Input Power Spectrum Research Articles

Contribution of wall mechanics to the dynamic properties of aortic baroreceptors.

To examine the contribution of wall mechanics to dynamic properties of baroreceptors, we subdivided the transfer function of baroreceptors into two subsystems [aortic pressure to diameter and diameter to aortic depressor nerve activity (ANA)]. In six alpha-chloralose-anesthetized rabbits, we measured pressure, diameter, and ANA while randomly perturbing pressure. We obtained transfer functions (pressure to ANA, diameter to ANA, and pressure to diameter) by taking the ratio of crosspower spectrum to the input power spectrum (0.005-5 Hz). Below 3 Hz, the transfer function from pressure to ANA was nearly identical to that from diameter to ANA, whereas that from pressure to diameter was flat. Using transfer functions we could reproduce adaptation and hysteresis that were quantitatively similar between pressure-ANA transduction and diameter-ANA transduction. The pressure-diameter relationship was almost instantaneous and thus showed no hysteresis. In a second group of rabbits, the ratio of the shift of the hysteresis loop was unchanged by ouabain (40 micrograms/kg iv, n = 7). We conclude that the dynamic properties of baroreceptors may not be related to the wall mechanics or the Na(+)-K(+)-adenosinetriphosphatase activity.

Queue response to input correlation functions: continuous spectral analysis

Queueing performance in a richer, heterogeneous input environment is studied. A unique way to understand the effect of second- and higher-order input statistics on queues is offered, and new concepts of traffic measurement, network control, and resource allocation are developed for high-speed networks in the frequency domain. The technique applies to the analysis of queue response to the individual effects of input power spectrum, bispectrum, trispectrum, and input-rate steady-state distribution. The study provides clear evidence that of the four input statistics, the input power spectrum is most essential to queueing analysis. Furthermore, input power in the low-frequency band has a dominant impact on queueing performance, whereas high-frequency power to a large extent can be neglected. >

Queue response to input correlation functions: discrete spectral analysis

The authors explore a new concept of spectral characterization of wide-band input process in high speed networks. It helps them to localize wide-band sources in a subspace, especially in the low-frequency band, which has a dominant impact on queueing performance. They choose simple periodic-chains for the input rate process construction. Analogous to input functions in signal processing, they use elements of DC, sinusoidal, rectangular pulse, triangle pulse, and their superpositions, to represent various input correlation properties. The corresponding input power spectrum is defined in the discrete-frequency domain. In principle, a continuous spectral function of stationary random input process can be asymptotically approached by its discrete version as one sufficiently reduces the discrete-frequency intervals. An understanding of the queue response to the input spectrum will provide a great deal of knowledge to develop advanced network traffic measurement theory, and help to introduce effective network resource allocation policies. The new relation between queue length and input spectrum is a fruitful starting point for further research.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Joint transform correlator performance enhancement by a logarithmic- polar transformation

Rotation and scale requirements imposed by the joint Fourier transform correlator (JFTC) are relaxed by means of a logarithmic-polar transformation of the input object. The resulting target recognition/tracking system utilizes the positional invariance of the Fourier image, whereas the logarithmic-polar mapping is performed on the Fourier plane instead of the intensity of the Fourier plane. The positional information is saved, and consequently, multiple input objects are processed simultaneously. Enhancements in the areas of input binarization and power spectrum enhancements to the liquid crystal television based JFTC are performed to improve its recognition and discrimination abilities.

Stabilized Identification Via GSVD Optimized Based on Bayesian Information Theoretic Criterion and Minimum Mean Squares Error

Identification of an impulse response by using strongly correlated input signals is a typical ill-posed least squares estimation problem. In the present paper, multiple number of regularization parameters are employed to regularize the inversion of a rank-deficient matrix consisting of input signals. We give two approaches for determining these regularization parameters by using only accessible signal data. The first approach is based on minimization of a new Bayesian information theoretic criterion (ABIC) which can be derived on a basis of the Bayesian statistical approach. The second one is based on minimization of an estimated mean squares error (EMSE) of the parameter estimate. An iterative algorithm is given to calculate the optimal regularization parameters and the noise variance estimate simultaneously. By applying the proposed schemes, one can identify oscillatory peaks outside of the frequency range of the input power spectrum, even if the PE condition is not satisfied or even when the number of input-output data is rather less than the length of impulse response to be estimated.

