Quasi-periodic Components Research Articles

Transformation and decomposition of the speech signal for coding

The speech signal is represented by an evolving characteristic waveform. The characteristic waveform is decomposed into a slowly evolving waveform and a rapidly evolving waveform, representing the quasi-periodic and other components of speech, respectively. These two evolving waveforms have fundamentally different quantization requirements. The decomposition allows efficient coding of voiced and unvoiced speech at bit rates between 2 and 8 kb/s.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Quasiperiodic and chaotic self-excited voltage oscillations inTlInTe2

The electrical behavior of the ${\mathrm{TlInTe}}_{2}$ ternary semiconductor is studied in the negative-differential-resistance region of its S-type I-V characteristic. Self-excited voltage oscillations in this region, with an amplitude of about 5 V were monitored at temperatures above 70 K. An analysis of the dynamic behavior of these oscillations by means of the Grassberger and Proccacia method shows the existence of two components in the signal, a quasiperiodic component and a chaotic component. Furthermore, this analysis leads to the estimation of fractal dimensions, minimum embedding dimensions and Kolmogorov entropies that characterize the two components.

Ultrasound speckle reduction using harmonic oscillator models

A speckle reduction algorithm called the harmonic imaging (HI) algorithm is presented. It is based on a multicomponent scattering model for medical ultrasonics. The backscattered ultrasound quadrature signal is modeled as the sum of three components after demodulation. The first component represents nonresolvable diffuse scatterers, while the second component represents subresolvable quasi-periodic scatterers. The third component represents resolvable quasi-periodic scatterers and mirroring surfaces. Since the second component gives rise to the most long range destructive interference effects it is eliminated in the HI algorithm to reduce speckle. Due to its slow spatial variation, it can be almost completely eliminated simply by differentiating the backscattered demodulated quadrature signal. Lissajous-like figures are observed in complex plots of the signals from ultrasound beams going through tissues with quasi-periodic components and sometimes in areas with only diffuse scatterers. Therefore the sum of the complex signals from the resolvable and nonresolvable scatterers within a resolution cell is modeled by two orthogonal and independent harmonic oscillators. The estimated, total energy of these two oscillators determines the gray level value of the HI image within the resolution cell. The HI images produced using radio frequency data from a phantom and from tissues in vivo are more blurred than ordinary envelope images, but the signal to noise ratio and tissue contrast were higher for the HI images.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Dynamics of fluid mixing in separated flows

The dynamics of the flow in the separated region and near wake of a vertical flat plate was analyzed with the phase-locked laser-Doppler technique at Reynolds number Re=2.8×104. The flow exhibits an intense quasiperiodic component at a Strouhal frequency of St=0.14. The vortex shedding process was resolved into six phases, resulting in a time difference between consecutive phases of Δt=0.02 sec. Interactions between the free shear layers, emanating from the model edges, lead to nonlinear dynamics of the flow. The distributions of the Reynolds stresses indicate that maximal amplitudes in the normal stresses 〈u′2〉 and 〈v′2〉 as well as in the shear stress term 〈u′v′〉 are provoked by positive pressure gradients in the shear layer flows upstream of saddle points. Saddles are quasiperiodically formed by interactions between the two free shear layers. Regions with enhanced Reynolds stresses and saddles are convectively transported within the flow field.

Barometric tides in partly-saturated confined aquifers in Botswana

Barometric fluctuations in Botswana are dominated by atmospheric tides with frequency components of 6, 8, 12, and 24 h, as well as quasi-periodic components with a periodicity of 4–7 days. These tides cause periodic water level fluctuations in the majority of the boreholes in fracture aquifers. Many of these aquifers are partly saturated and show free water table characteristics, but are separated from direct atmospheric influence by less-pervious beds near the surface. The barometric effect is caused by an imbalance between the water pressure change in the well and in the aquifer. A theoretical model is presented that includes the compression of the aquifer and the associated vertical flow through the aquifer to the water table. The model qualitatively explains the observed frequency-dependent phase and amplitude response. The generally observed strong barometric effects are explained by a combination of high porosity and low conductivity.

