Analysis Of Transfer Functions Research Articles

Um novo algoritmo para a modelagem dinâmica de manipuladores flexíveis

Controlar de forma ativa estruturas flexíveis permanece um problema ainda em aberto, tendo sido objeto de muitas pesquisas, principalmente a partir dos anos oitenta. Apesar de existirem muitos trabalhos dedicados à modelagem dinâmica de tais estruturas, a obtenção de um modelo dinâmico realista e preditivo é de fundamental importância para o desenvolvimento de controladores. No presente artigo propõe-se um novo algoritmo para determinar de forma bastante simples, as equações diferenciais da dinâmica de uma estrutura do tipo manipulador com um único elo flexível. Desenvolve-se ainda funções de transferência analíticas para este problema específico, as quais são importantes para a validação do modelo discreto proposto na forma de um algoritmo.

EXPERIMENTAL VERIFICATION OF STRUCTURAL-ACOUSTIC MODELLING AND DESIGN OPTIMIZATION

A number of papers have been published on the simulation of structural-acoustic design optimization. However, extensive work is required to verify these results in practical applications. Herein, a steel box of 1·0×1·1×1·5 m with an external beam structure welded on three surface plates was investigated. This investigation included experimental modal analysis and experimental measurements of certain noise transfer functions (sound pressure at points inside the box due to force excitation at beam structure). Using these experimental data, the finite element model of the structure was tuned to provide similar results. With a first structural mode at less than 20 Hz, the reliable frequency range was identified up to about 60 Hz. Obviously, the finite element model could not be further improved only by mesh refinement. The tuning process will be explained in detail since there was a number of changes that helped to improve the structure. Other changes did not improve the structure. Although this model of the box could be expected as a rather simple structure, it can be considered to be a complex structure for simulation purposes. A defined modification of the physical model verified the simulation model. In a final step, the optimal location of stiffening beam structures was predicted by simulation. Their effect on the noise transfer function was experimentally verified. This paper critically discusses modelling techniques that are applied for structural-acoustic simulation of sedan bodies.

Spectrum and time modulation in measurements of optical signals and transfer functions varying in time

A solution of the phase problem in optics is considered as applied to the analysis of time-dependent signals and transfer functions describing optical features of the object under study. In particular, we analyze signals and processes of extremely short duration. A simulataneous analysis of the structure of the initial optical signal and of the amplitude and phase action of the object on the signal is performed. The modulation-spectrum approach is used to obtain the required information on the time behavior of the amplitude and phase of the optical testing signal before and after its interaction with the object. The object's influence is characterized by an additional modulation of the radiation. In order to obaain the information, the intensity distribution of the spectra of the testing signal passed through the object, of the signal subjected to an additional spectrum modulation and then passed through the object, and of the corresponding signals additionally modulated in time is detected. The modulation should provide, to a certain degree, a visualization of the phase information. The intensity distributions obtained in this way make it possible to calculate the structure of the signal under study and that of the time-dependent function that describes the object influence on the radiation.

Analysis of time-dependent optical signals and transfer functions by making use of spectral modulation

A modulation — spectral method is used to consider the solution of the phase problem in optics, as applied to the analysis of time-dependent signals and of transfer or instrumental functions describing the optical characteristics of an object under study. In particular, the reported analysis applies to ultrashort signals and processes. A version of simultaneous analysis of the structure of an initial optical signal and the amplitude — phase effect of an object or a medium under study on this signal, which is characterised by additional modulation of radiation, is considered. To obtain the desired information, it is necessary to record the spectral intensity distributions for a signal directly transmitted through an object, a signal subjected to additional spectral modulation and transmitted through an object, and the aforementioned signals with additional time modulation imposed in a certain way. To some extent, modulation should provide visualisation of the phase information.

Evolution of Small‐Scale Cosmological Baryon Perturbations and Matter Transfer Functions

The evolution of small scale cosmological perturbations is carefully re-examined. Through the interaction with photons via electrons, baryon perturbations show interesting behavior in some physical scales. Characteristic features of the evolution of baryon density fluctuations are discussed. In CDM models, it is found a power-law growing phase of the small-scale baryon density fluctuations, which is characterized by the terminal velocity, after the diffusion (Silk) damping and before the decoupling epoch. Then, a transfer function for total matter density fluctuations is studied by taking into account those physical processes. An analytic transfer function is presented, which is applicable for the entire range up to a solar mass scale in the high$-z$ universe, and it is suitable also to the high baryon fraction models.

