Pulsation Signal Research Articles

On the possibility to measure volumes of small gas bubbles and the bubble producing gas flow rates acoustically

Using the pulsation properties of gas bubbles it is possible to measure acoustically volumes c.q. equivalent diameters of gas bubbles in the range of 1.8–2.1 mm, produced at low frequencies at capillary tubes in a silent environment. Hence it is possible to measure very low gas flow rates (from 4 up to 100 mm3/s). During formation of bubbles at capillary tubes phenomena of repeated coalescence can occur between a just released bubble and the following bubbles under formation. This occurrence depends on the speed of rise, the bubble volume and the formation frequency. There is experimental evidence that this swallowing-up gives cause to a swinging-up of the amplitude of the pulsation signal. This coalescence process is the main physical limitation of the claimed method to low frequencies. There is also some experimental evidence by laser pulse synchronization between acoustics and bubble photographs that the often reported neck during bubble formation actually is an effect caused by this swallowing-up process.

Equivalent circuit of a magnetic sensor coil and a simple filter for rejection of 60Hz man-made noise.

A magnetic sensor coil is shown to behave as a 2nd order Butterworth low pass filter for induced e. m. f. if the coil's output ends are terminated with a set of parallel resistor and capacitor matched to the sensor. The conditions for matching are theoretically derived, assuming an equivalent circuit of the sensor coil. An experiment to check the Butterworth filter behavior agrees well with the theory. It demonstrates the validity of the assumed equivalent circuit of the sensor. The corner frequency of the filter can be changed, selecting different matched values of the resistor and capacitor. In the experiment, the corner frequency is set at 6Hz which rejects 60Hz man-made noise 40 db ca. without distorting magnetic pulsation signals up to the highest frequency range (Pc 1). This technique for rejection of man-made noise is more advantageous than another common practice, putting a twin-T filter between the sensor and the head amplifier. A twin-T filter used this way is shown to give rise to ringing depending on the characteristics of the sensor, the twin-T filter and the input impedance of the head amplifier.

The horizontal propagation of Pc1 pulsations in the ionosphere

The propagation properties of the various elements of the plane-wave angular spectrum of a Pc1 pulsation signal in the ionosphere are determined by a full-wave numerical analysis. A spectral component is characterized by the wave-vector azimuthal direction, and the Snell constant S. The isotropic R-mode transmission coefficient to ground is fairly flat for S ⩽ 400, but thereafter ( S > 500) drops rapidly with increasing S. Coupling of energy from the field-guided L-mode to the R-mode occurs along the entire length of the L-mode trajectory within the ionospheric duct in which the R-mode can propagate. Within the duct, the R-mode attenuation is determined largely by R to L-mode coupling, which is larger for E-W than for N-S azimuths, especially for steep angles of incidence ( S < 100). This should lead to enhanced injection of energy into E-W high altitude, high velocity paths, but to higher E-W attenuation at oblique angles. For oblique propagation ( S ⩾ 200) horizontal group velocities are slightly higher than the Alfvén phase velocity at the F-layer peak, but about twice as high for steep angles ( S ≈ 100).

Geomagnetic pulsation signals and hourly distributions of IMF orientation

Hourly distributions of the angle θXB=arccos (X · B), where X is the solar ecliptic earth‐sun axis and B is the interplanetary magnetic field (IMF), have been compared with hourly Pc 3 and Pc 4 signal activity at Calgary for 198 hours in September, October, and November 1969. Hours whose distributions were concentrated above or below θXB = 50° were correlated with a clear separation of inactive from active micropulsation intervals. The correlation was stronger for the Pc 3 than for the Pc 4 band, and hours with significant fractions, say 10–20% of their θXB distributions below 30°, corresponded particularly well with high amplitudes of micropulsation signals. Signals in the Pc 3 period range on the ground can therefore be used as a crude monitor of certain extremes of IMF orientation.

IMF orientation, solar wind velocity, and Pc 3‐4 signals: A joint distribution

Separate studies using the same micropulsation data base in the period range 10–150 s have shown earlier that signal levels recorded during September, October, and November 1969 at Calgary correlated positively with both solar wind alignment of the IMF and solar wind speed, but each correlation contained enough scatter to allow for influence of the other factor. In this report, joint correlations of velocity and field direction with parameters representing hourly distributions rather than minima of IMF orientation angle display the relative effect of the two agents on magnetic pulsation signal levels. The joint correlations reduce the overall scatter and show that solar wind speeds above 200–300 km/s and angles between the IMF and the sun‐earth line of less than 50°–60° are associated with enlarged magnetic pulsation amplitudes. These threshold effects tend to support both the bow shock origin and the Kelvin‐Helmholtz amplification of daytime signal transients in the Pc 3, 4 period ranges.