The Al-Mn decagonal phase Part 3. Diffraction pattern simulation based on a new index scheme

Abstract Abstract A proposal to abandon the current sophisticated index scheme of the Al-Mn decagonal phase has recently been advanced (Fitz Gerald, Withers, Stewart and Calka 1987), in favour of a new straightforward description. This description is based on a periodic stacking of Penrose lattices which are two-dimensional, using the natural in-plane (quasi-periodic) a 6 (n = 1 to 5) and (periodic) a 6 vectors as its basis. It affords a simpler description than the currently adopted system which is based on the lower and upper edge vectors of a (distorted icosahedral) pentagonal bipyramid model, with useful advantages for example in comparing vectors of identical quasiperiodic but different periodic components. Computing the diffraction pattern is straightforward in our description, and our simulations show excellent agreement with patterns recorded experimentally at various projection angles.

Low-frequency variation in the seasonal intensity of coastal weather systems and sediment movement on the beachface of a sandy beach

Variation in the seasonal intensity of weather systems generating onshore winds incident on Port Kembla, N.S.W., have been examined for the period 1965 to 1983. The onshore-wind events were identified from anemograph records. In turn, they were related to synoptic weather records. An intensity index (1) for each weather system was estimated as a function of the barometric pressure gradient between Port Kembla and the system centre. The events were grouped by seasons and the intensity of the upper-tercile ( I 1 3 ) value for each season, utilised to represent the record for that season. Values of the seasonal I 1 3 intensities were spectrally analysed by Fast Fourier Transform techniques. The results identified quasi-periodic variations of onshore wind activity with recurrence intervals corresponding to those in the frequency band shared by the Southern Oscillation (SO), as well as the stratospheric Quasi-Biennial Oscillation (QBO) and the tropospheric quasi-biennial oscillation (BO). The dominant quasi-periodic components, identified from a time series filtered to remove high frequency fluctuations, include 3 years, 27 months and 21.6 months. The triennial and biennial components combine to account for approximately 32% of variance in the time series describing seasonal I 1 3 anomalies in onshore wind activity. The filtered time series correlated with the Southern Oscillation Index (SOI) ∗ ∗ Angell (1981). , with r = 0.49, p < 0.0001. The co-spectra for 14 years of the two series were examined for coherence and found to be 99% significant for each, at 2.2 and 3.5 years. The phase relationship between the two time series indicated that the SOI led the onshore-wind intensity by approximately one season. (This is the limit of accuracy afforded by the wind data.) A good correspondence of the I 1 3 anomalies with the period of both the QBO and the M1 index of the tropospheric biennial oscillation were also noted. In the latter instance, direct comparison of the M1 phase shift ∗∗ ∗∗ Trenberth (1980). was not possible because the I 1 3 data is contaminated with a strong SOI type signal. Peak I 1 3 - intensities are in phase to ±1 month with the monthly mean-sea-level peaks at Fort Denison, Sydney, N.S.W., over corresponding periods. More accurate resolution is not possible because of the specification of the weather system intensities as seasonal values. In turn, the sea-level fluctuations lead movement of sediment on Warilla Beach, N.S.W., by a month. Over the 9 years for which observations are available from 1976 to 1985, peak weather-system intensities for Port Kembla are co-incidental with low volumes of sediment stored above MSL on Warilla Beach. Conversely, periods of low onshore-wind activity are associated with increases in the volume of sediment stored on the beach.

Novel motion in highly excited two-electron atoms

Exact rigid-body solutions for two-electron atoms have been derived within classical mechanics. These solutions describe equilibrium configurations of the electrons, i.e., the electrons do not experience any force. Exactly two nondegenerate equilibria exist with singly periodic rotation. Linear stability of these classical solutions emerges from the structure of highly nonlinear, coupled equations of motion rather than from geometrical potential barriers. This new type of strong correlation effect generates an atomic rotation spectrum of resonances converging to the double-escape threshold. These resonances should be observable in multiphoton absorption spectra. The binding mechanism of these resonances is provided by trapping the correlated electron pair onto an attractive phase-space domain. The motion within this basin of attraction consists of periodic, quasi-periodic, and chaotic components.