Analytic nonlinear model for harmonics analysis in CMOS inverters

An analytic nonlinear model is proposed for analyzing the frequency response of digital circuits. Applying a Volterra series expansion method, we have developed analytic nonlinear Fourier transfer functions for a CMOS inverter. Comparison between our calculations and a SPICE simulation, its application to study the effects of device models on circuit performance, and its expansion in complex digital modules are discussed.

Empirical Methods for Determining the Stability or Instability of Certain Transfer Functions

We present some empirical methods for determining whether a linear autonomous dynamical system which has a known analytic transfer function is stable or unstable. These methods are based on the Poisson Integral representation forH∞mappings. Approximations of these integrals are often easily implemented by standard numerical packages, such as MATLAB, and thus present practical procedures for determining whether a given transfer function does or does not belong toH∞.

Generalized pole sensitivity analysis due to parameter perturbation

Recent research on pole sensitivity due to polynomial coefficient perturbation has significantly improved the understanding and accuracy of estimating pole sensitivity. This brief presents an expression for the sensitivity analysis of rational transfer functions with repeated and localized poles, extending the existing expression for sensitivity due to simple pole. This analysis provides estimates for an important question relating to pole sensitivity: Given the polynomial coefficient accuracy and pole locations, what is the resulting pole displacement?.

Resolving Oceanic Shear and Velocity with the Multi-Scale Profiler

Abstract The Multi-Scale Profiler (MSP), a freely falling dropsonde, has been used over the past 12 years to measure oceanic shear variance. Complete resolution of oceanic shear spectra is achieved by combining the measurements of MSP’s acoustic current meter (ACM), electromagnetic current meter (ECM), and airfoil probes. The ACM detects flow relative to MSP, so the platform motion must be known to determine the water velocity. The vechicl's tilt oscillation is inferred from accelerometer data, and its gross (point mass) horizontal motion is simulated by modeling MSP's response to the relative flow. Forcing on its tail array causes MSP to react as a point mass to fluctuations with scales as small as 2-3 m. The model of Hayes et al. for the TOPS dropsonde was modified so that it reasonably parameterized the large MSP tail force. Relevant dynamics and data processing are discussed, and the point-mass model is presented along with the analytic transfer functions that are used to select parameter values, asse...

Symbolic pole/zero calculation using SANTAFE

The aim of symbolic analysis is to gain insight into circuit behavior. To study the behavior of analog circuits, the locations of the poles and zeros have to be known. Unfortunately, no general method exists to calculate the poles and zeros symbolically for polynomials of degree greater than four from transfer functions in coefficient form. The CAD tool SANTAFE (Symbolic Analysis of Transfer Functions) applies the signal-flow graph method, which permits to keep the result in a factorized or partially factorized form. The graphic view provided by a signal-flow graph offers insight into the internal interactions between the circuit elements and, as will be demonstrated, enables the user to perform circuit knowledge-based approximations. A novel procedure based on symbolic Newton-iteration, accurately calculates high-order transfer functions in the desired pole/zero form. Another special routine, based on element weight ratios rather than numerical values, enables the simplification of large symbolic expressions without numerical values for each parameter. With the program SANTAFE, even large networks can be analyzed symbolically. This will be shown with an example of a wide band BiCMOS operational amplifier.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Harmonic generation in “non-linear” biological systems

We describe a high performance, low frequency Fourier Transform based spectrum analyser, with design features particularly suited to the harmonic analysis of the non-linear amplitude transfer functions of various biological systems. A previous published method, using general purpose systems to produce reference and signal plus reference “power” spectra, was susceptible to ambiguous interpretation of results. Unlike that design, the present spectrometer derives quantitative complex voltage (amplitude and phase) harmonics of sampled voltage data, maintaining potentially important information. Based on the use of a basic IBM or compatible PC, it features high sensitivity, high speed data processing and large dynamic range, is compact, easy to use, flexible in operation and low in cost. Its precision current signal source eliminates harmonics generated at the drive electrodes from the measurement. Use of the instrument leads us to conclude that, contrary to previous assertions, no repeatable dielectric or conductive non-linearity is exhibited in the bulk cell suspensions tested under the field and frequency conditions reported.

A New Theoretical Approach for the Prediction of Machine Tool Chatter in Milling

A new method for the prediction of chatter in milling is presented. The dynamics of the milling process are described by a set of differential-difference equations with time varying periodic coefficients. The stability of this system is examined using Fourier analysis and basic properties of the parametric transfer functions of linear periodic systems. The resulting characteristic equation is of infinite order and has constant coefficients. Its truncated version is used to determine the limit of stability employing standard techniques of control theory. The proposed method is applied to a theoretical example and a practical milling system.