Generalized Complex Damping and Spectral Integration

The spectral analysis and the corresponding integrations of the seismic‐response spectra of an offshore platform are presented. Any shape of the input power spectrum of the ground motion is described by piecewise straight lines for approximation. Both the effects of nonlinear drag force and modal‐damping coupling are taken into account in the analysis. The nonlinear drag force is linearized by the method of the least squares in the statistical sense, and the modal‐damping coupling is uncoupled by the use of the concept of generalized complex damping. As a consequence, the integration formulas of the response spectra for all vibrational modes have been derived, which may prove useful and efficient for computation.

Very sensitive measurement method of electron devices current noise

The problem of measuring very low levels of current noise in bipoles (linear or not) is dealt with, and a measurement technique is proposed. This technique allows the measurement of noise power spectra 6-10 dB lower than the equivalent input power spectrum of the amplified necessary to perform the measurement. An improvement of 16-20 dB in the sensitivity is obtained with respect to the one of conventional methods, which, for an acceptable accuracy, require the noise of the bipole under test to be 10 dB larger than the equivalent input one of the amplifier. The present method is based on the accurate measurement of the amplifier transimpedance with respect to the input current noise sources and on the precise evaluation and subtraction of the contribution from all the spurious sources to the total noise. The whole procedure is implemented by means of a dual-channel signal analyzer and almost completely automated. The technique has been tested by using it to measure the power spectra of the noise given by known generators, of the Nyquist noise produced by bipoles made up of resistors and capacitors, and of shot noise in p-n junctions. The experimental results agree very well with theoretical predictions. >

Calculation of third order intermodulation spectrum

A fast method for calculating the third order intermodulation spectrum by convolution of the input power spectrum using the FFT method is presented. The computation time is reduced to seconds even for large numbers of carriers. The computation time is insensitive to the number of different carrier types (level and bandwidth).

Non‐stationary structural response with evolutionary spectra using seismological input model

AbstractA recently developed seismological model of ground motion is incorporated into the non‐stationary random vibration theory making use of Priestley's evolutionary power spectral density. A general method of computing the input power spectrum is proposed and shown to reduce to the classical method when the input and the output are taken as stationary. Based on the concepts of Yang's non‐stationary envelopes and first‐passage reliability estimates via extreme point process, a statistical response spectrum for the pseudo‐velocity is developed. Comparisons made among the results of non‐stationary analysis with different modulating functions, and that of the stationary approximation, on SDOF linear structures with 5 per cent damping show that the type ofmodulating function chosen has little effect on the magnitudes of mean pseudo‐velocities, provided the input power spectrum is properly scaled, and that the stationary approximation produces conservative results for structures with natural periods greater than 0.5 sec.

Measurement of MTF by Noise Power Analysis of One-Dimensional White Noise Patterns

AbstractA method (or measuring the modulation transfer function (MTF) of digital printers is described that applies well-known techniques from the analysis of random data. More specifically, it is well-known that the input and output noise power spectra of linear systems can be used to estimate their transfer characteristics. In this application, small-amplitude one-dimensional white noise is used as the input to a digital laser printer. The noise power spectrum of the resulting film image is then estimated. From this the small-signal system MTF is obtained. This method will be demonstrated and discussed in the context of other methods described in the literature.

Phoneme information extracting apparatus

A phoneme information extracting apparatus includes correlation data generators for successively generating correlation data representing the correlation between the acoustic power spectrum data corresponding to input voice and power spectrum data of various reference phonemes, selection circuits for successively transferring these correlation data when they detect that three or more successive correlation data have values greater than a predetermined value, maximum data hold circuits for holding the maximum correlation data among the correlation data transferred from the respective selection circuits, and a phoneme determination circuit for determining the optimum phoneme by detecting one of the data hold circuits that is holding the maximum correlation data among the correlation data held in the data hold circuits.