Measurement of a quasiperiodic component in a vibratory-acoustic signal from rotor mechanisms without a synchronizing signal

Measurement of a quasiperiodic component in a vibratory-acoustic signal from rotor mechanisms without a synchronizing signal

Charge-density-wave transport in quasi-one-dimensional conductors. I. Current oscillations.

We present a detailed experimental study of current oscillation phenomena in charge-density-wave (CDW) transport. The amplitude and harmonic content of the quasiperiodic component of the current oscillations remain large and approximately constant even at very high electric fields, suggesting that the form and magnitude of the impurity pinning potential are approximately independent of applied field. A simple single-coordinate model of CDW motion in a nonsinusoidal pinning potential, motivated by the quantum tunneling theory of CDW depinning, accounts for all the qualitative features of our results. Nearly perfect velocity coherence seems to be characteristic of weak-impurity-pinned CDW's in high-quality ${\mathrm{NbSe}}_{3}$. However, other types of crystal defects together with contact effects act to broaden the observed distribution of CDW velocities. This velocity distribution plays a crucial role in the ``ringing'' observed in the CDW response to a current pulse, and also in generating the broadband noise.

On quasiperiodic microvariability of V 351 Ori

Spectral analysis of long series of observations of the variable star V 351 Ori has revealed a quasiperiodic component in the variations of the light with a period of P = 326 + or - 4 sec. The amplitude of the quasiperiodic variations of the light in the ultraviolet region of the spectrum is greater than in the blue part and varies from 0 /sup m/ .06(U) (at the normal brightness of the variable) to 0 /sup m/ .15(U) (when the brightness has faded by 1 /sup m/ .6(V)).

On the origin of quasi-periodic current noise in charge-density wave conductors: Experiments on orthorhombic tantalum trisulphide

The quasi-periodic components, which appear in the voltage V developed across a charge-density wave (CDW) conductor when the steady current I exceeds the threshold current I T at which motion of the CDW begins, have been observed in orthorhombic TaS 3 at 77 K at frequencies v down to less than 1 Hz. Although its relation to the nonlinear part of the current when I⋙ I T indicates that v is, or is a low multiple of, the ‘washboard’ frequency v/λ, where v is the velocity and λ the wavelength of the CDW, the amplitude of the periodic variation of V when v<1 kHz is much too great to represent a modulation of the Frohlich current. The alternative is that the variation of V arises from a periodic modulation of the single-electron conductivity, resulting from distortion of the CDW as it moves through the crystal. Such a modulation of conductivity has been demonstrated experimentally, by interrupting a current I> I T at different stages of the cyclic variation of V, and then using a current I< I T to observe the resistance of the specimen when the CDW is at rest. Mechanisms whereby a periodic dependence of resistance on the position of the CDW may arise are briefly discussed.

Spectral Analysis of Yarn irregularity and Its Relationship to Other Yarn Characteristics

Spectral analysis was used to break up the yarn irregularity into periodic, quasiperiodic, and random components for three different counts, namely 20 tex (30s Ne), 9.9 tex (60s Ne), 5.9 tex (100s Ne), spun at three different levels of drafts and four levels of top and bottom roller eccentricities, and their combinations. The periodic component increases nonlinearly at higher eccentricities and higher drafts and there is also an increase in quasiperiods. This behavior contradicts the commonly accepted theory of linear increase put forward by Foster. The thin and thick places in yarn increase nonlinearly, whereas single thread strength drops rapidly at higher levels of eccentricity and draft. Yam appearance grades deteriorate, particularly with increase in the periodic component. At comparable levels of irregularity, periodic component leads to a diamond barring effect, whereas existence of higher quasiperiods dampens the diamond bars by confounding the periodic component.

The existence of quasi-periodic oscillations with periods from a minute up to some hours in the solar radio emission at ? = 3 cm

Quasi-periodic components (QPC) of the solar radio emission may give information about the wave (oscillation) motions in the whole depth of the solar atmosphere. Investigations of quasi-periodic components (QPC) of the radio emission fluctuations give contradictory and often doubtful results. Special care must be taken when registering fluctuations and peculiar attention have to be paid to the correctness of the mathematical processing. Results of investigation are given of the solar radio emission fluctuations carried out by 3 cm radio telescopes 1300 km spaced. The reality of QPC existence with the periods from a minute up to some hours is shown. QPC with the periods 1–10 min change during 2 hours. Some possibilities of the origin of oscillations observed are considered.

