experimentally measured for iron membranes, covered with a thin layer of electrodeposited Pd at the exit side, immersed in alkaline media at the input cell. By fitting of the model to the experimental results a hydrogen diffusion coefficient in iron of 9.6 (±0.6) 10 −9 m 2 s −1 was obtained independently of the membrane thickness in agreement with the values obtained by other authors with different techniques. It has been demonstrated that the thin Pd layer avoids formation of an oxide film without introducing new significant delays. The determination of the permeation transfer function allows to obtain relevant information about the electrochemical mechanisms of hydrogen discharge on the metallic surface. © 1999 International Association for Hydrogen Energy.

Empirical transfer function determination by the use of multilayer perceptron

Neural Networks are relevant statistical methods to extract information from data when physical phenomena are very complicated and cannot be described in terms of theoretical analysis. Scatterometers are active microwave radar which accurately measure the power of the backscatter signal versus incident signal in order to calculate the normalized radar cross section ( σ 0) of the ocean surface. We use multilayer perceptrons in order to determine the Geophysical Model Function and to estimate the variability of the signal of ERS-1, ERS-2 and NSCAT scatterometers.

Optical characterization of probes for photon scanning tunnelling microscopy.

The photon scanning tunnelling microscope is a well-established member of the family of scanning near-field optical microscopes used for optical imaging at the subwavelength scale. The quality of the probes, typically pointed uncoated optical fibres, used is however, difficult to evaluate in a direct manner and has most often been inferred from the apparent quality of recorded optical images. Complicated near-field optical imaging characteristics, together with the possibility of topographically induced artefacts, however, has increased demands for a more reliable probe characterization technique. Here we present experimental results obtained for optical characterization of two different probes by imaging of a well-specified near-field intensity distribution at various spatial frequencies. In particular, we observe that a sharply pointed dielectric probe can be highly suitable for imaging when using p-polarized light for the illumination. We conclude that the proposed scheme can be used directly for probe characterization and, subsequently, for determination of an optical transfer function. which would allow one to deduce from an experimentally obtained image of a weakly scattering sample the field distribution existing near the sample surface in the absence of the probe.

Hydrogen diffusion in α-iron studied using an electrochemical permeation transfer function

A new transfer function for electrochemical hydrogen permeation through metallic membranes is defined, and its analytical expression is obtained through a theoretical model including surface processes and bulk diffusion. By means of the EIS technique combined with electrochemical hydrogen permeation, this transfer function was experimentally measured for iron membranes, covered with a thin layer of electrodeposited Pd at the exit side, immersed both in acid and alkaline media at the input cell. By fitting of the model to the experimental results a hydrogen diffusion coefficient in iron of 9.6 (±0.6) 10 −9 m 2 s −1 was obtained independently of both the membrane thickness and the input side solution pH in agreement with the values obtained by other authors with different techniques. It has been demonstrated that the oxide film formed on iron at the output side of the membrane delays hydrogen transport and that the thin Pd layer avoids the formation of this film without introducing new significant delays. The determination of the permeation transfer function allows to obtain relevant information about the electrochemical mechanisms of hydrogen discharge on the metallic surface.

Theoretical determination of the collimator geometrical transfer function for the reconstruction of SPECT data

Iterative SPECT reconstruction algorithms allow for the inclusion of information related to the geometric system response with accuracy and flexibility. Since the experimental setup of a camera-collimator system may vary considerably, it is necessary to fit the restoration potential of the algorithm to the actual acquisition conditions. In order to avoid any experimental procedure, the authors developed a method to calculate weighting factors from the theoretical knowledge of the geometric system response of a multihole collimator. The calculation of the weighting factors was based on an appropriate discretization of the Radon transform whose kernel was modified to describe the variable system response of the collimator.

Determination of the Rigorous Transfer Function of An Isothermal Titration Microcalorimeter with Peltier Compensation

An old problem in Isothermal Titration Calorimetry is the accurate characterisation of the instrument, i.e. the determination of the instrumental transfer function. Normally, this calibration is performed electrically or through well known chemical reactions, but the transfer function parameters obtained by both methods generally do not agree: the first method normally yields smaller time constants than the second one. This fact is explained by the different path the heat flux takes towards the thermal sink. However, the time constants must be independent of the experiment type (electrical or chemical). In order to attain this independency, a realistic physical model of the system is developed taking into account the different heat sources and the paths in the system and using physically attainable (experimental and theoretical) inputs for testing the model. Important results from the model study are that the instrument is represented by different transfer functions, depending on the heat source location, and that the time constants are the same, regardless of the heat source location. A very simple and fast method based on such non-phenomenological physical model for obtaining the transfer function of an Isothermal Titration Microcalorimeter is applied here.

Atmospheric propagation transfer function determination using an adaptive filter

In this Letter an alternative method for the experimental determination of the complex acoustic propagation transfer function is presented. The method uses an adaptive filter in system identification mode. The inputs to the system are the source and received signals. The transfer function is represented by finite impulse response filter coefficients. Good results were obtained using filter lengths in the range from 100 to 250 with a sampling rate of 12 k samples/s. The method is outlined and some representative results with experimental field data are given.