The design and performance of a gimbal-type mounting for sprayer booms 2. Optimization model and validation

An empirical approach had already indicated that the gimbal-type mounting is effective in reducing movement of a sprayer boom. This mounting involves springs and viscous dampers and it was concluded that the effects of these would more readily be optimized by calculation than by further experiments. An analysis was made of the dynamics of the gimbal mounting and a computer model developed by means of which the value of viscous damping could be optimized for a spring stiffness by searching for the minimum value of an output function integrated over a range of components of an input power spectrum. Power spectra for roll and yaw were calculated from data recorded at three speeds over the standard bumpy test track. The polar moment of inertia of the boom was determined by bifilar suspension. Optimum values of damping were computed for ranges of natural frequencies. The experimental gimbal mounting was rebuilt to facilitate tests at ranges of polar spring stiffness and polar damping coefficient. The conditions giving minima in the response obtained were found to agree well with the values predicted by the computer model.

Instantaneous Frequency Estimation Using Adaptive Linear Predictor Weights

A computationally efficient scheme for estimating the digital instantaneous frequencies of narrowband inputs is introduced. The frequency estimates are obtained by searching for minima of the inverse input power spectrum. This spectrum is estimated at each input sample from the weights of an adaptive linear predictor which uses the LMS (least mean square) algorithm to update its weights. The related minima are sought via an iterative search algorithm, referred to as the iterative frequency estimator. This algorithm is computationally more efficient than available methods, and also provides a higher resolution. Simulation results are included; these include tracking of random message sequences in FM signals, and the formant frequency estimation of speech.

Long-time quasilinear evolution of the free-electron laser instability for a relativistic electron beam propagating through a helical magnetic wiggler

The long-time quasilinear development of the free-electron laser instability is investigated for a tenuous electron beam propagating in the z direction through a helical wiggler field B0=−B̂ cos k0zêx−B̂ sin k0zêy. The analysis neglects longitudinal perturbations (δφ≂0) and is based on the nonlinear Vlasov–Maxwell equations for the class of beam distributions of the form fb(z,p,t) =n0δ(Px)δ(Py)G(z,pz,t), assuming ∂/∂x=0=∂/∂y. The long-time quasilinear evolution of the system is investigated within the context of a simple ‘‘water-bag’’ model in which the average distribution function G0( pz,t) =(2L)−1∫L−L dz G(z,pz,t) is assumed to have the rectangular form G0( pz,t) =[2Δ(t)]−1 for ‖pz−p0(t)‖ ≤Δ(t), and G0( pz,t) =0 for ‖pz−p0(t)‖ &amp;gt;Δ(t). Making use of the quasilinear kinetic equations, a coupled system of nonlinear equations is derived which describes the self-consistent evolution of the mean electron momentum p0(t), the momentum spread Δ(t), the amplifying wave spectrum ‖Hk(t)‖2, and the complex oscillation frequency ωk(t) +iγk(t). These coupled equations are solved numerically for a wide range of system parameters, assuming that the input power spectrum Pk(t=0) is flat and nonzero for a finite range of wavenumber k that overlaps with the region of k space where the initial growth rate satisfies γk(t=0) &amp;gt;0. To summarize the qualitative features of the quasilinear evolution, as the wave spectrum amplifies it is found that there is a concomitant decrease in the mean electron energy γ0(t)mc2=[m2c4+e2B̂2/k20 +p20(t)c2]1/2, an increase in the momentum spread Δ(t), and a downshift of the growth rate γk(t) to lower k values. After sufficient time has elapsed, the growth rate γk has downshifted sufficiently far in k space so that the region where γk &amp;gt;0 no longer overlaps the region where the initial power spectrum Pk(t=0) is nonzero. Therefore, the wave spectrum saturates, and γ0(t) and Δ(t) approach their asymptotic values.

Resonant heating - an interpretation of coronal loop data

It is shown that the resonant heating theory of Hollweg can be used to organize the coronal loop data of Golub et al. (1980). When combined with a reasonable form for the input power spectrum, the resonant heating theory is fully compatible with the loop data.

Distortion of model subsurface radar pulses in complex dielectrics

The propagation of subsurface radar pulses in complex dielectric media is studied numerically. The model waveform is a 10‐ns sinusoidal cycle, and the media properties are similar to those of moist ground or sea ice. When the real part of the dielectric permittivity is frequency independent and the imaginary part is dominated by the dc resistivity, amplitudes of the positive and negative half cycles unbalance, and the sinusoidal zero crossing is delayed from its normal position. In these cases, if reflector depth is known, the dielectric constant can be measured from the time delay of the leading edge of the signal, and the dc resistivity can be estimated from a comparison of the input and output pulse power spectra. When dielectric permittivity is frequency dependent through a simple relaxation process, waveform distortion depends on relaxation frequency. In addition, if reflector depth is known, the dielectric relaxation parameters εs and ε∞ may be estimated when the medium relaxation frequency lies above and below the major portion of the pulse bandwidth, respectively.