High resolution interferometry of the Sun at 3.7 cm wavelength

Interferometric observations of the Sun at a wavelength λ = 3.7 cm and an effective angular resolution of θ = 7 or 15″ are presented. When active regions are observed, circularly polarized radiation is found with an angular size of θ ≈ 15″, an effective temperature of T ≈ 5 × 105K, and 20 to 30% circular polarization. This S-component of solar radio radiation is interpreted in terms of the theory of gyroradiation and gyroresonant absorption. Prior to the onset of a solar flare, an additional S-component is observed with an angular size of θ ≲ 7″, an effective temperature of T ≥ 106 K, and 90 ± 10% circular polarization. A small scale, quasi-periodic component of solar radio radiation is also observed to be coming from all over the solar disk; and this component is found to be less than 10% circularly polarized. The angular sizes, θ, and periods, P, of this component lie in the ranges 7″ ≲ θ % 37″ and 180 s ⪞ P ≲ 750 s. The observed modulation in flux density, ΔS, lies in the range 20 f.u. ≲ ΔS ≲ 200 f.u. (1 f.u. = 10-26 Wm-2 Hz-1 or 10-23 e Hz-1) and the brightness temperature fluctuations, ΔT, lie in the range 103K ≲ ΔT ≲ 105K. This component of solar radio radiation is thought to be the free-free radiation (bremsstrahlung) of temperature fluctuations associated with velocity oscillations in the chromosphere-corona transition region. High resolution observations of impulsive microwave bursts show that some of the radiation is linearly or circularly polarized, has an angular size θ ≤ 7″, and a peak brightness temperature of T ≳ 3 × 106K. This component of solar radio flares is interpreted in terms of the theory of gyro-synchrotron radiation, and the density of accelerated electrons is found to be greater than 100 cm-3. The size of the emitting region is, however, comparable to that of the feet of magnetic dipoles rather than the region between them. Phase shifts in the interferometer pattern observed during an impulsive burst are interpreted in terms of hydrodynamic waves travelling at a velocity of 7000 km s-1, but further observations are needed to confirm the result.

Quasiperiodic components with periods of from 30 to 60 min in the fluctuation spectra of solar radio emission at the 3 cm wavelength

Quasiperiodic components with periods of from 30 to 60 min in the fluctuation spectra of solar radio emission at the 3 cm wavelength

Quasiperiodic Components in the Fluctuations of the Solar Radio-frequency Radiation

Quasiperiodic Components in the Fluctuations of the Solar Radio-frequency Radiation

О квазипериодических компонентах во флуктуациях солнечного радиоизлучения

О квазипериодических компонентах во флуктуациях солнечного радиоизлучения

On quasi-periodic components with periods from 30 to 60 min of amplitude fluctuations of X-band solar radio emission

Special experiments have been performed to investigate the fluctuations of the intensity difference of the solar radio emission at two close frequencies. The autocorrelation functions and their spectra are obtained. The latter shows the presence of quasi-periodical components with periods of about 50 min in the solar radio emission. The possibility of explaining the observed quasi-periodical components by the supergranulation oscillations and the solar self-oscillations is considered.

Periodicity of 3C 273

THE possible periodicity of QSO 3C 273 has been widely discussed1–12. The Lebedev group1–6 has maintained that evidence exists for a nine-year quasiperiodic component of the luminosity whereas the other authors (with the exception of Smith11) have generally held a sceptical point of view. Here I make no independent claims one way or the other; in reviewing the conflicting statements, however, it became apparent that few investigators had a clear idea of the basis for the claims of the Lebedev group. The purpose of this communication is to report the results of an application of the method of the Lebedev group to various versions of the 3C 273 data and to shot noise data. A critical discussion is presented of the claims for periodicity based on this method.