Source induced vertical components in geomagnetic pulsation signals

We show how large vertical components may be induced in geomagnetic pulsation signals because of the localised nature of the source. The effect is greatest when the signal varies on a horizontal scale length which is shorter than the skin depth of the signal in the Earth. However, the horizontal scale length is also constrained to be equal or larger than the height of the ionospheric E-region (∼ 120 km) as signals varying on a shorter scale are severely attenuated. Such conditions are best met by high latitude pulsations and some recent high latitude observations are explained by our results. We find that the vertical component is best correlated with the horizontal component in the direction in which the signal varies most rapidly.

On the orientation of hydromagnetic waves in the magnetosphere

We review evidence gathered from theoretical considerations and from measurements on the ground and in space for a 90° rotation of the major axis of the polarization ellipse of geomagnetic pulsation signals between the geomagnetic equator and the ground. The evidence at present supports the existence of the rotation phenomenon, although more observational work is needed. The rotation arises from the nonconducting air on the ground surface and the highly conducting plasma in space.

Damping of geomagnetic pulsations by the ionosphere

A significant sink of geomagnetic pulsation energy is due to Joule dissipation in the ionosphere. To investigate this we have computed the damping experienced by standing Alfvén waves in a dipole magnetic field. Both the uncoupled poloidal and toroidal modes are considered with Joule dissipation being introduced through a boundary condition which relates the electric and magnetic field strengths at the ionosphere, viz: 4πΣ p E c = b, where Σ p is the height integrated Pederson conductivity. The damping rates are strongly dependent on the ionospheric conductivity and we find that typically the normalized damping rate, γ ω , is ∼0.1 for nightside values of conductivity and ∼0.01 for the dayside. This would account for the observed scale of bandwidths in pulsation signals. Away from regions of extreme damping we find γ ∝ L −1 Σ p −1.

Suppression in pulsation-threshold patterns

In a pulsation, threshold experiment the frequencies and intensities of the two tones in the “masker” were fixed and the frequency of the signal was varied. The plot of pulsation threshold versus signal frequency is called the pulsation-threshold pattern of the “masker”. First the pulsation-threshold pattern was measured when the “masker” contained only a 1000-Hz tone. Then the patterns were measured for a 400-Hz tone and for a 1500-Hz tone. Finally, the pattern was measured when the masker contained both the 1000-Hz tone and either the 400-Hz tone or the 1500-Hz tone. The 400-Hz tone was able to reduce the pulsation thresholds around 1000-Hz by 20 dB or more for each of the three subjects. The 1500-Hz tone did not reduce the pulsation thresholds at 1000 Hz but did at 1100 Hz, i.e., on the high-frequency tail of the 1000-Hz pattern. Suppression is assumed to be the cause of these reductions. Thus one tone is able to suppress only part of the excitation pattern of another tone. Mutual suppression was also indicated for one subject. Relationships to partial masking will be discussed. [Work supported the NINCDS.]

Frequency-time analysis of geomagnetic beating-type pulsationsPc3

The mechanism of beating of Pc3 type pulsations is studied. Using the method of numerical computation of a sonagram (the method of frequency-time analysis) a set of samples of pulsations from the Budkov Observatory is treated (1968–1969) mostly at K-indices equal to 2–3. By comparing f–t diagrams with the spectra of the samples an attempt has been made at interpreting the beating as a superposition of the frequency components, contained in the pulsation signal. In most observed cases it is possible to determine two close frequencies, the difference of which is on the average\(\overline {\Delta f} \)=5.4 mHz. The average carrier frequency of the samples was\(\bar f_0 \)=37.6 mHz, and the average frequency of the beating\(\bar f_B \)=2.7 mHz. The interval of observed values of fB amounted to 1–5 mHz. A tendency was observed for fB to increase with increasing degree of disturbance of the geomagnetic field.

Thin-Probe Pulsed-Light Photometer for Measurement and Calibration of Timing and other Pulsed-Light Sources

The apertures of timing blocks, by which range-timing signals are “written” on the film record, are inaccessible for normal photometry. Measurements of this type are made with a new thin-probe pulsed photometer sensitive to 0.01 fL and versatile to use. The photometer's circuitry is sensitive only to pulsating light signals; it will not respond to the continuous ambient light levels normally encountered in the field or laboratory. With expanded ranges and scales of light sensing and higher bandpass characteristics, the instrument predicts the film exposure at all film speeds and frame rates. Additional plug-in probes adapt the meter-amplifier for a variety of measurements in numerous fields where a small, sensitive pickup is required.

The pulse stretch coupling circuit

This paper describes a new coupling circuit applicable to both half-wave and full-wave magnetic amplifiers, particularly those amplifiers simultaneously requiring fast time response and large power gains. The pulse stretch technique uses a pulsating bias signal derived from an external supply to block the power winding of the reactor during reset. This blocking action permits free core control yielding an amplifier with an improved figure of merit.