Identification of the Vertical Plane Motion Model of a High Speed Craft by Model Testing in Irregular Waves

Experiments in towing tanks are concerned with the determination of the motion transfer functions, which are obtained by testing in irregular waves. For this purpose a model of pitch and heave motions has been developed, and the identified models of the vertical plane motions of a high-speed craft are showed. Linear models are obtained for different sea states and ship speeds. A general low order model is obtained by pole-zero cancellation. So, a full model may be considered for simulation and verification, and a low order model for design. From the lowest order models, a state space model is obtained.

Determination of Seismograph System Transfer Functions By Inversion of Transient and Steady-State Calibration Responses

The methods and software tools for the identification of the low-frequency portion of seismograph system transfer functions from transient (Dirac or step-impulse) calibration responses and of the high-frequency portion from steady-state (sinusoidal) calibration data are described. The presented procedures allow fast in-site determination of the overall Laplace transfer function of the analog stages of arbitrary seismograph systems. The developed identification software, which may also be employed for determining transfer functions in PAZ (polesandzeros) format from steady-state calibration data given graphically or in the form of FAP (frequency-amplitude-phase) triplets, has been made publicly available on the INTERNET. The paper is expected to prove useful especially for seismologists faced with the problem of specifying reliable calibration headers for digital upgrades of standard-class analog seismographs, for non-standard feedback-controlled seismograph systems, or for seismometric channels comprising inverse or simulation filters.

Multivariable Impulse Response Estimation via Correlation Analysis and Its Application to Automated System Identification

This paper presents a correlation analysis approach for estimating impulse response coefficients of multivariable systems where inputs and/or measured disturbances are allowed to be correlated with each other. The resulting estimator forms a simple linear equation set for which a simple closed form solution can be obtained, and due to the nonparametric nature of the estimator, the problem of selecting proper model structures encountered in parametric methods is avoided. These characteristics make the estimator very appropriate as a preliminary estimation step to more detailed parametric methods. Two other applications of the correlation analysis estimator include non-zero transfer function determination in multivariable systems and online identification experiment monitoring. The effectiveness of the proposed methods is illustrated on industrial data.

Restoration of images degraded by extreme mechanical vibrations

A method of numerically calculating the optical transfer function appropriate to any type of image motion and vibration, including random, has been recently developed. This method has been verified experimentally with real vibrations, and the close agreement justifies implementation in image restoration from blur deriving from any type of image motion, including random displacement. Here, image restorations of actual physically degraded images are presented, based on a constrained least squares improvement of the original Wiener filter. Even for extreme vibrations where the blur extent is much larger than the blurred detail, restoration is quite complete. The key to restoration is the determination of the optical transfer function unique to the particular image motion and vibration causing the blur. Results are also presented for low vibration frequency motion of random blur extent, as well as for high vibration frequencies.

Reconstruction of finite input signals

We present a method for reconstructing finite input signals for measurement transducers. The method converges if there is information on the finiteness of the input signal. The choice of a unique solution is based on additional information. Similar results are obtained for determination of finite pulse transfer functions.

High‐order volterra series analysis using parallel computing

This paper addresses the determination of high-order Volterra transfer functions of non-linear multiport networks containing multidimensional non-linear elements. A new method is developed for utilizing parallel computing which is very efficient for approximately 10–20 processors. The utilization of each processor may be as high as 80%–95%. The developed program is very flexible as it is ANSI C++ compatible and may run on both single- and multiprocessor computers. Using about eight processors it is possible to analyse rather complicated non-linear circuits up to ninth order in a few hours. © 1997 by John Wiley & Sons, Ltd.

High-order volterra series analysis using parallel computing

This paper addresses the determination of high-order Volterra transfer functions of non-linear multiport networks containing multidimensional non-linear elements. A new method is developed for utilizing parallel computing which is very efficient for approximately 10–20 processors. The utilization of each processor may be as high as 80%–95%. The developed program is very flexible as it is ANSI C++ compatible and may run on both single- and multiprocessor computers. Using about eight processors it is possible to analyse rather complicated non-linear circuits up to ninth order in a few hours. © 1997 by John Wiley & Sons, Ltd.

Determination of Differential Mobility Analyzer Transfer Functions Using Identical Instruments in Series

The differential mobility analyzer (DMA) is an important tool for determining particle size distributions. The physical performance of a DMA is quantified by the concept of the transfer function. Therefore, knowledge of the transfer function is important to interpret the mobility distributions recorded by a DMA. During a calibration workshop in preparation for the Aerosol Characterization Experiment 1 (ACE1) field campaign, the transfer functions of five types of different mobility analyzers (Vienna-type DMA short, medium, and long, CIT radial, and TSI long; CIT = California Institute of Technology, Pasadena, CA; TST = TSI Inc., St. Paul, MN) were experimentally characterized by height, width, and area of their transfer functions. Different particles size ranges between 3 and 200 nm were investigated. The transfer function was determined by scanning a DMA across the mobility distribution produced by another, identical DMA. Subsequently, the data were processed by a deconvolution algorithm assuming a triangular shape for the transfer function. For all DMA types, the area of the transfer function decreased with particle size, especially for ultrafine particles (d_p < 20 nm). The gradient with which this area decreases with particle size, however, is different for each of the DMA types investigated. The calibration provides an improved description of the performance of each DMA, particularly in the ultrafine size range.