Sinusoidal Period Research Articles

A new technique for adaptive frequency estimation and tracking

A new technique is presented for estimating the frequency of a sinusoid in noise. Standard techniques typically estimate the frequency of a sinusoid from an estimate of the autocorrelation function or from a filter model. These techniques require a large number of samples for an accurate estimate of the frequency. Furthermore, if the frequency is varying with time, recomputation of the autocorrelation or filter model is necessary for each estimate update. In this correspondence, we present a new technique that is based on a variable delay element. We will show that the corresponding error surface is sinusoidal, and that the first maximum of the error function occurs at one-half the period of the unknown sinusoid. We will develop an algorithm that is based on gradient techniques to find this maximum, and from this maximum we directly compute the frequency estimate. The new algorithm works in the time domain with a simple adaptive delay update computation. The technique has been tested in simulations with signal-to-noise ratios as low as 1 : 10, with excellent performance. The speed of the algorithm depends on a convergence factor that is computed from an initial estimate of the power of the input signal. Since the technique is adaptive, it can also be applied to tracking a time-varying frequency.

Ventilatory and gas exchange responses to cycling with sinusoidally varying pedal rate.

To investigate factors controlling ventilation under conditions where the applied work load remains constant, but where hypothesized proprioceptive influences would be expected to vary, five subjects exercised at a constant work rate of 50 W on a cycle ergometer at pedaling rates which varied sinusoidally between 40 and 80 rpm. Each subject exercised continuously for 30 min at each of five sinusoidal periods. Minute ventilation (VE), carbon dioxide output (VCO2), oxygen uptake (VO2), and heart rate were computed breath-by-breath and amplitude and phase relations were extracted. We observed small fluctuations in VCO2 and VO2 engendered by varying metabolic requirements of moving the legs at varying rates. VE fluctuations were closely in phase with VCO2 and the amplitudes of the fluctuations were highly significantly correlated (r = 0.83, P less than 0.001); consequently end-tidal carbon dioxide tension fluctuations were small. Variation of pedaling rate, therefore, did not produce a ventilatory response independent of the effect of VCO2. The ventilatory responses to these forcings are inconsistent with an appreciable role for neurally mediated influences from the exercising limbs and provide further evidence that the exercise hyperpnea is linked to CO2 flow to the central circulation.

AK Herculis ? An atypical W UMa-type system

AK Herculis is a contact binary of spectral class F with a number of obvious peculiarities such as a displacement of secondary eclipse from phase 0 . P 500, unequal heights of the maxima, and a possibly sinusoidal (≃60 yr) period variation. The light curve is variable and shows erratic short-term behavior, although the latter effects are not unusual for a short period contact binary. Here we present new photoelectric light curves in theB andV passbands and derive several new times of minima. The new observations are compared graphically with seven earlier light curves. We analyzed the new observations and those by Bookmyer (1972) by the method of differential corrections. We find that the temperature difference between components is too large (≃1000 K) for AK Her to be considered a normal W UMa-system, but too small to allow a detached configuration obeying the mass-luminosity law. The solutions of both series of observations clearly indicate a contact configuration. Other unusual findings include a bolometric albedo greater than 2, and rather low values for the limb-darkening coefficients. We offer some possible reasons for these peculiarities. The mass ratio seems well determined from the photometry and is about 0.26, which is much lower than assumed in most earlier papers. The brightness and color of the known visual companion, ADS 10408B, were found by the differential corrections program. They agree, within observational error, with values found directly at the 200-in. telescope by Eggen, despite the fact that the B component contributes only a few percent of the light of the multiple system. The suggestion by Schmidt and Herczeg (1959) that a fourth body is responsible for the sinusoidal period variation seems stronger now than when first proposed. To encourage a search for this hypothetical component, we have tabulated expected values for its angular separation and relative mass with respect to the eclipsing pair, as well as the amplitude of the expected variable proper motion of the eclipsing pair. Discovery as a visual component seems impossible with present means, but the variable proper motion should be detectable. Thus we suggest that ADS 10408A (AK Her) be observed astrometrically. If a search for the predicted variable proper motion proves negative, mass transfer would remain the only plausible mechanism to explain the period change. We advance a different reason than did Schmidt and Herczeg to explain the phase lag of secondary eclipse.