Symbolic analysis of simplified transfer functions

This contribution presents new algorithms for the automatic simplified computation of symbolic transfer functions of linear circuits. The problem of symbolic simplification of transfer functions is defined and a set of algorithms able to cope with this problem and the simplified computation of poles and zeroes is developed and discussed. Results are reported with examples of circuits analyzed by our algorithms, showing good accuracy in their approximation, when compared to the corresponding SPICE simulations. Our technique merges the simplification procedure and the evaluation of the transfer functions, thus achieving significant improvements in terms of CPU time, compared with direct evaluation of the functions themselves.

Quantitative Analysis of Ostracoda and Water Masses around Japan: Application to Pliocene and Pleistocene Paleoceanography

Quantitative Analysis of Ostracoda and Water Masses around Japan: Application to Pliocene and Pleistocene Paleoceanography

Power modulation study of chemical kinetics in rf discharges

A method for measuring and modeling dominant kinetic rates and mechanisms in situ for an rf plasma has been developed. The coupling of small periodic power ] modulation(1)) of the discharge with transfer function analysis(2) provides a novel way to study the dominant reaction kinetics in the plasma environment. In this paper we review relaxation techniques used previously to study kinetics in the plasma and present a general description of relaxation methods. The theoretical analysis of transferfunctions for plasma power modulation is detailed with examples illustrating how information is assessed. The theoretical analysis is complemented by detailed descriptions of experimental transfer function development using phase-sensitive measurements. This explicit modeling of the transfer function requires knowledge of reaction rate coefficients, stoichiometry, and plasma conditions such as pressure, temperature, and residence time.

Observations on a principal components analysis of head-related transfer functions.

A recent principal components analysis (Kistler and Wightman, 1992) has shown that the transfer functions of the human external ear, for a wide range of source locations, can be expressed as weighted sums of a small number of basis vectors. Directional transfer functions obtained in this laboratory, using substantially different measurement techniques, yielded principal component basis vectors that are remarkably similar to those reported by Kistler and Wightman. When this subject population was divided in half according to the overall physical sizes of subjects, basis vectors computed for the subpopulation of smaller subjects were shifted systematically to higher frequencies relative to those computed for the subpopulation of larger subjects.

The barotropic electromagnetic and pressure experiment: 1. Barotropic current response to atmospheric forcing

During 1986–1987, an array of horizontal electrometers (which measure the subinertial barotropic velocity) was deployed for 11 months in the central North Pacific to study atmospherically forced motions in a low eddy kinetic energy region. Significant coherence is found to be ubiquitous between the barotropic velocity and one or more surface atmospheric variables over the North Pacific. The maximum squared coherence between currents and wind stress curl at all periods greater than 3 days is typically 0.6, rarely below 0.4, and occasionally above 0.8, and is dominantly nonlocal, although local coherence is seen at some sites, especially at the shorter periods. Both the coherence and the intersite pattern similarity are strongest at the periods of relative maxima in the barotropic current autospectra (e.g., at 6–8, 10–14, and 20–50 days). The locations at which the wind stress curl forces the motions at each site and for each period have been determined. While there is substantial intersite variability, some of the observed patterns of squared coherence over the North Pacific are very similar to those predicted by simple, linear, smooth‐bottomed, quasi‐geostrophic models of atmospherically forced barotropic currents. The forcing location is occasionally found to be the same spot for all oceanic instruments, especially at the autospectral maxima in barotropic current. More commonly, distinct forcing locations are found for each instrument even when closely spaced, suggesting topographic influence. In other cases, multiple forcing locations are implicated for the motions at a single station. All of this site‐ and period‐dependent variability of the forcing location is incompatible with the simple models and is due either to the known spatial inhomogeneity of the curl forcing field or to topographic effects. The importance of the former is emphasized using simple arguments based on analytic transfer functions between the atmospheric and oceanic variables and on observed wavenumber spectra for wind stress curl. Quantitative assessment of topographic effects must await suitable numerical models. In addition, maximum likelihood wavenumber spectra of the barotropic currents have been estimated in those bands with an adequate number of coherent sensors. The wavenumbers at the spectral peaks are compatible with the dispersion relation for Rossby waves modified by the observed, large‐scale, linearly sloping topography which shoals to the northeast. The observed group velocities are in general quite consistent with the inferred forcing locations based on the ocean‐atmosphere coherences.