Spectrum of the CM produced by high-intensity, low-frequency noise bands in the chinchilla

High-intensity, low-frequency octave band noise in the free field has been reported to produce permanent threshold shift at 2 kHz in chinchillas [Burdick, Patterson, Mozo, and Camp, J. Acoust. Soc. Am. 64, 458 (1978)]. We have delivered 100- and 250-Hz low-pass noise to the chinchilla with intact pinna but open bulla and have measured the spectrum of the CM recorded with electrodes in turn I and turn II. SPL's were measured at the pinna. The output of the microphone was led to channel 1 of an A/D converter. The CM was led to channel 2. The inputs to the A/D's were adjusted to the same rms level to minimize digital noise. A computer program calculated FFT's and produced several calculations from them (see previous abstract). At SPL's below 100 dB, the output spectrum (CM) is similar to the input spectrum (microphone). Above 100 dB the output spectrum contains frequencies above the passband of the input spectrum. The coherence function indicates that the high-frequency output is not present in the input power spectrum. [Supported in part by DAMD17-78C-8067 and NSF 77-16907.]

Acoustic properties of the external auditory canal in chinchilla, guinea pig, cat, and man

The acoustic pressures produced by a band of noise were measured at the entrance to the auditory canal and near the tympanum. The stimuli was produced by a TDH-39 earphone activated by a noise band tailored to produce an approximately flat spectrum between 0.1 and about 4 kHz at the entrance to the ear canal. A computer program calculated the output power spectra, the signal/noise, the cross-power spectrum, the transfer function, the coherence function, and the phase between the input and output power spectra. The transfer function in each animal shows an upper frequency peak, the location of which varies with the apparent volume of the canal, being highest for the guinea pig and lowest for man. The magnitude of the resonance is largest for the cat and smallest for the guinea pig. [Supported in part by DAMD 17-78C-8067 and NSF-77-16907.]

Vibration induced masking noise

Very high acoustical gradients negate acoustical privacy in buildings which normally have acceptable transmission loss between units. This is particularly true of mountain condominium complexes which have entertainment areas in the same building. The vibro-mask system reduces the acoustic gradient by introducing masking noise into the quieter areas such as sleeping quarters. Acoustical transducers induce structural vibration which is in turn transmitted throughout the building with a reasonable degree of uniformity. Equalization of the input power spectrum is accomplished by electronic networks to obtain the desired masking sound spectrum.

6.4 - Optical processing of flight test data

An optical analog computer has been demonstrated which is capable of obtaining quantitative estimates of transfer functions of systems from finite records of input and response data and power spectra of the input and response. The input <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x(t)</tex> and response <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">z(t)</tex> are recorded as amplitude-transmission variations on a photographic plate. To compute the power spectrum of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x(t)</tex> , the Fourier transform <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">X(\omega)</tex> of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x(t)</tex> is formed by illuminating <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x(t)</tex> with light from a He-Ne laser and focusing the resulting diffraction pattern with a lens to form <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">X(\omega)</tex> . This diffraction pattern, when read out with a properly-shaped light-gathering probe connected to a photomultiplier, will yield an estimate of the power spectrum of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x(t)</tex> . In a similar manner, the power spectrum of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">z(t)</tex> is estimated. To estimate the transfer function <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H(\omega)</tex> , a hologram of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">X*(\omega)</tex> is made. From the hologram, a transparency is made whose amplitude transmission is proportional to <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/ X*(\omega)X(\omega)</tex> . When the hologram is illuminated by <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Z(\omega)</tex> , the resulting diffraction pattern will contain <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">X*(\omega)Z(\omega).X*(\omega)Z(\omega)</tex> is then imaged onto the transparency whose amplitude transmission is <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/X*(\omega)X(\omega)</tex> forming <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H(\omega) = X*(\omega)Z (\omega)/ X*(\omega)X(\omega)</tex> . Experimental results are presented which indicate that good estimates of power spectra and transfer functions can be obtained by this method.