Ventilatory and gas exchange dynamics in response to sinusoidal work.

The dynamic relationships between ventilation and gas exchange variables during exercise were determined utilizing frequency analysis techniques. Five subjects exercised on a cycle ergometer for 30 min at work rates which fluctuated sinusoidally between 25 W and 80% of the anaerobic threshold at sinusoidal periods of 0.7, 1,2,4,6, and 10 min. VE, VCO2, VO2, and HR were computed and displayed breath-by-breath. From these and steady-state response data, digital computer routines extracted amplitude and phase relations between each variable and the perturbing work load. These response characteristics were well described by first-order linear dynamics with time constants for VE, VCO2, VO2, and HR averaging 1.4, 1.2, 0.8, and 0.8 min, respectively. The time constants of VE and VCO2 were strongly correlated among subjects (r = 0.97). Further, there was no evidence that neural afferents from the exercising limbs induced fast components in the ventilatory response to these forcings. These results are consistent with the hypothesis that exercise hyperpnea is linked to metabolism via carbon dioxide production.

Mass transfer in DQ Her.

New observations of the 279/sup m/ binary period and 71/sup s/ sinusoidal period are presented. From these and other data we derive an upper and lower bound and an estimate for the mass transfer rate. Luminosity of the system based on the value of the mass transfer rate is discussed. (AIP)

Analysis technique for classifying wind- and ship-generated noise characteristics

An analysis technique is described that permits the classification of ambient noise sources (wind generated and shipping) without the need for information concerning the environment or shipping in the area of interest. Wind-generated and ship-generated ambient noise, or a combination of the two, can be classified by finding the zero-axis crossing time of the autocorrelation function versus frequency of the long-term (greater than two weeks) ambient noise time series for a given geographic area. Results obtained from the zero-axis crossing times of the autocorrelation function of ambient noise level versus time (measured by omnidirectional hydrophones and processed through 1/3-octave filters) are bounded by two distinct zero-axis crossing times. Analysis of data from four widely separated geographic areas produces the same bounds, which suggests that they may be independent of area. In the region of the spectra where 1/3-octave bands were highly correlated with wind speed, the decorrelation time (i.e., zero-axis crossing) was found to range from 26 to 40 h. In the region of the spectra that was not wind correlated and, therefore, attributed to ship-traffic noise, the decorrelation time was found to range from 4 to 8 h. For spectra that were composites of both noise sources, the decorrelation time ranged between 8 and 26 h. The observed correlation functions were fitted to a two-term equation to aid in determining the decorrelation times for all values of the wind-generated to ship-generated noise-level ratios. Each term of the equation (one being wind related and the other ship related) is a sinusoid whose decay parameter is equal to its corresponding mean value decorrelation time and whose sinusoidal period is four times that value. Subject Classification: 30.70, 30.80.

HEAT-TRANSFER IN A TAYLOR VORTEX FLOW

The characteristics of heat transfer affected by Taylor vortex motion were investigated experimentally by the use of electrochemical method and theoretically with the aid of the nonlinear theory suggested by J. T. Stuart. The present non-linear theory, which considers the effect of the fundamentals of disturbances on heat transfer, especially in the wide gap problem, is also applicable to the heat-transfer problem in the range of 1<Re/Recr<2 for fluid with Pr=1. The local Nusselt numbers (Sherwood numbers) measured by means of electrochemical technique show a remarkable sinusoidal periodicity in the axial direction due to Taylor vortex motion, except for their cycloidal periodicity in a very short supercritical range of Reynolds number. The values of skin friction and heat-transfer coefficient calculated by the semiempirical modification of the equilibrium amplitude of supercritical disturbances agree quite well with measurements over an unexpectedly wide range of Reynolds number (2<Re/Recr<20) where higher-order disturbances should be taken into account.

Electromagnetic wave propagation and wave-vector diagram in space-time periodic media

The electromagnetic wave propagation and wave-vector diagram in generally space-time periodic dielectric, plasma, and uniaxial plasma are studied for TE and TM waves. The case of a sinusoidal periodicity is solved numerically. Special properties due to the inhomogeneity are presented.