Frequency limits for seismometers as determined from signal-to-noise ratios. Part 2. The feedback seismometer

AbstractThe range of frequencies that a seismometer can record is nominally set by the corner frequencies of its amplitude frequency response. In recording pre-event noise in very quiet seismic sites, the internally generated self-noise of the seismometer can put further limits on the range of frequencies that can be recorded. Some examples of such low seismic noise sites are Lajitas, Texas; Deep Springs, California; and Karkaralinsk, U.S.S.R. In such sites, the seismometer self-noise can be large enough to degrade the signal-to-noise ratio (SNR) of the recorded pre-event data. The widely used low seismic noise model (LNM) (due to Peterson, 1982; Peterson and Hutt, 1982; Peterson and Tilgner, 1985; Peterson and Hutt, 1989) is used as representative of the input ground motion acceleration power density spectrum (pds) at such very low noise sites.This study determines the range of frequencies for which the SNR of a feedback seismometer exceeds 3 db (a factor of 2 in power and 1.414 in amplitude). Analytic expressions for the SNR are developed for three types of feedback seismometers. These are the displacement feedback, velocity feedback, and coil-to-coil velocity feedback seismometers. It was found that the analytic SNRs of the displacement and velocity feedback seismometers are identical and that the SNRs for the coil-coil feedback seismometer and the electromagnetic seismometer are also the same.The signal pds using Peterson's LNM as an input is developed for each of the three types of feedback seismometers. Suspension noise is modeled following Aki and Richards (1980). In order to model the electronically caused component of the self-noise, the electronic noise properties of two commonly used operational amplifiers (Precision Monolithics OP-27 and the Burr-Brown OPA2111 FET) are described. Using these, noise models are developed for a synchronous demodulator and a chopper-stabilized amplifier. These noise models are used to numerically compute the SNRs for the two feedback seismometers used as examples, which are the Guralp Systems CMG-3ESP and Sprengnether Instruments SBX-1000 feedback seismometers. For each of the example seismometers, the calculated range of frequencies for which their SNR exceeds 3 db is as follows: the CMG-3ESP, 0.025 to 13.3 Hz; the SBX-1000, 0.098 to 11.3 Hz.The calculated and measured SNRs for the CMG-3ESP are compared. The calculated upper frequency for a SNR of 3 db was 13.3 Hz compared with 18.4 Hz measured in the noise tests. The calculated lower frequency for a SNR of 3 db was 0.025 Hz, whereas the measured value was 0.047 Hz. The difference is most likely due to the fact the CMG-3ESP is cut off at 0.1 Hz.Formulas are developed in Appendix A for calculating the SNR and self-noise of identical, colocated seismometers from their recorded outputs. The analytic transfer functions, midband gain, upper and lower corner frequencies, and bandwidths for the three types of feedback seismometers are given in Appendix B for comparison with the frequency limits set by the SNR.

Genetic analysis of transfer and incompatibility functions within the IncHI plasmid R27

This study was undertaken to establish a transfer complementation system for IncH plasmids and to locate regions of incompatibility within the HI1 plasmid, R27. Two regions of R27 were found to contribute to incompatibility as determined by incompatibility testing with fragments of R27 cloned in cosmid vectors. One of these regions hybridized with the IncHI1 rep probe (Couturier et al., Microbiol. Rev. 52, 375–395, 1988). Complementation analysis was carried out using transfer-deficient mutants of R27 in combination with pHH1508a. Cosmid vectors, which contained cloned restriction fragments of R27, were able to complement selected R27 Tra − mutants, enabling the transfer-deficient plasmid to transfer at near-normal frequencies. Complementation of R27 Tra − plasmids by pHH1508a at both 26 and 37 °C was shown to occur, but was host-dependent in its degree. These results suggest that the transfer mechanisms of IncHI and IncHII plasmids are related.

A Comparison of HDTV and Film — Overall Light Transfer Characteristics

This article discusses the ways in which the technical processes involved in HDTV and film imaging systems can be modeled with a succession of transfer functions that determine the overall visual characteristics of these systems. The overall transfer characteristic shows how the original scene is reproduced by a display. A theoretical analysis of the intermediate transfer functions provides insight into the reproduction of the scene. In addition, the viewing environment affects the choice of an overall, aesthetically pleasing transfer characteristic. Film, for example, is usually viewed in a dark room while television has traditionally been assumed to be viewed in brighter surroundings. Actual photometric measurements of both HDTV and film show that in a dark environment the two transfer characteristics are strikingly similar.